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ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 1
ELS: 2.4.1 POWER ELECTRONICS
Introduction
 Electrical power is the rate at which electrical energy is transferred by an electric circuit.
W
P =
t
where:
 P is the power,
 W is the work done or energy transferred,
 t is the time over which the work is done or energy is transferred.
 It quantifies the amount of energy consumed or produced by electrical devices and systems
over time.
 The fundamental definition of electrical power (P) is given by the product of voltage (V)
and current (I)
P = V×I
where:
 P is the electrical power measured in watts (W),
 V is the voltage measured in volts (V),
 I is the current measured in amperes (A).
 The SI unit of electrical power is the watt (W), defined as one joule per second (J/s).
 Electrical power can be expressed in several forms depending on the variables involved.
 By substituting Ohm's Law into the basic power equation P = V×I, we get the other
forms:
 Substituting V=I⋅R into P=V⋅I: 2
P = I×R ×
) I = I
( ×R
 Substituting
V
I
R
 into IP=V⋅I:
2
R
V
( )
R
V
P = V× =
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 2
Power Electronics
 Definition: Power Electronics is a specialized branch of electronics that deals with the
study and application of electronic devices and circuits for the efficient control,
conversion, and management of electrical power.
 This field encompasses the design, implementation, and application of devices and
systems for efficient power conversion and management.
 The field of power electronics can be well understood by dividing it into two subcategories;
i. Power Engineering: The field of power engineering mainly deals with the
generation, transmission, distribution, and utilization of electrical energy at higher
efficiency.
ii. Power Electronics Engineering: Basically, in power electronics, solid-state
electronics, is used that performs the action of control and convert of the electric
power.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 3
Comparison Between Electronics and Power Electronics
Aspect Electronics Power Electronics
Purpose Processing, transmitting,
and storing information
Conversion, control, and conditioning of
electric power
Voltage and
Current Levels
Typically low (mV to a few
V, mA to a few A)
Typically high (kV, A to kA)
Power Handling Typically milliwatts to watts Watts to megawatts
Primary
Components
Resistors, capacitors,
inductors, diodes, transistors
Power Diodes, Power Transister,
thyristors(SCR), MOSFETs, IGBTs,
transformers
Applications Computers, communication
devices, consumer
electronics
Power supplies, motor drives, renewable
energy systems
Switching Speed Generally high Moderate to high, but with higher power
handling
Heat Dissipation Heat dissipation is relatively
low.
Heat dissipation is a significant concern
due to high power levels, requiring
efficient cooling systems.
Thermal
Management
Less critical, often passive
cooling
Crucial, requires heat sinks, cooling fans,
or liquid cooling
Efficiency Less focus on efficiency High efficiency is critical
Design Focus Signal integrity,
miniaturization, low power
consumption
Efficiency, thermal management, high
power handling
Frequency Range High frequency (kHz to
GHz)
Low to moderate frequency (Hz to kHz,
sometimes MHz)
Control
Characteristics
Logic levels, signal
processing
Switching losses, conduction losses,
thermal stability
Protection
Requirements
Basic (overvoltage,
overcurrent)
Advanced (overvoltage, overcurrent,
thermal shutdown)
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 4
Need of Power Electronics
Power electronics is crucial for modern technology and industry due to its ability to efficiently
convert, control, and manage electrical power. Here are the key reasons for the need for power
electronics:
1. Energy Efficiency
Power electronics helps in improving the efficiency of energy conversion and utilization. By
minimizing energy losses during conversion processes, it contributes to significant energy
savings and reduced operational costs.
2. Renewable Energy Integration
With the increasing adoption of renewable energy sources like solar and wind power, power
electronics plays a vital role in converting and managing the variable output of these sources to
ensure a stable and reliable power supply.
3. Electric Vehicles (EVs)
Power electronics is essential in electric vehicles for efficient battery management, motor
control, and power conversion. It enables the development of EVs with longer ranges, faster
charging times, and improved performance.
4. Industrial Automation
In industrial settings, power electronics is used for precise control of machinery and processes.
Variable frequency drives (VFDs) and other power electronic devices allow for the efficient
control of motors, leading to improved productivity and energy savings.
5. Consumer Electronics
Power electronics is integral to the operation of various consumer devices, from smartphones
and laptops to household appliances. It ensures these devices operate efficiently and reliably by
managing power supply and distribution.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 5
6. Power Quality and Reliability
Power electronics improves the quality and reliability of power supplied to both industrial and
consumer applications. It helps in mitigating issues like voltage sags, harmonics, and power
interruptions, ensuring a consistent and stable power supply.
7. Miniaturization and Compact Design
The advancements in power electronic components allow for the development of smaller,
lighter, and more efficient power systems. This miniaturization is essential for portable
electronic devices and modern electrical equipment.
8. Smart Grids and Energy Management
Power electronics is a key technology in the development of smart grids, which use advanced
communication and control techniques to optimize the distribution and consumption of
electricity. It enables better energy management, load balancing, and integration of distributed
energy resources.
9. Cost Reduction
By improving efficiency and reducing energy losses, power electronics can lead to significant
cost savings in energy generation, transmission, and consumption. This is particularly important
in large-scale industrial applications and utility grids.
10. Environmental Impact
Efficient power conversion and management reduce the overall energy consumption and carbon
footprint. Power electronics supports the transition to cleaner energy sources and promotes
sustainable energy practices.
Therefore, the need for power electronics arises from its ability to enhance energy efficiency,
integrate renewable energy, support the development of electric vehicles, improve industrial
automation, ensure reliable power supply, and contribute to environmental sustainability.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 6
Importance of Power Electronics:
 Efficiency: Power electronics enables highly efficient energy conversion, reducing energy
losses.
 Control: Provides precise control over the delivery and quality of power.
 Miniaturization: Allows the development of compact and lightweight power systems.
 Integration: Facilitates the integration of renewable energy sources into the power grid.
Power electronics is a critical field that supports the development of advanced technologies and
sustainable energy solutions, playing a vital role in modern electrical and electronic systems.
Applications of Power Electronics
Power electronics is a versatile technology that finds applications across a wide range of fields.
Here are some key applications in various sectors:
1. Renewable Energy Systems
 Solar Power: Converters and inverters are used to convert the DC output of solar panels
into AC for grid integration or local use.
 Wind Power: Power electronics control the variable output of wind turbines and convert it
into a stable AC supply.
 Energy Storage: Battery management systems (BMS) and power converters manage the
charge and discharge cycles of energy storage systems.
2. Electric Vehicles (EVs)
 Motor Drives: Inverters control the electric motors, providing efficient and smooth
operation.
 Battery Chargers: Power electronic converters manage the charging process, ensuring
fast and safe charging of EV batteries.
 Regenerative Braking: Converts kinetic energy back into electrical energy to recharge the
battery during braking.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 7
3. Industrial Applications
 Motor Drives: Variable frequency drives (VFDs) and servo drives control industrial
motors, enhancing efficiency and precision.
 Welding: Power electronics control the welding process, providing consistent and high-
quality welds.
 Power Supplies: Switch-mode power supplies (SMPS) and uninterruptible power supplies
(UPS) provide reliable and efficient power to industrial equipment.
4. Consumer Electronics
 Power Adapters and Chargers: Convert AC to the appropriate DC voltage for devices
like smartphones, laptops, and tablets.
 Home Appliances: Efficient motor control and power management in appliances like
washing machines, refrigerators, and air conditioners.
 Lighting: LED drivers and dimmers control the brightness and efficiency of LED lighting
systems.
5. Power Grids and Utility Systems
 Smart Grids: Power electronics enable the integration of distributed energy resources,
enhance grid stability, and optimize energy distribution.
 HVDC Transmission: High-voltage direct current (HVDC) systems use power electronics
for efficient long-distance power transmission.
 FACTS Devices: Flexible AC Transmission Systems (FACTS) improve the reliability and
capacity of power transmission networks.
6. Transportation
 Rail Systems: Power converters and inverters control the traction motors of electric trains,
improving efficiency and performance.
 Aerospace: Power electronics manage the electrical systems of aircraft, ensuring reliable
and efficient operation of avionics and other onboard systems.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 8
7. Healthcare
 Medical Equipment: Power supplies and converters are crucial for imaging equipment
(MRI, CT scanners), diagnostic devices, and patient monitoring systems.
 Implantable Devices: Efficient power management in devices like pacemakers and insulin
pumps.
8. Telecommunications
 Power Supplies: Reliable power conversion and backup systems for telecommunication
equipment and data centers.
 Signal Processing: Power electronics are used in the amplifiers and transmitters of
communication systems.
9. Military and Defense
 Radar and Communication Systems: Power electronics ensure the efficient operation of
radar, communication, and other defense systems.
 Electric Propulsion: Used in naval and other defense vehicles for efficient propulsion and
power management.
10. Environmental Control Systems
 HVAC (Heating, Ventilation and Air Conditioning Systems) Systems: Variable speed
drives and inverters control heating, ventilation, and air conditioning systems for better
efficiency and comfort.
 Energy Management Systems: Power electronics are integral to systems that monitor and
optimize energy usage in buildings and industrial plants.
Power electronics is a critical technology enabling advancements in energy efficiency, renewable
energy integration, and the development of modern electronic and electrical systems across diverse
fields.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 9
Power Semiconductor Devices
 Power semiconductor devices have revolutionized the way we manage and control
electrical power.
 The journey began with early vacuum tubes and crystal detectors in the early 20th century.
 A significant milestone was achieved in 1947 with the invention of the transistor at Bell
Labs, accelerate the way for modern electronics.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 10
I. Vacuum Tubes
 Early 20th Century: Vacuum tubes, also known as thermionic valves, were the first active
electronic components used for amplification, switching, and rectification. They were
made of glass enclosures containing electrodes in a vacuum.
 Applications: Initially used in radio, television, and early computers.
 Limitations: Vacuum tubes were bulky, consumed a lot of power, generated significant
heat, and had limited reliability.
II. Power Diodes
 1940s: The invention of the semiconductor diode marked the beginning of solid-state
electronics. The first semiconductor diodes were made from germanium.
 1950s: Silicon diodes replaced germanium diodes due to their superior thermal stability
and electrical characteristics.
 Materials: Early diodes used germanium; modern power diodes use silicon.
 Applications: Power rectification in power supplies, battery chargers, and various
electronic circuits.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 11
III. Thyristors
 1957: The silicon-controlled rectifier (SCR), a type of thyristor, was introduced by General
Electric.
 1960s: Other types of thyristors were developed, including TRIACs and DIACs.
 Materials: Thyristors are primarily made from silicon.
 Applications: AC/DC motor control, light dimmers, pressure control systems, and power
switching.
IV. Power Transistors
 1950s: Bipolar Junction Transistors (BJTs) were developed from germanium and later
silicon.
 1960s: The development of the Metal-Oxide-Semiconductor Field-Effect Transistor
(MOSFET) began to revolutionize power electronics.
 1970s: The introduction of Insulated-Gate Bipolar Transistors (IGBTs) combined the best
characteristics of BJTs and MOSFETs.
 Materials:
o BJTs: Initially germanium, later silicon.
o MOSFETs: Silicon, and more recently, silicon carbide (SiC) and gallium nitride
(GaN) for high-performance applications.
o IGBTs: Primarily silicon, with emerging use of SiC for higher efficiency and
thermal performance.
 Applications: Switch-mode power supplies, motor drives, electric vehicles, renewable
energy systems, and various industrial applications.
Materials Used in Power Semiconductor Devices
 Germanium (Ge): Early semiconductor devices, limited by lower thermal conductivity.
 Silicon (Si): The dominant material for most power semiconductor devices due to its
excellent electrical properties, thermal stability, and cost-effectiveness.
 Silicon Carbide (SiC): Used in modern high-performance power devices for its superior
efficiency, high voltage, and high-temperature operation.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 12
 Gallium Nitride (GaN): Emerging material for high-frequency and high-efficiency
applications, such as RF amplifiers and advanced power converters.
Classification of Power Semiconductor Devices
Power semiconductor devices can be broadly classified into two main categories: uncontrolled
(two-terminal) and controlled (three-terminal) devices.
1. Uncontrolled Power Semiconductor Devices (Two-terminal)
Uncontrolled devices are characterized by having only two terminals and cannot be actively
controlled to switch them on or off. These devices conduct whenever a forward voltage is applied
across their terminals.
Examples:
 Power Diodes:
o Conduct when forward biased and block current when reverse biased.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 13
o Used primarily for rectification in power supplies, battery chargers, and various
electronic circuits.
2. Controlled Power Semiconductor Devices (Three-terminal)
Controlled devices have an additional terminal, known as the gate or control terminal, which
allows them to be actively controlled to switch them on or off. This enables precise control over
the flow of current through the device.
Examples:
 Thyristors:
o Silicon-Controlled Rectifier (SCR):
 Conducts when a gate signal is applied and continues to conduct until the
current drops below a certain threshold.
 Commonly used in AC/DC motor control, light dimmers, and power
switching applications.
 Transistors:
o Bipolar Junction Transistors (BJTs):
 Control current flow through the device by varying the base current.
 Widely used in amplification and switching applications.
o Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs):
 Control current flow through the device by varying the gate-source voltage.
 Commonly used in power electronics, such as in switch-mode power
supplies and motor drives.
o Insulated-Gate Bipolar Transistors (IGBTs):
 Combine the high-current capability of BJTs with the voltage control of
MOSFETs.
 Used in high-power applications like motor drives, renewable energy
systems, and traction applications.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 14
Control Characteristics of Power Devices
The control characteristics of power devices refer to their behavior and response to control
signals, which enable precise control and manipulation of electrical power in power electronic
systems.
1. Switching Speed: This refers to how quickly a power device can transition between its ON
and OFF states. Faster switching speeds are desirable in many applications as they minimize
switching losses and improve efficiency. However, excessively fast switching can lead to
issues like electromagnetic interference (EMI) and increased voltage stresses.
sw on off
t = t +t
where tsw is the total switching time, ton is the turn-on time, and toff is the turn-off time.
2. Turn-On and Turn-Off Times: Turn-on time is the duration required for a power device to
switch from the OFF state to the ON state, while turn-off time is the time taken to switch
from the ON state to the OFF state. Minimizing these times helps in reducing switching losses
and improving overall performance.
 Turn-On Time (ton): on d r
t = t +t
where td is the delay time and tr is the rise time.
 Turn-Off Time (toff): off f s
t = t + t
where tf is the fall time and ts is the storage time.
3. Conduction Losses: Power devices exhibit conduction losses when they are in the ON state.
These losses are primarily due to the finite resistance of the device when conducting current.
Lower conduction losses result in higher efficiency.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 15
2
conduction on
P = I ×R
where I is the current through the device and Ron is the on-state resistance of the device.
4. Switching Losses: Switching losses occur during the transition between the ON and OFF
states. They consist of both turn-on and turn-off losses and are caused by the energy required
to charge and discharge the device's capacitance and the time taken to complete these
transitions.
switching DS D on off sw
1
P = V ×I t +t )×f
(
2
where VDS is the drain-source voltage, ID is the drain current, ton is the turn-on time, toff
is the turn-off time, and fsw is the switching frequency.
5. Reverse Recovery Time: In semiconductor devices such as diodes and thyristors, reverse
recovery time refers to the time taken for the device to switch from the conducting state to
the blocking state when the polarity of the applied voltage is reversed. Minimizing reverse
recovery time reduces switching losses.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 16
rr p d
t = t +t
where:
 tp is the storage time, during which the charge carriers recombine and the current remains
constant or decreases slowly, after the forward current has been turned off.
 Td is the fall time, during which the reverse recovery current decreases rapidly to zero.
6. Gate or Base Drive Requirements: Power devices such as MOSFETs, IGBTs, and BJTs
require specific voltage and current levels at their gates or bases to switch them between ON
and OFF states effectively. Understanding these requirements is crucial for proper device
control and reliable operation.
7. Temperature Dependence: The performance of power devices often varies with
temperature. Parameters such as threshold voltage, ON-state resistance, and leakage current
can change significantly with temperature variations. Proper thermal management is essential
to ensure reliable operation under different temperature conditions.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 17
8. Protection Features: Many modern power devices incorporate built-in protection features
such as overcurrent protection, overvoltage protection, and thermal shutdown to safeguard
against abnormal operating conditions and ensure device longevity.
Block Diagram of Power Electronics
The processing or converting of electric power is achieved through a power electronics converter
also known as power converters or switching converters.
1. Source of Electrical Power:
 The origin of the electrical energy supplied to the system. This can be an AC or DC source
such as a battery, solar panel, or AC grid.
 Provides the necessary power for the operation of the entire system.
2. Power Electronic Converter Circuit:
 The core component that converts electrical power from one form to another. This can be
inverters, rectifiers, DC-DC converters, or AC-AC converters.
 Changes the voltage, current, or frequency according to the needs of the load or application.
It also ensures efficient power conversion with minimal losses.
3. Electrical Load:
 The device or component that consumes the electrical power. This can be anything from a
motor, a lamp, a computer, or an entire industrial system.
 The end-user of the electrical power which performs the desired function or operation.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 18
4. Sensor or Sensing Unit or Feedback Circuit:
 Devices that monitor the performance and operational parameters of the power electronics
system, such as current, voltage, temperature, or speed.
 Provides real-time data and feedback to the control unit to ensure the system operates
within desired parameters and to implement protection mechanisms.
5. Control Unit or Controller:
 The brain of the power electronics system, which processes the feedback signals from the
sensors and sends control signals to the converter circuit.
 Regulates the operation of the power electronic converter to maintain the desired output,
implement protection schemes, and optimize performance.
This arrangement ensures that the power electronics system operates efficiently, safely, and meets
the required performance criteria.
Design of Power Electronics Equipment
The design of power electronics equipment can be divided into steps to ensure that electrical
energy is processed and controlled efficiently, meeting the specific requirements of the load.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 19
1. Design of Power Circuits: The design of power circuits involves creating the electrical
pathways and selecting the components (e.g., SCR, MOSFETs, IGBTs) that will handle
the main power flow within the system.
2. Protection of Power Devices: Protecting power devices from electrical, thermal, and
environmental stresses to ensure reliable and safe operation. (e.g., fuses, circuit breakers, or
current sensing circuits)
3. Determination of the control strategy: Designing algorithms such as PWM (Pulse Width
Modulation), Implementing feedback loops that use sensor data to adjust the control signals
and maintain system stability and performance. Deciding whether to use digital controllers
(microcontrollers, DSPs, FPGAs) or analog controllers based on application needs.
4. Design of logic and gating circuits: Designing circuits that provide the necessary voltage
and current levels to switch the power devices on and off efficiently. (e.g., Isolation,
Timing and Synchronization)
Microcontroller based Power Controller
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 20
Comparison of DC Vs. AC, Single-Phase Vs. Three-Phase AC
Parameter DC (Direct
Current)
AC (Alternating
Current)
Single Phase
AC
Three Phase AC
Flow
Direction
One direction Reverses
periodically
Alternates
periodically
Alternates
periodically
Voltage
Source
Constant Varies sinusoidally Sinusoidal
waveform
Three sinusoidal
waveforms, 120°
apart
Power
Distribution
Suitable for low-
voltage
applications
Efficient for long-
distance
transmission
Residential,
small
commercial
Industrial,
commercial, large
motors
Voltage
Regulation
Easier More complex Moderate Moderate to
complex
Typical
Frequency
0 Hz 50 or 60 Hz 50 or 60 Hz 50 or 60 Hz
Phase Angle N/A 0° 0° 120° between
phases
Applications Electronics,
battery-powered
devices
Power distribution,
electric motors
Lighting, small
appliances
Industrial power
distribution, motors
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 21
Types of Power Electronic Circuits/Convertors
Power electronic circuits are mainly classified into main four types
I)AC to DC Converters (Rectifiers)
AC to DC converters, or rectifiers, convert alternating current (AC) to fixed or variable direct
current (DC).
i)Diode Rectifiers(Uncontrolled): Convert AC voltage to a fixed DC voltage.
ii)Phase(Controlled) Rectifiers: Convert AC voltage to a variable DC voltage.
II) DC to DC Converters (Choppers)
DC to DC converters, or choppers, convert a fixed DC input voltage to a variable DC output
voltage.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 22
i) Step-down Chopper (Buck Converter): A step-down chopper, also known as a buck converter,
reduces the input DC voltage to a lower output DC voltage.
ii) Step-up Chopper (Boost Converter): A step-up chopper, also known as a boost converter,
increases the input DC voltage to a higher output DC voltage.
III) DC to AC Converters (Inverters)
DC to AC converters, or inverters, convert fixed DC voltage to variable AC voltage and
Frequency.
i)Voltage Source Inverters (VSI): The input is a fixed DC voltage source.
o Single-Phase VSI: Used in UPS systems and small-scale renewable energy
systems.
o Three-Phase VSI: Employed in industrial motor drives and grid-tied renewable
energy systems.
ii)Current Source Inverters (CSI): The input is a fixed DC current source.
o Single-Phase CSI: Less common, used in specific industrial applications.
o Three-Phase CSI: Used in large motor drives and industrial applications.
IV)AC to AC Converters
AC to AC converters change AC power from one form to another.
i)Cycloconverters: Convert AC supply of fixed voltage and frequency to AC output of variable
voltage and frequency.
o Single-Phase to Single-Phase Cycloconverters
o Three-Phase to Single-Phase Cycloconverters
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 23
o Three-Phase to Three-Phase Cycloconverters
Applications: Used in slow-speed large AC traction drives, rotary kilns, and multi-megawatt AC
motor drives.
ii)AC Voltage Controllers (AC Voltage Regulators): Change AC voltage while maintaining
the same frequency.
o Single-Phase AC Voltage Controllers: Common in lighting control and small
motor speed control.
o Three-Phase AC Voltage Controllers: Used in electronic tap changers and
speed control of large fans and pumps.
Comparison of Power Electronic Circuits/Converters
Converter
Type
Sub-Type Function Applications
I)AC to DC
Converters
(Rectifiers)
i)Diode Rectifiers
(Uncontrolled)
Convert AC voltage to
a fixed DC voltage
Battery charging, power
supplies, welding, UPS
systems, electric traction,
electroplating
ii)Phase-Controlled
Rectifiers
Convert AC voltage to
a variable DC voltage
DC drives, HVDC systems,
excitation systems,
metallurgical, chemical
industries, compensators
II)DC to DC
Converters
(Choppers)
i)Step-down Chopper
(Buck Converter)
Reduce input DC
voltage to a lower
output DC voltage
Voltage regulation, battery
charging, low-voltage DC
motor drives
ii)Step-up Chopper
(Boost Converter)
Increase input DC
voltage to a higher
output DC voltage
Power factor correction,
electric vehicles, renewable
energy systems
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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III)DC to AC
Converters
(Inverters)
i)Voltage Source
Inverters (VSI)
Convert fixed DC
voltage to variable AC
voltage and frequency
UPS systems, small-scale
renewable energy systems,
industrial motor drives, grid-
tied renewable energy systems
ii)Current Source
Inverters (CSI)
Convert fixed DC
current to variable AC
voltage and frequency
Large motor drives, industrial
applications
IV)AC to AC
Converters
i)Cycloconverters Convert fixed AC
voltage and frequency
to variable AC voltage
and frequency
Slow-speed large AC traction
drives, rotary kilns, multi-
megawatt AC motor drives
ii)AC Voltage
Controllers (AC
Voltage Regulators)
Change AC voltage
while maintaining the
same frequency
Lighting control, small motor
speed control, electronic tap
changers, speed control of
large fans and pumps
Power Transistors
 Power transistors are three-terminal semiconductor devices designed to handle high
currents and voltages.
 Power transistors are fully controlled devices. This means they can be turned ON and OFF
by applying an appropriate control signal.
 They are categorized into three main types:
I)Power Bipolar Junction Transistors (BJTs)
II)Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), and
III)Power Insulated-gate bipolar transistors (IGBTs).
 Each type has its unique characteristics and applications.
I)Power BJTs
 Power BJTs, also known as bipolar junction transistors (BJTs), are three-terminal
semiconductor current controlled devices that use both electrons and electron holes as
charge carriers.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 A Power BJTs are designed to handle high current and voltage levels, making it suitable
for power applications.
 Presently power BJTs are available with ratings up to 1200 V, 800 A, with a maximum
switching frequency of 10 kHz.
 Because of higher mobility of electrons when compared with holes, n-p-n devices can be
fabricated on a smaller silicon area to provide the same performance as an equivalent p-n-
p device. So, the usage of n-p-n type of power BJT is more common in power electronics
than p-n-p type.
 Power BJTs can act as switches, amplifiers, or oscillators, depending on the biasing
conditions
Construction of Power BJT:
 It consists of alternating P and N-type layers, with a drift region added to enhance its power
handling capabilities. This region is characterized by a low doping level of approximately
10^14 cm^-3 and is responsible for the transistor's ability to handle high currents and
voltages
 The thickness of the dirft region determines the breakdown voltage of the Power transistor.
 The characteristics of the device is determined by the doping level in each of the layers and
the thickness of the layers.
 The three terminals are the emitter (E), base (B), and collector (C).
 Emitter (E): Highly doped with a high concentration of charge carriers, , typically
0.1-10μm.
 Base (B): Lightly doped with a low concentration of charge carriers, typically 5-20
μm.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 Collector (C): Moderately doped with a concentration of charge carriers between
that of the emitter and base, typically 50-200 μm.
 The structure of a Power BJT is different from a signal-level transistor, with a four-layer
structure of alternating P and N-type doping
 The key differences in construction are:
 Heavily doped n+ and p+ regions are used to carry large currents with minimal
voltage drop
 A lightly doped drift region is added between the collector and base to support high
voltages in the off-state
Steady State Characteristics of Power BJT
Based on the forward and reverse bias condition of the power transistor, it operates in four regions.:
Cut off region, Active region, Quasi saturation region, Hard saturation region
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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1)Cut off region (OFF Switch)
 In this region, both the base-emitter junction and the base-collector junction are reverse-
biased.
 The region below the characteristic for IB=0 is cut-off region. In this region, BJT offers
large resistance to the flow of current. Hence it is equivalent to an open circuit.
 In the cut-off region, the BJT is essentially off. There is no significant current flowing from
collector to emitter.
 Base current (IB): IB=0
 Collector current (IC): IC≈0 (leakage current)
 Collector-Emitter voltage (VCE ): VCE≈VCC
2)Active region/Liner Zone(Amplifier)
 In the active region, the BJT operates as an amplifier. The base-emitter junction is forward-
biased, and the base-collector junction is reverse-biased.
 If BJT uses as an amplifier, it operates in this region. The dynamic resistance in this region
is large. The power dissipation is maximum.
 Collector current (IC): C B
I I

 , where β is the current gain of the transistor.
 Collector-Emitter voltage (VC): ( )
CE CE sat
V V

3)Quasi saturation region (Partially Saturation)
 Quasi-saturation region is between the hard saturation and active region. This region exists
due to the lightly doped drift layer.
 In the quasi-saturation region, the transistor is partially saturated. This region occurs before
full saturation, and the base-collector junction is not fully forward-biased.
 When the BJT operates at high frequency, it is operated in this region. Both junctions are
forward bias. The device offers low resistance compared to the active region.
 So, power loss is less. In this region, the device does not go into deep saturation. So, it can
turn off quickly. Therefore, we can use for higher frequency applications.
 Collector-Emitter voltage (VCE): ( )
CE sat
V VCE V
 
 Base current (IB): Sufficiently high to keep the transistor out of the hard
saturation region.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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4)Hard saturation region (Deep Saturation)
 The Power BJT push into the hard-saturation region from the quasi-saturation region by
increasing the base current. This region is also known as deep saturation region.
 The resistance offers in this region is minimum. It is even less than the quasi-saturation
region. So, when the BJT operates in this region, power dissipation is minimum.
 The device acts as a closed switch when it operates in this region. But it needs more time
to turn off. So, this region is suitable only for low-frequency switching application.
 In this region, both junctions are forward bias. The collector current is not proportional to
the base current, IC remains almost constant at IC(sat) and independent from the value of
base current.
Primary and Secondary Breakdown in Power BJT
Primary Breakdown:
 Primary breakdown occurs due to excessive voltage across the collector-emitter junction,
leading to avalanche breakdown.
 This occurs when the collector-emitter voltage (VCE) exceeds the maximum rated voltage
(VCEO) of the transistor.
 Avalanche Breakdown Condition: CE CEO
V V

ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 The breakdown voltage mechanism involves the transistor gain and the breakdown
phenomenon in the PN junction.
Secondary Breakdown:
 Secondary breakdown occurs due to a combination of high voltage and high current,
resulting in localized heating and thermal runaway.
 It is characterized by the collapse of the collector-emitter voltage under high power
dissipation conditions.
 Secondary Breakdown Condition: ( )
CE C max
V I PD
 
The Safe Operating Area (SOA) of the BJT is typically defined to prevent these breakdowns,
ensuring that the device operates within safe limits of voltage, current, and power dissipation.
II)Power MOSFETs
 Power MOSFETs are enhancement mode voltage controlled majority carrier devices
having three terminals namely, source (S), gate (G), and drain (D) used for low power high
frequency switching applications (a few kW and 100s of kHz).
 As a majority-carrier device, the MOSFET operates at much higher speed than BJT
because there is no charge-storage mechanism. MOSFETs need continuous application of
gate-to-source voltage to remain in the conducting state. MOSFETs do not suffer from
second breakdown as BJTs do.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 Under steady-state conditions the gate draws very small current of the order of nano-
amperes.
 But, during turn-ON and turn-OFF it could be higher because of charging and discharging
of the gate capacitance.
 MOSFETs have very short switching times. Their ON-state resistance Rosin„) has positive
temperature coefficient. So parallel operation of MOSFETs is simpler when compared to
the parallel operation of BJTs.
 Power are widely used in power electronics due to their high efficiency, fast switching
speeds, and ease of drive.
Enhancement Mode MOSFETs
 Enhancement mode MOSFETs require a gate-to-source voltage (VGS) to be applied in
order to turn on and conduct current between the drain and source.
 In other words, the MOSFET is normally off when VGS is zero and only turns on when
VGS exceeds a certain threshold voltage (Vth).
Characteristics of Enhancement Mode MOSFETs
 Normally Off: With no voltage applied to the gate, the device remains off, and there is no
conduction path between the drain and source.
 Threshold Voltage (Vth): The minimum gate-to-source voltage required to form a
conductive channel between the drain and source.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 Positive VGS (for n-channel) or Negative VGS (for p-channel): A positive VGS for an
n-channel MOSFET or a negative VGS for a p-channel MOSFET is needed to turn the
device on.
Depletion Mode vs. Enhancement Mode MOSFETs
 Default State: Depletion mode MOSFETs are normally on (=0), while enhancement mode
MOSFETs are normally off (=0).
 Leakage Current: Depletion mode MOSFETs have higher leakage currents in the off
state, whereas enhancement mode MOSFETs have lower leakage currents in the off state.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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Comparison Depletion Mode between Enhancement Mode MOSFETs
Feature Depletion Mode MOSFET Enhancement Mode MOSFET
Default State Normally On VGS=0 Normally Off VGS=0
Threshold Voltage
(Vth)
Negative (n-channel Positive (n-channel)
Gate Control Negative VGS to turn off (n-
channel)
Positive VGS to turn on (n-
channel)
Applications Used in analog switches, depletion
load devices
Widely used in digital and power
applications
Control Less common, harder to control
precisely
More common, easier to control
precisely
Switching Speed Generally slower Generally faster
Leakage Current Higher in off state Lower in off state
Why Power MOSFETs are Typically Enhancement Mode?
 Fail-Safe Operation: Enhancement mode MOSFETs are normally off, providing a safer
default state in the absence of a control signal.
 Efficiency: They have lower leakage currents when off, improving overall efficiency.
 Control and Drive Simplicity: Require a single polarity drive voltage for operation,
simplifying the gate drive circuitry.
 Thermal Management: Easier to manage heat dissipation due to precise control over the
on-state resistance (RDS(on)).
 Design and Fabrication: More straightforward to design and fabricate for high-power and
high-frequency applications.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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Construction of Power MOSFET
 Power MOSFETs are built using a p-type substrate with heavily doped n+ source and drain
regions. Over the channel region, a thin insulating layer of SiO2 is formed, and an
aluminum layer serves as the gate.
 To enhance the voltage rating, a lightly doped n- drift layer is included. This drift layer,
along with the vertically oriented structure of alternating p and n layers, minimizes the
current flow area, reducing on-state resistance and losses. The p-type middle layer, called
the "body," and the n- "drift region" collectively determine the MOSFET's breakdown
voltage.
 The different types of power MOSFET have different attributes and therefore can be
particularly suited for given applications.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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Type Structure Advantages Applications
1. Planar
MOSFET
Basic form High voltage ratings,
dominated by epi-layer
resistance
High voltage
applications
2. VMOS V-groove structure Lower ON resistance, better
switching characteristics
Power switching, small
RF power amplifiers
3. UMOS Flattened groove Lower ON resistance, improved
packing density, higher current
density, better efficiency and
reliability compared to VMOS
Power switching
4. HEXFET Hexagonal structure Increased current capability Power applications
5. TrenchMOS Trench structure Better handling capacity and
characteristics, lower ON
resistance for voltages above
200 volts
High voltage
applications
Device Operation of Power MOSFET
Power MOSFET is a minority carrier device. So, conduction takes place only by the electrons.
Therefore, the conduction cannot take place through the MOSFET from the drain to source due to
the presence of P-layer in between. But this is possible by Inversion layer creation.
Operation Phases:
1. Formation of the Depletion Region:
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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 The MOSFET is forward biased by connecting a positive voltage to its drain terminal with
respect to source terminal and the gate is made positive with respect to the body layer.
 The "P" layer of consists of a large number of holes and few electrons. The holes are
majority carriers. Hence they outnumber the electrons which are minority carriers, still the
number of electrons present in the "P" layer is sufficiently large.
 Due to the positive voltage applied between gate body these electrons are attracted towards
the gate and gather below the SiO2 layer and produce depletion layer by combining with
the holes that are present there.
Creation of the Inversion Layer (Induced Channel):
 If the positive gate voltage is increased further, the number of electrons below the
SiO2 layer will be greater than the number of holes.
 Thus the conductivity of the part of P layer close to SiO2 layer will change from positive
to negative. That means an n type of sub layer is formed below the SiO2 layer.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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• This process is known as creation of the inversion layer, and the process of generation of
an inversion layer due to the externally applied gate voltage is known as the "field effect”.
• The inversion layer is also called as the induced channel. This induced channel will
connect the two n+
layers on either sides of the p-region.
• In this way now the n type channel gets created in the P type body layer and conduction
can take place through this layer.
• The resistance of the induced channel is dependent on the magnitude of gate to base (body)
voltage. Higher the gate voltage less is the resistance. The MOSFET acts as a variable
resistor.
• With increase in the gate to body voltage, the resistance will decrease. However, this
resistance cannot decrease below a certain minimum value even with increase in the gate
to body voltage.
• If the maximum specified value of gate voltage is exceeded, then the SiO2 layer will
breakdown.
MOSFET Characteristics (Transfer, Output and Switching Characteristics)
An n-channel Enhancement-type MOSFET allows current to flow from the drain to the source by
applying a voltage to the gate.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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a) Transfer Characteristics
 The transfer characteristics show the relationship between the drain current (IDS) and the
gate-to-source voltage (VGS) for a constant drain-to-source voltage (VDS).
 Below Threshold Voltage (VGS < VT): No current flows (IDS = 0) because the channel
is not formed.
 Above Threshold Voltage (VGS > VT): Current (IDS) increases as VGS increases. This
region shows how the MOSFET turns on and how the gate voltage controls the drain
current.
b) Output Characteristics
 The output characteristics show the relationship between the drain current (IDS) and the
drain-to-source voltage (VDS) for various gate-to-source voltages (VGS).
 Cut-off Region (VGS < VT): No current flows (IDS = 0) regardless of VDS.
 Ohmic Region (Linear Region): For VGS > VT and low VDS, IDS increases linearly
with VDS, and the MOSFET behaves like a variable resistor.
 Saturation Region: At higher VDS, IDS levels off and becomes almost constant,
determined by VGS. This region is also called the active region.
c)Switching Characteristics
 The switching characteristics of an n-channel Enhancement-type MOSFET describe how
quickly and efficiently the MOSFET can turn on and off.
 The turn-on & turn-off times of the MOSFET get affected by its internal capacitance and
the internal impedance of the gate drive circuit. But these internal capacitances have no
effect during steady state operation.
 These characteristics are crucial for applications in switching power supplies, digital
circuits, and other high-speed switching applications.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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Switching Process
1. Turn-On Process:
o Initial State: The MOSFET is off with no current (=0) flowing between the drain and
source.
o Gate Voltage Applied: When a positive gate-to-source voltage (VGS) is applied, the
gate-to-source capacitance (Cgs) starts to charge.
o Turn-on Delay (td(on)): This is the time taken for the gate voltage to reach the threshold
voltage (VT) and start forming the channel.
( )
( )
( )
1 g gs
t
R C
G
GS t
V V e

 
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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o Rise Time (tr): Once VGS exceeds VT, the channel forms quickly, and IDS rises to its
maximum value.
2
( )
2
T
GS
DS
V V
I
K


o The total turn-on time (ton) is the sum of the turn-on delay and the rise time:
on r
d(
= t on)
t +t
2. Turn-Off Process:
o Initial State: The MOSFET is on with current (IDS) flowing between the drain and
source.
o Gate Voltage Removed: When the gate voltage is removed, the gate-to-source
capacitance (Cgs) starts to discharge.
o Turn-off Delay (td(off)): This is the time taken for VGS to fall below the threshold
voltage (VT). During this period, the channel starts to collapse.
( )
( )
g gs
t
R C
G
GS t
V V e


o Fall Time (tf): Once VGS drops below VT, the channel collapses quickly, and IDS falls
to zero.
( )
0
( )
t
RgCgs
DS D
I t I e

 , where ID0 is the initial current.
o The total turn-off time (toff) is the sum of the turn-off delay and the fall time:
f
(
t = t off + t
Of
)
f d
Factors Affecting Switching Characteristics
 Gate Capacitance: Higher capacitance results in slower switching times due to longer
charging and discharging periods.
 Gate Resistance: Higher resistance increases the time constants for charging and
discharging the gate capacitance, slowing down the switching speed.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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 Driver Strength: Stronger gate drivers can provide higher current to charge and discharge
the gate capacitance faster, improving switching speed.
 Parasitic Inductances: Inductances in the circuit can cause delays and ringing during
switching transitions, affecting the overall performance.
III) Power IGBTs
 IGBT is a three terminal device having a collector (C), emitter (E), and the gate (G). The
collector and emitter are the power terminals. Gate and emitter are the control terminals.
An IGBT has the merits of both BJT and MOSFET.
 They combine the high input impedance and fast switching of MOSFETs with the high-
voltage and high-current capabilities of bipolar junction transistors (BJTs). i.e., IGBTs are
composite devices that combine the input characteristics of a MOSFET with the output
characteristics of a BJT.
 IGBT does not have any second breakdown problem like a BJT.
 An IGBT can also be designed to block negative voltages. This is not possible in the case
of BJTs and MOSFETs.
 IGBTs have come closer to the 'ideal switch', with typical voltage ratings of 600 - 1700
volts, ON-state voltage of 1.7 - 2.0 volts at currents of up to 1000 amperes, and switching
speeds of 200 - 500 ns.
 The availability of IGBTs has lowered the cost of systems and enhanced the number of
economically practical applications.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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Construction of IGBT
Similar to MOSFET, the vertically oriented structure of an IGBT is designed to maximize the area
available for current flow, reducing the resistance and on-state power loss.
P+ Injection Layer (Drain Layer): This layer forms the drain of the IGBT and is responsible for
injecting holes into the N- drift region, enhancing conductivity and current flow.
N+ Buffer Layer: This layer serves two important purposes:
 Reducing On-State Voltage Drop: The N+ buffer layer helps to reduce the voltage
drop across the device when it is in the on-state, improving its efficiency.
 Shortening Turn-Off Time: The N+ buffer layer also helps to shorten the turn-off
time of the IGBT, enhancing its switching performance.
N- Drift Region: This layer is designed to improve the breakdown voltage capacity of the IGBT.
It is similar to the structure used in power MOSFETs.
P-Type Base/Gate: The P-type base is heavily doped to reduce resistance and improve the
switching performance of the IGBT.
N-Type Collector and Emitter: The N-type collector and emitter are also heavily doped to
enhance the current-carrying capacity of the IGBT.
Gate-Source Structure: The IGBT uses a highly interdigitated gate-source structure to reduce the
possibility of source/emitter current crowding, ensuring more efficient current flow.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Device Operation of IGBT
The principle of operation of IGBT is similar to that of a MOSFET. The operation can be divided
into two parts:
i)Creation of Inversion Layer
 Similar to MOSFETs, the operation of an IGBT begins with the application of a positive
voltage between the gate and the source (VGS).
 When VGS exceeds the threshold voltage (Vth), an inversion layer is formed beneath the
oxide layer, inducing an N-type channel in the P-type body region. This allows the flow of
current from the collector to the emitter.
ii) Conductivity Modulation
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Conductivity Modulation:
 Unlike MOSFETs, IGBTs exhibit conductivity modulation, a process that reduces on-state
losses. During the device's ON state, carriers (electrons) are injected from the emitter into
the N- drift layer, reducing its resistance.
 This injection of carriers increases the conductivity of the drift region, effectively lowering
the on-state voltage drop across the device.
Double Injection Mechanism:
 The conductivity modulation process involves a phenomenon known as "double
injection."
 Electrons are injected from the heavily doped N+ emitter region (J1) into the N- drift layer
(J3) when junction J3 is forward biased.
 Simultaneously, holes are injected from the P+ layer into the N+ buffer layer (J2), creating
a double injection of carriers into the N- drift region.
 This double injection of electrons and holes enhances the conductivity of the N- drift
region, effectively reducing its resistance and improving the overall performance of the
IGBT.
Output and Transfer Characteristics of IGBT
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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i)Transfer Characteristics
 The transfer characteristics of an IGBT describe the relationship between the gate-emitter
voltage (VGE) and the collector current (IC) while keeping the collector-emitter voltage
(VCE) constant.
 when VGE is below the threshold voltage (VGET), the device remains in the off state, and
IC is practically zero.
 As VGE exceeds VGET, the IGBT enters the active region, and IC starts to increase.
ii) Output Characteristics
The transfer characteristics of IGBT illustrate the relationship between input voltage, VGE, and
output collector current, IC.
 When VGE is 0V, the device remains off with no IC, and when VGE slightly increases but
stays below VGET, it remains off but may exhibit a leakage current.
 Once VGE surpasses the threshold, IC begins to rise, turning the device on. As a
unidirectional device, current flows in only one direction.
 The relationship between collector current, IC, and collector-emitter voltage, VCE, at
different VGE levels.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 At VGE < VGET the GBT is in cutoff mode, resulting in IC = 0 at any VCE. Beyond VGE
> VGET, the IGBT enters the active mode, where IC increases with rising VCE.
Comparison of Power (BJTs), Power (MOSFETs) and IGBTs
Characteristic Power BJT Power MOSFET IGBT
Voltage Rating High < 1kV High < 1kV Very High > 1kV
Current Rating High < 500 A Low < 200 A Very High > 500 A
Frequency Medium High Medium to High
Secondary
Breakdown
Yes No No
Input Drive Circuitry Complex Simple Simples
Input Impedance Low High High
Output Impedance Low Medium Low
Switching Loss High Low Medium
Switching Speed Low Fast Medium
Cost Low Medium High
Power Applications General purpose, high
power, audio
amplification
Low voltage, high
frequency applications,
DC-DC converters,
motor drives
Motor drives, inverters,
UPS systems,
renewable energy
systems
Thyristors
 Thyristors are a type of semiconductor device that can be used to control the flow of
electrical current, used for rectification and switching in high-power circuits.
 The most common type of thyristor is the Silicon-Controlled Rectifier (SCR)
 The word Thyristor is formed from two words thyratron and transistor.
 Besides, the characteristics possessed by a thyristor is the combination of the properties of
thyratron and transistor.
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 The thyratron has the property of rectification and the transistor has the property of
switching.
 The thyristors are turned on using the control signal transferred by the transistor. Unlike
the diodes, the thyristors have three terminals Anode, Cathode and Gate terminal.
 SCRs typically handle voltages from a few volts up to 10kv and currents
from a few milliamperes up to 1.5kA which respond to 15MW power
handling capacity.
 Thyristors are widely used in applications such as motor control, light
dimmers, and pressure control systems.
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Construction of SCR
 It consists of four layers of alternating p-type and n-type materials, forming a PNPN.
 The SCR has four layers of extrinsic semiconductor materials, which form three PN
junctions named J1, J2, and J3.
The SCR has three junctions:
J1: Between the p-type outer layer and the n-type outer layer.
J2: Between the p-type inner layer and the n-type inner layer.
J3: Between the p-type inner layer and the n-type outer layer.
 The anode and cathode terminals are placed at the end layers, and the gate terminal is
placed with the third layer. The outer layers are heavily doped, and the inner two layers are
lightly doped.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Principle of Operation of SCR
 The operation of SCR is divided into two categories,
i) When Gate is open and ii) When Gate is closed.
i)When gate is open:
 Consider that the anode is positive with respect to cathode and gate is open. • The junctions
Ji and 13 are forward biased and junction J2 is reverse biased.
 There is depletion region around J2 and only leakage current flows which is negligibly
small.
 Practically the SCR is said to be OFF. This is called forward blocking state of SCR and
voltage applied to anode and cathode with anode positive is called forward voltage.
Forward Blocking State Reverse Blocking State
 With gate open, if cathode is made positive with respect to anode, the junctions J1, J3
become reverse biased and J2 forward biased. Still the current flowing is leakage current,
which can be neglected as it is very small.
 The voltage applied to make cathode positive is called reverse voltage and SCR is said to
be in reverse blocking state.
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 In forward blocking state, if the forward voltage is increased and made sufficiently large,
the reverse biased junction J2 breaks down and SCR conducts heavily. This voltage is
called forward break over voltage VB0 of SCR. In such condition, SCR is said to be ON
or triggered.
ii)When gate is closed:
 Consider that the voltage is applied between gate and cathode when the SCR
is in forward blocking state.
 The gate is made positive with respect to the cathode.
 The electrons from n-type cathode which are majority in number, cross the
junction .13 to reach to positive of battery.
 While holes from p type move towards the negative of battery, this constitutes
the gate current.
 This current increases the anode current as some of the electrons cross
junction 12. As anode current increases, more electrons cross the junction J2
and the anode current further increases.
 Due to regenerative action, within short time, the junction J2 breaks and SCR
conducts heavily. The resistance R is required to limit the current.
 Once the SCR conducts, the gate loses its control.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Static Anode- Cathode Characteristics of SCR
 The static anode-cathode characteristics of an SCR (Silicon-Controlled Rectifier) describe
the relationship between the anode current (IA) and the anode-cathode voltage (VAK)
under different conditions.
 The static characteristic is divided into three modes:
1. Forward Blocking mode
2. Forward conduction mode
3. Reverse Blocking mode
Static V-I Characteristics
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1. Forward Blocking mode:
 VAK>0 (positive voltage applied to the anode relative to the cathode), Gate is not
triggered.
 When anode is at a higher potential than cathode, thyristor is said to be forward biased, It
is seen from the figure that when the gate circuit is open J1 and J3 are forward biased and
junction J2 is reverse bias.
 In this mode a small current, called forward leakage current flows from anode to cathode.
 OM represents the forward blocking mode of SCR
 SCR is treated as an open switch in the forward blocking mode.
2. Forward Conduction mode:
 VAK>0 (positive voltage applied to the anode relative to the cathode), Gate is triggered.
 When anode to cathode forward voltage is increased with gate circuit open, reverse biased
junction J2 will have an avalanche breakdown at a voltage called forward break over
voltage VBO.
 After this breakdown, thyristor gets turned ON with point 'M' at once shifting to 'N'. Here
NK represents the forward conduction mode.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 A thyristor can be brought from forward blocking mode to forward conducting mode by
applying.
 A positive gate pulse between gate and cathode or
 A forward breakover voltage VBO across anode and cathode.
 Voltage drop across the SCR 'VT' increases slightly with an increase in anode current. It
can be seen from NK.
Latching Current:
 It is defined as the minimum value of anode current which it must attain during turn-on
process to maintain conduction when gate signal is removed.
 The gate pulse width should be chosen to ensure that the anode current rises above the
latching current.
Holding Current:
 It is defined as the minimum value of anode current below which the SCR gets turned off.
 Latching current is more than Holding current.
 Latching current is associated with turn on process.
 Holding current is associated with turn off process.
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3. Reverse Blocking mode:
 VAK<0 (negative voltage applied to the anode relative to the cathode).
 When cathode is made high potential with respect to anode with gate open, then the SCR
is said to be reverse biased.
 J1 and J3 are reverse biased and J2 is forward biased.
 A small current flows through the SCR this is called as reverse leakage current.
 This is reverse blocking mode, called the OFF state of the SCR.
 If the reverse voltage increased, then at reverse breakdown voltage VBR, an avalanche
breakdown occurs at J1 and J3 and the reverse current increases rapidly PQ.
 The SCR in the reverse blocking mode may therefore be treated as an open switch.
Two transistor model of SCR
 The two transistor model of SCR is a simplified representation of the device's operation,
which combines the p and n layers into two interconnected transistors: one PNP and one
NPN.
 This model helps to explain the SCR's behavior and is useful for analyzing its operation.
 The two-transistor model of an SCR (Silicon-Controlled Rectifier) consists of an NPN
transistor (T2) and a PNP transistor (T1) connected back-to-back.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Structure:
 T1 (PNP): Base connected to T2's collector.
 T2 (NPN): Base connected to T1's collector.
 G: Gate terminal.
 A: Anode terminal.
 K: Cathode terminal.
Operation:
 When switch S is closed, a positive pulse is applied to the base of T2 (NPN).
 T2 (NPN) starts conducting, creating a short circuit between its collector and emitter,
bringing the negative terminal voltage to the base of T1 (PNP).
 This negative voltage causes T1 (PNP) to conduct as well.
 Both transistors T1 and T2 conduct, forming a short-circuited path and allowing current to
flow from the supply voltage V through the load resistor R.
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Mathematical Analysis of the two-transistor model
According to the transistor leakage current equation, the collector current is given as
Therefore, for the first transistor T1, we can say,
As for the first transistor, the emitter current equals to the anode current Ia.For the second transistor,
T2
As the emitter current in the case of the second transistor is equal to the cathode current of the
second transistor Ik.
By applying KCL in the circuit, we can say,
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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Again, by applying KCL, we can say
Therefore, Ia can be given as
Hence,
 If in equation (α1 + α2) =1, -IA =∞
 SCR suddenly latches to the ON state from OFF state condition, this characteristic of
device is called regenerative action.
 Once the SCR goes into conduction, the two transistor model is no more applicable. Here
note that the internal regeneration takes place in the SCR due to avalanche breakdown of
reverse biased junction J2.
 It does not take place when SCR is reverse biased. When the current through the SCR falls
below holding current, the forward blocking state is regained. Then α1 and α2 of transistors
are also reduced to small values.
Gate Characteristics of SCR
The gate characteristics of an SCR (Silicon-Controlled Rectifier) refer to the relationship between
the gate current (IG) and the gate-cathode voltage (VGK), as well as how these parameters
influence the SCR's operation.
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Turn-ON Methods and Turn-OFF Methods of SCR
The turn-on and turn-off mechanisms of thyristors, particularly silicon-controlled rectifiers
(SCRs), are crucial for their proper operation in various electronic circuits. This response will
cover the different methods of turning on and off SCRs.
I) Turn-ON Methods for SCRs (SCR Triggering)
 Turning on an SCR involves initiating conduction between the anode and cathode, allowing
current to flow through the device. The SCR remains in the off state (blocking state) until
it is properly gate triggered.
 The SCR can be made to conduct or switched from blocking (non-conducting or OFF) state
to Conduction (ON) State by any one of the following methods.
The main methods to turn on an SCR are:
1. Forward Voltage Triggering
2. Gate Triggering
3. dv/dt Triggering
4. Thermal Triggering
5. Light Triggering
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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1. Forward Voltage Triggering
 In forward voltage triggering, the SCR is turned on by applying a voltage across the anode
and cathode that exceeds the breakover voltage (VBO). This method utilizes the intrinsic
properties of the SCR's junctions.
 When the applied voltage (VAK) exceeds the breakover voltage, the depletion region at
the junction breaks down, causing a large current to flow through the SCR.
 The condition for forward voltage triggering is: AK BO
V V

where VAK is the anode-to-cathode voltage and VBO is the breakover voltage.
 Once VBO, the SCR enters into the conduction state and remains on as long as the current
through it is above the holding current (IH).
2. Gate Triggering
 Gate triggering is the most common and practical method to turn on an SCR. It involves
applying a small positive current to the gate terminal with respect to the cathode while the
anode is positive.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 A gate current (IG) injects charge carriers into the base region of the SCR, initiating the
conduction process.
 The SCR turns on if the gate current IG is above a certain threshold : G GT
I I

 The anode current (IA) increases as the gate current IG is applied, reducing the forward
blocking voltage and allowing the SCR to turn on.
3. dv/dt Triggering
 This method relies on a rapid rate of rise of the anode-to-cathode voltage (dv/dt) to turn on
the SCR.
 In this type of triggering, whenever the SCR is in forwarding bias, then two junctions like
J1 & J3 are in forwarding bias and J2 junction will be in reverse bias. Here, J2 junction
performs like a capacitor because of the existing charge across the junction. If the ‘V’ is
the voltage across the SCR, then the charge (Q) and capacitance can be written as
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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0
( )
When
C
C
I
dQ
dt
Q CV
d CV dV dC
dt dt
d
I c v
d
C
t
dt

 


 

 The induced current due to dv/dt is given by: AK
C
dV
I C
dt

where C is the junction capacitance and AK
dV
dt
is the rate of change of the anode-to-cathode
voltage.
 Thus, as the change of voltage rate across the SCR turns into high or low, then the SCR
may trigger.
 If this induced current exceeds the latching current of the SCR, it will turn on.
4. Thermal Triggering
 Thermal triggering involves increasing the junction temperature to reduce the breakover
voltage.
 Increasing temperature reduces the bandgap energy, thereby reducing the breakover
voltage and allowing the SCR to turn on at a lower applied voltage.
0
0
( ) ( ) ( )
BO BO
V T V T T T

  
where VBO(T) is the breakover voltage at temperature VBO(T0) is the breakover voltage
at a reference temperature T0, and α is the temperature coefficient.
 As the temperature increases, VBO decreases, leading to forward voltage triggering at a
lower applied voltage.
 However, in certain circumstances, an SCR can be unintentionally triggered by an external
voltage transient or rapid voltage rise (dv/dt).
 Unintentional dv/dt triggering can be a problem in SCR applications because it may lead
to unexpected or premature triggering, causing the SCR to conduct when it shouldn't,
leading to potential issues like false triggering or damage to the device.
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5. Light Triggering
 When the SCR is triggered with the radiation of light is named as LASCR or Light
Activated SCR. This kind of triggering is used for converters which are controlled by phase
within HVDC systems. In this technique, intensity and light emissions with suitable
wavelength are permitted to hit the J2 junction.
 Light triggering uses photon energy to generate electron-hole pairs in the junction of the
SCR.
 When the SCR is exposed to light, photons impart energy to the electrons, creating
electron-hole pairs. These charge carriers reduce the barrier potential, initiating conduction.
 The number of generated electron-hole pairs depends on the intensity of the incident light
and can be approximated by:
L L
I P

 
where IL is the photocurrent, η is the quantum efficiency, and PL is the incident light
power.
 If the photocurrent ILI_LIL is sufficient to exceed the latching current, the SCR will turn
on.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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II)Turn-OFF Methods for SCRs
 Turning off an SCR involves stopping the current flow through the device, bringing it back
to the off state.
 The SCR naturally stays on as long as the current through it remains above a certain
threshold called the holding current.
 The methods to turn off an SCR are primarily focused on reducing this current below the
holding current.
Commutation:
 Commutation of SCRs refers to the process of turning off the SCR.
 Commutator switches are essential for the operation of DC machines, providing reliable
and straightforward methods for current reversal and rectification.
The main turn-off methods are:
i) Natural Commutation (Line Commutation)
ii) Forced Commutation
i) Natural Commutation (Line Commutation)
 Natural commutation, also known as line commutation, takes advantage of the natural
zero-crossing of the AC supply voltage. This method is inherently used in AC circuits
where the current naturally passes through zero during each half cycle.
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 In an AC circuit, the current through the SCR will naturally drop to zero at the end of
each half cycle. When the current through the SCR falls below the holding current
(IH), the SCR turns off.
 The condition for natural commutation is: A H
I I

where IA is the anode current and IH is the holding current.
 During each zero-crossing of the AC waveform, the anode current reduces to zero,
thus turning off the SCR.
ii) Forced Commutation
 Forced commutation is used in DC circuits or in AC circuits where natural
commutation is not possible.
 It involves externally forcing the current through the SCR to zero using additional
circuitry.
 Forced Commutation is classified into different types. They are:
Class A –Commutation
Class B –Commutation
Class C – Complementary Commutation
Class D – Auxiliary Commutation
Class E – Pulse Commutation
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a) Class A Commutation (Load Commutation)
 Class A commutation uses an LC circuit in parallel with the load to force the current
through the SCR to zero.
 The SCR is connected in series with the load, and an LC resonant circuit is placed in
parallel with the load.
Operation:
 When the SCR is conducting, the load current flows through it.
 The LC circuit is charged during this period.
 Once the LC circuit is fully charged, it starts discharging, creating a reverse current that
opposes the load current.
 This reverse current forces the total current through the SCR to drop below the holding
current, thus turning it off.
 The resonant frequency of the LC circuit is given by:
1
LC
 
where L is the inductance and C is the capacitance.
 The current in the LC circuit can be described by: ( ) ( )
LC m
I t I sin t


where Im is the peak current.
 The condition for turning off the SCR is: total load LC H
I I I I
  
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b) Class B Commutation (Resonant Pulse Commutation)
 Class B commutation employs a resonant LC circuit connected across the SCR to create
an oscillatory current that forces the current through the SCR to zero.
 An LC circuit is connected across the SCR. A separate SCR or transistor is used to trigger
the LC circuit into resonance.
Operation:
 When a DC supply is applied to the circuit, the capacitor charges up to Vdc, with an upper
plate positive and lower plate negative. When the SCR is triggered, the current flows in
two directions: one is through Vdc+ – SCR – R – Vdc– and the another one is the
commutating current (IC) through L and C components.
 When the SCR is turned ON, the capacitor starts discharging in the path C+ – L – SCR –
C–. When the capacitor is fully discharged, it starts charging with a reverse polarity. As a
result of the reverse voltage, a commutating current IC, will flow in the opposite direction
of the load current IL.
 When the commutating current IC becomes higher than the load current, the SCR will
automatically turn OFF.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
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 The resonant frequency of the LC circuit is given by:
1
LC
 
where L is the inductance and C is the capacitance.
 The current in the LC circuit can be described by: ( ) ( )
LC m
I t I sin t


where Im is the peak current.
 The total current through the SCR is: ( )
total load LC
I I I t
 
 The condition for turning off the SCR is: total H
I I

Comparison between Natural Commutation and Forced Commutation
Feature Natural Commutation Forced Commutation
Basic Principle Utilizes the natural zero-crossing
of AC current to turn off the
SCR.
Uses external circuits to force the current
through the SCR to zero.
Application Commonly used in AC circuits. Used in DC circuits or AC circuits where
natural commutation is not possible.
Turn-off Trigger Current naturally falls to zero at
the end of each half cycle of the
AC supply.
An external circuit actively reduces the
current to zero.
Complexity Simple, relies on the inherent
properties of AC power.
More complex, requires additional
components and circuitry.
Components
Required
Typically does not require
additional components.
Requires components like capacitors,
inductors, and sometimes additional SCRs
or transistors.
Examples Line commutation in AC circuits,
such as in rectifiers.
Class A (Load Commutation) and Class B
(Resonant Pulse Commutation) in DC
choppers and inverters.
Reliability High, due to simplicity and fewer
components.
Potentially less reliable due to the
complexity and number of components
involved.
Efficiency High, with minimal energy loss. Efficiency can vary; losses may occur due
to additional components and switching
operations.
Ease of
Implementation
Easy in AC circuits; not
applicable for DC.
More challenging due to the design of
commutation circuits.
Examples of Use
Cases
AC power control, AC motor
drives.
DC motor drives, inverter circuits,
chopper circuits.
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SCR Gate Trigger Circuit/ SCR Firing Circuits
 SCRs require a gate trigger pulse to turn on and conduct current.
 Gate triggering circuits are designed to provide this pulse, which is typically a short
duration pulse of sufficient magnitude to exceed the gate trigger voltage VGT.
 The two common types of gate triggering circuits are:
1. Resistance Firing Circuit
2. Resistance-Capacitance (RC) Firing Circuit
1. Resistance Firing Circuit
 In a Resistance Firing Circuit, the gate of the SCR is triggered by a direct current through
a resistor connected between the gate and the cathode. This resistor limits the gate current
and controls the rise time of the gate voltage.
 The key components include a DC voltage, resistors (R1, R2&R3), and the SCR with its
anode, cathode, and gate terminals.
Operation:
 When the positive voltage is applied to the anode with respect to the cathode, the SCR
remains in non-conducting state until a gate current IG is applied.
 Gate Current Controlled by adjusting R2 to ensure IG exceeds the minimum gate current
IGT required for SCR turn-on.
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Gate Current (IG):
1
1
in D GT
G
V V V
I
R
 

where:
Vin: Input voltage
VD1: Voltage drop across diode D1
VGT: Gate trigger voltage of the SCR
R1: Resistance value of resistor R1
 Once IG>IGT, SCR conducts and allows current to flow through the load.
 The SCR turns off when the anode current falls below the holding current IH or when the
applied voltage drops below the holding voltage.
 Triggering Angle: Typically limited to 90 degrees in AC circuits due to maximum voltage
availability during the positive half-cycle.
2. Resistance-Capacitance (RC) Firing Circuit
 An RC Firing Circuit improves on the basic Resistance Firing Circuit by adding a capacitor
C in parallel with the gate resistor R. This combination allows for controlled charging and
discharging of the gate capacitance
 The limitation of resistance firing circuit can be overcome by the RC triggering circuit
which provides the firing angle control from 0 to 180 degrees.
 By changing the phase and amplitude of the gate current, a large variation of firing angle
is obtained using this circuit.
ELS: 2.4.1 POWER ELECTRONICS UNIT – I
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
P a g e | 71
Operation:
Positive Half-Cycle:
 During this period, the SCR becomes forward biased as the anode voltage rises.
 The capacitor C charges through the variable resistor R until its voltage reaches the gate
trigger voltage VGT.
( ) ( )
1 RCt
t
in
C
V t V e
 
 The current flowing through the resistor RRR and charging the capacitor C during the
positive half-cycle can be given by:
1
1
c
in D
V V V
I
R
 

 Diode D1 prevents reverse voltage across the SCR gate-cathode during the negative half-
cycle.
Negative Half-Cycle:
 Diode 2 allows the capacitor C to charge positively through R during the positive half-
cycle.
 It prevents reverse voltage across the SCR gate-cathode during the negative half-cycle.
 The capacitor holds the charge until the voltage across the capacitor is equal to the gate
trigger voltage.
Turn-On Condition: SCR turns on when the capacitor voltage VC reaches the gate trigger
voltage VGT.
********************

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ELS: 2.4.1 POWER ELECTRONICS Course objectives: This course will enable students to learn: Thyristors, power MOSFETs, power transistors, IGBT, MCT, LTT, smart power devices. Thyristor circuits: Converters, Inverters and motors operation and design.

  • 1. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 1 ELS: 2.4.1 POWER ELECTRONICS Introduction  Electrical power is the rate at which electrical energy is transferred by an electric circuit. W P = t where:  P is the power,  W is the work done or energy transferred,  t is the time over which the work is done or energy is transferred.  It quantifies the amount of energy consumed or produced by electrical devices and systems over time.  The fundamental definition of electrical power (P) is given by the product of voltage (V) and current (I) P = V×I where:  P is the electrical power measured in watts (W),  V is the voltage measured in volts (V),  I is the current measured in amperes (A).  The SI unit of electrical power is the watt (W), defined as one joule per second (J/s).  Electrical power can be expressed in several forms depending on the variables involved.  By substituting Ohm's Law into the basic power equation P = V×I, we get the other forms:  Substituting V=I⋅R into P=V⋅I: 2 P = I×R × ) I = I ( ×R  Substituting V I R  into IP=V⋅I: 2 R V ( ) R V P = V× =
  • 2. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 2 Power Electronics  Definition: Power Electronics is a specialized branch of electronics that deals with the study and application of electronic devices and circuits for the efficient control, conversion, and management of electrical power.  This field encompasses the design, implementation, and application of devices and systems for efficient power conversion and management.  The field of power electronics can be well understood by dividing it into two subcategories; i. Power Engineering: The field of power engineering mainly deals with the generation, transmission, distribution, and utilization of electrical energy at higher efficiency. ii. Power Electronics Engineering: Basically, in power electronics, solid-state electronics, is used that performs the action of control and convert of the electric power.
  • 3. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 3 Comparison Between Electronics and Power Electronics Aspect Electronics Power Electronics Purpose Processing, transmitting, and storing information Conversion, control, and conditioning of electric power Voltage and Current Levels Typically low (mV to a few V, mA to a few A) Typically high (kV, A to kA) Power Handling Typically milliwatts to watts Watts to megawatts Primary Components Resistors, capacitors, inductors, diodes, transistors Power Diodes, Power Transister, thyristors(SCR), MOSFETs, IGBTs, transformers Applications Computers, communication devices, consumer electronics Power supplies, motor drives, renewable energy systems Switching Speed Generally high Moderate to high, but with higher power handling Heat Dissipation Heat dissipation is relatively low. Heat dissipation is a significant concern due to high power levels, requiring efficient cooling systems. Thermal Management Less critical, often passive cooling Crucial, requires heat sinks, cooling fans, or liquid cooling Efficiency Less focus on efficiency High efficiency is critical Design Focus Signal integrity, miniaturization, low power consumption Efficiency, thermal management, high power handling Frequency Range High frequency (kHz to GHz) Low to moderate frequency (Hz to kHz, sometimes MHz) Control Characteristics Logic levels, signal processing Switching losses, conduction losses, thermal stability Protection Requirements Basic (overvoltage, overcurrent) Advanced (overvoltage, overcurrent, thermal shutdown)
  • 4. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 4 Need of Power Electronics Power electronics is crucial for modern technology and industry due to its ability to efficiently convert, control, and manage electrical power. Here are the key reasons for the need for power electronics: 1. Energy Efficiency Power electronics helps in improving the efficiency of energy conversion and utilization. By minimizing energy losses during conversion processes, it contributes to significant energy savings and reduced operational costs. 2. Renewable Energy Integration With the increasing adoption of renewable energy sources like solar and wind power, power electronics plays a vital role in converting and managing the variable output of these sources to ensure a stable and reliable power supply. 3. Electric Vehicles (EVs) Power electronics is essential in electric vehicles for efficient battery management, motor control, and power conversion. It enables the development of EVs with longer ranges, faster charging times, and improved performance. 4. Industrial Automation In industrial settings, power electronics is used for precise control of machinery and processes. Variable frequency drives (VFDs) and other power electronic devices allow for the efficient control of motors, leading to improved productivity and energy savings. 5. Consumer Electronics Power electronics is integral to the operation of various consumer devices, from smartphones and laptops to household appliances. It ensures these devices operate efficiently and reliably by managing power supply and distribution.
  • 5. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 5 6. Power Quality and Reliability Power electronics improves the quality and reliability of power supplied to both industrial and consumer applications. It helps in mitigating issues like voltage sags, harmonics, and power interruptions, ensuring a consistent and stable power supply. 7. Miniaturization and Compact Design The advancements in power electronic components allow for the development of smaller, lighter, and more efficient power systems. This miniaturization is essential for portable electronic devices and modern electrical equipment. 8. Smart Grids and Energy Management Power electronics is a key technology in the development of smart grids, which use advanced communication and control techniques to optimize the distribution and consumption of electricity. It enables better energy management, load balancing, and integration of distributed energy resources. 9. Cost Reduction By improving efficiency and reducing energy losses, power electronics can lead to significant cost savings in energy generation, transmission, and consumption. This is particularly important in large-scale industrial applications and utility grids. 10. Environmental Impact Efficient power conversion and management reduce the overall energy consumption and carbon footprint. Power electronics supports the transition to cleaner energy sources and promotes sustainable energy practices. Therefore, the need for power electronics arises from its ability to enhance energy efficiency, integrate renewable energy, support the development of electric vehicles, improve industrial automation, ensure reliable power supply, and contribute to environmental sustainability.
  • 6. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 6 Importance of Power Electronics:  Efficiency: Power electronics enables highly efficient energy conversion, reducing energy losses.  Control: Provides precise control over the delivery and quality of power.  Miniaturization: Allows the development of compact and lightweight power systems.  Integration: Facilitates the integration of renewable energy sources into the power grid. Power electronics is a critical field that supports the development of advanced technologies and sustainable energy solutions, playing a vital role in modern electrical and electronic systems. Applications of Power Electronics Power electronics is a versatile technology that finds applications across a wide range of fields. Here are some key applications in various sectors: 1. Renewable Energy Systems  Solar Power: Converters and inverters are used to convert the DC output of solar panels into AC for grid integration or local use.  Wind Power: Power electronics control the variable output of wind turbines and convert it into a stable AC supply.  Energy Storage: Battery management systems (BMS) and power converters manage the charge and discharge cycles of energy storage systems. 2. Electric Vehicles (EVs)  Motor Drives: Inverters control the electric motors, providing efficient and smooth operation.  Battery Chargers: Power electronic converters manage the charging process, ensuring fast and safe charging of EV batteries.  Regenerative Braking: Converts kinetic energy back into electrical energy to recharge the battery during braking.
  • 7. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 7 3. Industrial Applications  Motor Drives: Variable frequency drives (VFDs) and servo drives control industrial motors, enhancing efficiency and precision.  Welding: Power electronics control the welding process, providing consistent and high- quality welds.  Power Supplies: Switch-mode power supplies (SMPS) and uninterruptible power supplies (UPS) provide reliable and efficient power to industrial equipment. 4. Consumer Electronics  Power Adapters and Chargers: Convert AC to the appropriate DC voltage for devices like smartphones, laptops, and tablets.  Home Appliances: Efficient motor control and power management in appliances like washing machines, refrigerators, and air conditioners.  Lighting: LED drivers and dimmers control the brightness and efficiency of LED lighting systems. 5. Power Grids and Utility Systems  Smart Grids: Power electronics enable the integration of distributed energy resources, enhance grid stability, and optimize energy distribution.  HVDC Transmission: High-voltage direct current (HVDC) systems use power electronics for efficient long-distance power transmission.  FACTS Devices: Flexible AC Transmission Systems (FACTS) improve the reliability and capacity of power transmission networks. 6. Transportation  Rail Systems: Power converters and inverters control the traction motors of electric trains, improving efficiency and performance.  Aerospace: Power electronics manage the electrical systems of aircraft, ensuring reliable and efficient operation of avionics and other onboard systems.
  • 8. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 8 7. Healthcare  Medical Equipment: Power supplies and converters are crucial for imaging equipment (MRI, CT scanners), diagnostic devices, and patient monitoring systems.  Implantable Devices: Efficient power management in devices like pacemakers and insulin pumps. 8. Telecommunications  Power Supplies: Reliable power conversion and backup systems for telecommunication equipment and data centers.  Signal Processing: Power electronics are used in the amplifiers and transmitters of communication systems. 9. Military and Defense  Radar and Communication Systems: Power electronics ensure the efficient operation of radar, communication, and other defense systems.  Electric Propulsion: Used in naval and other defense vehicles for efficient propulsion and power management. 10. Environmental Control Systems  HVAC (Heating, Ventilation and Air Conditioning Systems) Systems: Variable speed drives and inverters control heating, ventilation, and air conditioning systems for better efficiency and comfort.  Energy Management Systems: Power electronics are integral to systems that monitor and optimize energy usage in buildings and industrial plants. Power electronics is a critical technology enabling advancements in energy efficiency, renewable energy integration, and the development of modern electronic and electrical systems across diverse fields.
  • 9. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 9 Power Semiconductor Devices  Power semiconductor devices have revolutionized the way we manage and control electrical power.  The journey began with early vacuum tubes and crystal detectors in the early 20th century.  A significant milestone was achieved in 1947 with the invention of the transistor at Bell Labs, accelerate the way for modern electronics.
  • 10. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 10 I. Vacuum Tubes  Early 20th Century: Vacuum tubes, also known as thermionic valves, were the first active electronic components used for amplification, switching, and rectification. They were made of glass enclosures containing electrodes in a vacuum.  Applications: Initially used in radio, television, and early computers.  Limitations: Vacuum tubes were bulky, consumed a lot of power, generated significant heat, and had limited reliability. II. Power Diodes  1940s: The invention of the semiconductor diode marked the beginning of solid-state electronics. The first semiconductor diodes were made from germanium.  1950s: Silicon diodes replaced germanium diodes due to their superior thermal stability and electrical characteristics.  Materials: Early diodes used germanium; modern power diodes use silicon.  Applications: Power rectification in power supplies, battery chargers, and various electronic circuits.
  • 11. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 11 III. Thyristors  1957: The silicon-controlled rectifier (SCR), a type of thyristor, was introduced by General Electric.  1960s: Other types of thyristors were developed, including TRIACs and DIACs.  Materials: Thyristors are primarily made from silicon.  Applications: AC/DC motor control, light dimmers, pressure control systems, and power switching. IV. Power Transistors  1950s: Bipolar Junction Transistors (BJTs) were developed from germanium and later silicon.  1960s: The development of the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) began to revolutionize power electronics.  1970s: The introduction of Insulated-Gate Bipolar Transistors (IGBTs) combined the best characteristics of BJTs and MOSFETs.  Materials: o BJTs: Initially germanium, later silicon. o MOSFETs: Silicon, and more recently, silicon carbide (SiC) and gallium nitride (GaN) for high-performance applications. o IGBTs: Primarily silicon, with emerging use of SiC for higher efficiency and thermal performance.  Applications: Switch-mode power supplies, motor drives, electric vehicles, renewable energy systems, and various industrial applications. Materials Used in Power Semiconductor Devices  Germanium (Ge): Early semiconductor devices, limited by lower thermal conductivity.  Silicon (Si): The dominant material for most power semiconductor devices due to its excellent electrical properties, thermal stability, and cost-effectiveness.  Silicon Carbide (SiC): Used in modern high-performance power devices for its superior efficiency, high voltage, and high-temperature operation.
  • 12. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 12  Gallium Nitride (GaN): Emerging material for high-frequency and high-efficiency applications, such as RF amplifiers and advanced power converters. Classification of Power Semiconductor Devices Power semiconductor devices can be broadly classified into two main categories: uncontrolled (two-terminal) and controlled (three-terminal) devices. 1. Uncontrolled Power Semiconductor Devices (Two-terminal) Uncontrolled devices are characterized by having only two terminals and cannot be actively controlled to switch them on or off. These devices conduct whenever a forward voltage is applied across their terminals. Examples:  Power Diodes: o Conduct when forward biased and block current when reverse biased.
  • 13. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 13 o Used primarily for rectification in power supplies, battery chargers, and various electronic circuits. 2. Controlled Power Semiconductor Devices (Three-terminal) Controlled devices have an additional terminal, known as the gate or control terminal, which allows them to be actively controlled to switch them on or off. This enables precise control over the flow of current through the device. Examples:  Thyristors: o Silicon-Controlled Rectifier (SCR):  Conducts when a gate signal is applied and continues to conduct until the current drops below a certain threshold.  Commonly used in AC/DC motor control, light dimmers, and power switching applications.  Transistors: o Bipolar Junction Transistors (BJTs):  Control current flow through the device by varying the base current.  Widely used in amplification and switching applications. o Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs):  Control current flow through the device by varying the gate-source voltage.  Commonly used in power electronics, such as in switch-mode power supplies and motor drives. o Insulated-Gate Bipolar Transistors (IGBTs):  Combine the high-current capability of BJTs with the voltage control of MOSFETs.  Used in high-power applications like motor drives, renewable energy systems, and traction applications.
  • 14. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 14 Control Characteristics of Power Devices The control characteristics of power devices refer to their behavior and response to control signals, which enable precise control and manipulation of electrical power in power electronic systems. 1. Switching Speed: This refers to how quickly a power device can transition between its ON and OFF states. Faster switching speeds are desirable in many applications as they minimize switching losses and improve efficiency. However, excessively fast switching can lead to issues like electromagnetic interference (EMI) and increased voltage stresses. sw on off t = t +t where tsw is the total switching time, ton is the turn-on time, and toff is the turn-off time. 2. Turn-On and Turn-Off Times: Turn-on time is the duration required for a power device to switch from the OFF state to the ON state, while turn-off time is the time taken to switch from the ON state to the OFF state. Minimizing these times helps in reducing switching losses and improving overall performance.  Turn-On Time (ton): on d r t = t +t where td is the delay time and tr is the rise time.  Turn-Off Time (toff): off f s t = t + t where tf is the fall time and ts is the storage time. 3. Conduction Losses: Power devices exhibit conduction losses when they are in the ON state. These losses are primarily due to the finite resistance of the device when conducting current. Lower conduction losses result in higher efficiency.
  • 15. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 15 2 conduction on P = I ×R where I is the current through the device and Ron is the on-state resistance of the device. 4. Switching Losses: Switching losses occur during the transition between the ON and OFF states. They consist of both turn-on and turn-off losses and are caused by the energy required to charge and discharge the device's capacitance and the time taken to complete these transitions. switching DS D on off sw 1 P = V ×I t +t )×f ( 2 where VDS is the drain-source voltage, ID is the drain current, ton is the turn-on time, toff is the turn-off time, and fsw is the switching frequency. 5. Reverse Recovery Time: In semiconductor devices such as diodes and thyristors, reverse recovery time refers to the time taken for the device to switch from the conducting state to the blocking state when the polarity of the applied voltage is reversed. Minimizing reverse recovery time reduces switching losses.
  • 16. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 16 rr p d t = t +t where:  tp is the storage time, during which the charge carriers recombine and the current remains constant or decreases slowly, after the forward current has been turned off.  Td is the fall time, during which the reverse recovery current decreases rapidly to zero. 6. Gate or Base Drive Requirements: Power devices such as MOSFETs, IGBTs, and BJTs require specific voltage and current levels at their gates or bases to switch them between ON and OFF states effectively. Understanding these requirements is crucial for proper device control and reliable operation. 7. Temperature Dependence: The performance of power devices often varies with temperature. Parameters such as threshold voltage, ON-state resistance, and leakage current can change significantly with temperature variations. Proper thermal management is essential to ensure reliable operation under different temperature conditions.
  • 17. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 17 8. Protection Features: Many modern power devices incorporate built-in protection features such as overcurrent protection, overvoltage protection, and thermal shutdown to safeguard against abnormal operating conditions and ensure device longevity. Block Diagram of Power Electronics The processing or converting of electric power is achieved through a power electronics converter also known as power converters or switching converters. 1. Source of Electrical Power:  The origin of the electrical energy supplied to the system. This can be an AC or DC source such as a battery, solar panel, or AC grid.  Provides the necessary power for the operation of the entire system. 2. Power Electronic Converter Circuit:  The core component that converts electrical power from one form to another. This can be inverters, rectifiers, DC-DC converters, or AC-AC converters.  Changes the voltage, current, or frequency according to the needs of the load or application. It also ensures efficient power conversion with minimal losses. 3. Electrical Load:  The device or component that consumes the electrical power. This can be anything from a motor, a lamp, a computer, or an entire industrial system.  The end-user of the electrical power which performs the desired function or operation.
  • 18. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 18 4. Sensor or Sensing Unit or Feedback Circuit:  Devices that monitor the performance and operational parameters of the power electronics system, such as current, voltage, temperature, or speed.  Provides real-time data and feedback to the control unit to ensure the system operates within desired parameters and to implement protection mechanisms. 5. Control Unit or Controller:  The brain of the power electronics system, which processes the feedback signals from the sensors and sends control signals to the converter circuit.  Regulates the operation of the power electronic converter to maintain the desired output, implement protection schemes, and optimize performance. This arrangement ensures that the power electronics system operates efficiently, safely, and meets the required performance criteria. Design of Power Electronics Equipment The design of power electronics equipment can be divided into steps to ensure that electrical energy is processed and controlled efficiently, meeting the specific requirements of the load.
  • 19. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 19 1. Design of Power Circuits: The design of power circuits involves creating the electrical pathways and selecting the components (e.g., SCR, MOSFETs, IGBTs) that will handle the main power flow within the system. 2. Protection of Power Devices: Protecting power devices from electrical, thermal, and environmental stresses to ensure reliable and safe operation. (e.g., fuses, circuit breakers, or current sensing circuits) 3. Determination of the control strategy: Designing algorithms such as PWM (Pulse Width Modulation), Implementing feedback loops that use sensor data to adjust the control signals and maintain system stability and performance. Deciding whether to use digital controllers (microcontrollers, DSPs, FPGAs) or analog controllers based on application needs. 4. Design of logic and gating circuits: Designing circuits that provide the necessary voltage and current levels to switch the power devices on and off efficiently. (e.g., Isolation, Timing and Synchronization) Microcontroller based Power Controller
  • 20. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 20 Comparison of DC Vs. AC, Single-Phase Vs. Three-Phase AC Parameter DC (Direct Current) AC (Alternating Current) Single Phase AC Three Phase AC Flow Direction One direction Reverses periodically Alternates periodically Alternates periodically Voltage Source Constant Varies sinusoidally Sinusoidal waveform Three sinusoidal waveforms, 120° apart Power Distribution Suitable for low- voltage applications Efficient for long- distance transmission Residential, small commercial Industrial, commercial, large motors Voltage Regulation Easier More complex Moderate Moderate to complex Typical Frequency 0 Hz 50 or 60 Hz 50 or 60 Hz 50 or 60 Hz Phase Angle N/A 0° 0° 120° between phases Applications Electronics, battery-powered devices Power distribution, electric motors Lighting, small appliances Industrial power distribution, motors
  • 21. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 21 Types of Power Electronic Circuits/Convertors Power electronic circuits are mainly classified into main four types I)AC to DC Converters (Rectifiers) AC to DC converters, or rectifiers, convert alternating current (AC) to fixed or variable direct current (DC). i)Diode Rectifiers(Uncontrolled): Convert AC voltage to a fixed DC voltage. ii)Phase(Controlled) Rectifiers: Convert AC voltage to a variable DC voltage. II) DC to DC Converters (Choppers) DC to DC converters, or choppers, convert a fixed DC input voltage to a variable DC output voltage.
  • 22. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 22 i) Step-down Chopper (Buck Converter): A step-down chopper, also known as a buck converter, reduces the input DC voltage to a lower output DC voltage. ii) Step-up Chopper (Boost Converter): A step-up chopper, also known as a boost converter, increases the input DC voltage to a higher output DC voltage. III) DC to AC Converters (Inverters) DC to AC converters, or inverters, convert fixed DC voltage to variable AC voltage and Frequency. i)Voltage Source Inverters (VSI): The input is a fixed DC voltage source. o Single-Phase VSI: Used in UPS systems and small-scale renewable energy systems. o Three-Phase VSI: Employed in industrial motor drives and grid-tied renewable energy systems. ii)Current Source Inverters (CSI): The input is a fixed DC current source. o Single-Phase CSI: Less common, used in specific industrial applications. o Three-Phase CSI: Used in large motor drives and industrial applications. IV)AC to AC Converters AC to AC converters change AC power from one form to another. i)Cycloconverters: Convert AC supply of fixed voltage and frequency to AC output of variable voltage and frequency. o Single-Phase to Single-Phase Cycloconverters o Three-Phase to Single-Phase Cycloconverters
  • 23. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 23 o Three-Phase to Three-Phase Cycloconverters Applications: Used in slow-speed large AC traction drives, rotary kilns, and multi-megawatt AC motor drives. ii)AC Voltage Controllers (AC Voltage Regulators): Change AC voltage while maintaining the same frequency. o Single-Phase AC Voltage Controllers: Common in lighting control and small motor speed control. o Three-Phase AC Voltage Controllers: Used in electronic tap changers and speed control of large fans and pumps. Comparison of Power Electronic Circuits/Converters Converter Type Sub-Type Function Applications I)AC to DC Converters (Rectifiers) i)Diode Rectifiers (Uncontrolled) Convert AC voltage to a fixed DC voltage Battery charging, power supplies, welding, UPS systems, electric traction, electroplating ii)Phase-Controlled Rectifiers Convert AC voltage to a variable DC voltage DC drives, HVDC systems, excitation systems, metallurgical, chemical industries, compensators II)DC to DC Converters (Choppers) i)Step-down Chopper (Buck Converter) Reduce input DC voltage to a lower output DC voltage Voltage regulation, battery charging, low-voltage DC motor drives ii)Step-up Chopper (Boost Converter) Increase input DC voltage to a higher output DC voltage Power factor correction, electric vehicles, renewable energy systems
  • 24. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 24 III)DC to AC Converters (Inverters) i)Voltage Source Inverters (VSI) Convert fixed DC voltage to variable AC voltage and frequency UPS systems, small-scale renewable energy systems, industrial motor drives, grid- tied renewable energy systems ii)Current Source Inverters (CSI) Convert fixed DC current to variable AC voltage and frequency Large motor drives, industrial applications IV)AC to AC Converters i)Cycloconverters Convert fixed AC voltage and frequency to variable AC voltage and frequency Slow-speed large AC traction drives, rotary kilns, multi- megawatt AC motor drives ii)AC Voltage Controllers (AC Voltage Regulators) Change AC voltage while maintaining the same frequency Lighting control, small motor speed control, electronic tap changers, speed control of large fans and pumps Power Transistors  Power transistors are three-terminal semiconductor devices designed to handle high currents and voltages.  Power transistors are fully controlled devices. This means they can be turned ON and OFF by applying an appropriate control signal.  They are categorized into three main types: I)Power Bipolar Junction Transistors (BJTs) II)Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), and III)Power Insulated-gate bipolar transistors (IGBTs).  Each type has its unique characteristics and applications. I)Power BJTs  Power BJTs, also known as bipolar junction transistors (BJTs), are three-terminal semiconductor current controlled devices that use both electrons and electron holes as charge carriers.
  • 25. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 25  A Power BJTs are designed to handle high current and voltage levels, making it suitable for power applications.  Presently power BJTs are available with ratings up to 1200 V, 800 A, with a maximum switching frequency of 10 kHz.  Because of higher mobility of electrons when compared with holes, n-p-n devices can be fabricated on a smaller silicon area to provide the same performance as an equivalent p-n- p device. So, the usage of n-p-n type of power BJT is more common in power electronics than p-n-p type.  Power BJTs can act as switches, amplifiers, or oscillators, depending on the biasing conditions Construction of Power BJT:  It consists of alternating P and N-type layers, with a drift region added to enhance its power handling capabilities. This region is characterized by a low doping level of approximately 10^14 cm^-3 and is responsible for the transistor's ability to handle high currents and voltages  The thickness of the dirft region determines the breakdown voltage of the Power transistor.  The characteristics of the device is determined by the doping level in each of the layers and the thickness of the layers.  The three terminals are the emitter (E), base (B), and collector (C).  Emitter (E): Highly doped with a high concentration of charge carriers, , typically 0.1-10μm.  Base (B): Lightly doped with a low concentration of charge carriers, typically 5-20 μm.
  • 26. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 26  Collector (C): Moderately doped with a concentration of charge carriers between that of the emitter and base, typically 50-200 μm.  The structure of a Power BJT is different from a signal-level transistor, with a four-layer structure of alternating P and N-type doping  The key differences in construction are:  Heavily doped n+ and p+ regions are used to carry large currents with minimal voltage drop  A lightly doped drift region is added between the collector and base to support high voltages in the off-state Steady State Characteristics of Power BJT Based on the forward and reverse bias condition of the power transistor, it operates in four regions.: Cut off region, Active region, Quasi saturation region, Hard saturation region
  • 27. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 27 1)Cut off region (OFF Switch)  In this region, both the base-emitter junction and the base-collector junction are reverse- biased.  The region below the characteristic for IB=0 is cut-off region. In this region, BJT offers large resistance to the flow of current. Hence it is equivalent to an open circuit.  In the cut-off region, the BJT is essentially off. There is no significant current flowing from collector to emitter.  Base current (IB): IB=0  Collector current (IC): IC≈0 (leakage current)  Collector-Emitter voltage (VCE ): VCE≈VCC 2)Active region/Liner Zone(Amplifier)  In the active region, the BJT operates as an amplifier. The base-emitter junction is forward- biased, and the base-collector junction is reverse-biased.  If BJT uses as an amplifier, it operates in this region. The dynamic resistance in this region is large. The power dissipation is maximum.  Collector current (IC): C B I I   , where β is the current gain of the transistor.  Collector-Emitter voltage (VC): ( ) CE CE sat V V  3)Quasi saturation region (Partially Saturation)  Quasi-saturation region is between the hard saturation and active region. This region exists due to the lightly doped drift layer.  In the quasi-saturation region, the transistor is partially saturated. This region occurs before full saturation, and the base-collector junction is not fully forward-biased.  When the BJT operates at high frequency, it is operated in this region. Both junctions are forward bias. The device offers low resistance compared to the active region.  So, power loss is less. In this region, the device does not go into deep saturation. So, it can turn off quickly. Therefore, we can use for higher frequency applications.  Collector-Emitter voltage (VCE): ( ) CE sat V VCE V    Base current (IB): Sufficiently high to keep the transistor out of the hard saturation region.
  • 28. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 28 4)Hard saturation region (Deep Saturation)  The Power BJT push into the hard-saturation region from the quasi-saturation region by increasing the base current. This region is also known as deep saturation region.  The resistance offers in this region is minimum. It is even less than the quasi-saturation region. So, when the BJT operates in this region, power dissipation is minimum.  The device acts as a closed switch when it operates in this region. But it needs more time to turn off. So, this region is suitable only for low-frequency switching application.  In this region, both junctions are forward bias. The collector current is not proportional to the base current, IC remains almost constant at IC(sat) and independent from the value of base current. Primary and Secondary Breakdown in Power BJT Primary Breakdown:  Primary breakdown occurs due to excessive voltage across the collector-emitter junction, leading to avalanche breakdown.  This occurs when the collector-emitter voltage (VCE) exceeds the maximum rated voltage (VCEO) of the transistor.  Avalanche Breakdown Condition: CE CEO V V 
  • 29. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 29  The breakdown voltage mechanism involves the transistor gain and the breakdown phenomenon in the PN junction. Secondary Breakdown:  Secondary breakdown occurs due to a combination of high voltage and high current, resulting in localized heating and thermal runaway.  It is characterized by the collapse of the collector-emitter voltage under high power dissipation conditions.  Secondary Breakdown Condition: ( ) CE C max V I PD   The Safe Operating Area (SOA) of the BJT is typically defined to prevent these breakdowns, ensuring that the device operates within safe limits of voltage, current, and power dissipation. II)Power MOSFETs  Power MOSFETs are enhancement mode voltage controlled majority carrier devices having three terminals namely, source (S), gate (G), and drain (D) used for low power high frequency switching applications (a few kW and 100s of kHz).  As a majority-carrier device, the MOSFET operates at much higher speed than BJT because there is no charge-storage mechanism. MOSFETs need continuous application of gate-to-source voltage to remain in the conducting state. MOSFETs do not suffer from second breakdown as BJTs do.
  • 30. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 30  Under steady-state conditions the gate draws very small current of the order of nano- amperes.  But, during turn-ON and turn-OFF it could be higher because of charging and discharging of the gate capacitance.  MOSFETs have very short switching times. Their ON-state resistance Rosin„) has positive temperature coefficient. So parallel operation of MOSFETs is simpler when compared to the parallel operation of BJTs.  Power are widely used in power electronics due to their high efficiency, fast switching speeds, and ease of drive. Enhancement Mode MOSFETs  Enhancement mode MOSFETs require a gate-to-source voltage (VGS) to be applied in order to turn on and conduct current between the drain and source.  In other words, the MOSFET is normally off when VGS is zero and only turns on when VGS exceeds a certain threshold voltage (Vth). Characteristics of Enhancement Mode MOSFETs  Normally Off: With no voltage applied to the gate, the device remains off, and there is no conduction path between the drain and source.  Threshold Voltage (Vth): The minimum gate-to-source voltage required to form a conductive channel between the drain and source.
  • 31. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 31  Positive VGS (for n-channel) or Negative VGS (for p-channel): A positive VGS for an n-channel MOSFET or a negative VGS for a p-channel MOSFET is needed to turn the device on. Depletion Mode vs. Enhancement Mode MOSFETs  Default State: Depletion mode MOSFETs are normally on (=0), while enhancement mode MOSFETs are normally off (=0).  Leakage Current: Depletion mode MOSFETs have higher leakage currents in the off state, whereas enhancement mode MOSFETs have lower leakage currents in the off state.
  • 32. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 32 Comparison Depletion Mode between Enhancement Mode MOSFETs Feature Depletion Mode MOSFET Enhancement Mode MOSFET Default State Normally On VGS=0 Normally Off VGS=0 Threshold Voltage (Vth) Negative (n-channel Positive (n-channel) Gate Control Negative VGS to turn off (n- channel) Positive VGS to turn on (n- channel) Applications Used in analog switches, depletion load devices Widely used in digital and power applications Control Less common, harder to control precisely More common, easier to control precisely Switching Speed Generally slower Generally faster Leakage Current Higher in off state Lower in off state Why Power MOSFETs are Typically Enhancement Mode?  Fail-Safe Operation: Enhancement mode MOSFETs are normally off, providing a safer default state in the absence of a control signal.  Efficiency: They have lower leakage currents when off, improving overall efficiency.  Control and Drive Simplicity: Require a single polarity drive voltage for operation, simplifying the gate drive circuitry.  Thermal Management: Easier to manage heat dissipation due to precise control over the on-state resistance (RDS(on)).  Design and Fabrication: More straightforward to design and fabricate for high-power and high-frequency applications.
  • 33. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 33 Construction of Power MOSFET  Power MOSFETs are built using a p-type substrate with heavily doped n+ source and drain regions. Over the channel region, a thin insulating layer of SiO2 is formed, and an aluminum layer serves as the gate.  To enhance the voltage rating, a lightly doped n- drift layer is included. This drift layer, along with the vertically oriented structure of alternating p and n layers, minimizes the current flow area, reducing on-state resistance and losses. The p-type middle layer, called the "body," and the n- "drift region" collectively determine the MOSFET's breakdown voltage.  The different types of power MOSFET have different attributes and therefore can be particularly suited for given applications.
  • 34. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 34 Type Structure Advantages Applications 1. Planar MOSFET Basic form High voltage ratings, dominated by epi-layer resistance High voltage applications 2. VMOS V-groove structure Lower ON resistance, better switching characteristics Power switching, small RF power amplifiers 3. UMOS Flattened groove Lower ON resistance, improved packing density, higher current density, better efficiency and reliability compared to VMOS Power switching 4. HEXFET Hexagonal structure Increased current capability Power applications 5. TrenchMOS Trench structure Better handling capacity and characteristics, lower ON resistance for voltages above 200 volts High voltage applications Device Operation of Power MOSFET Power MOSFET is a minority carrier device. So, conduction takes place only by the electrons. Therefore, the conduction cannot take place through the MOSFET from the drain to source due to the presence of P-layer in between. But this is possible by Inversion layer creation. Operation Phases: 1. Formation of the Depletion Region:
  • 35. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 35  The MOSFET is forward biased by connecting a positive voltage to its drain terminal with respect to source terminal and the gate is made positive with respect to the body layer.  The "P" layer of consists of a large number of holes and few electrons. The holes are majority carriers. Hence they outnumber the electrons which are minority carriers, still the number of electrons present in the "P" layer is sufficiently large.  Due to the positive voltage applied between gate body these electrons are attracted towards the gate and gather below the SiO2 layer and produce depletion layer by combining with the holes that are present there. Creation of the Inversion Layer (Induced Channel):  If the positive gate voltage is increased further, the number of electrons below the SiO2 layer will be greater than the number of holes.  Thus the conductivity of the part of P layer close to SiO2 layer will change from positive to negative. That means an n type of sub layer is formed below the SiO2 layer.
  • 36. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 36 • This process is known as creation of the inversion layer, and the process of generation of an inversion layer due to the externally applied gate voltage is known as the "field effect”. • The inversion layer is also called as the induced channel. This induced channel will connect the two n+ layers on either sides of the p-region. • In this way now the n type channel gets created in the P type body layer and conduction can take place through this layer. • The resistance of the induced channel is dependent on the magnitude of gate to base (body) voltage. Higher the gate voltage less is the resistance. The MOSFET acts as a variable resistor. • With increase in the gate to body voltage, the resistance will decrease. However, this resistance cannot decrease below a certain minimum value even with increase in the gate to body voltage. • If the maximum specified value of gate voltage is exceeded, then the SiO2 layer will breakdown. MOSFET Characteristics (Transfer, Output and Switching Characteristics) An n-channel Enhancement-type MOSFET allows current to flow from the drain to the source by applying a voltage to the gate.
  • 37. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 37 a) Transfer Characteristics  The transfer characteristics show the relationship between the drain current (IDS) and the gate-to-source voltage (VGS) for a constant drain-to-source voltage (VDS).  Below Threshold Voltage (VGS < VT): No current flows (IDS = 0) because the channel is not formed.  Above Threshold Voltage (VGS > VT): Current (IDS) increases as VGS increases. This region shows how the MOSFET turns on and how the gate voltage controls the drain current. b) Output Characteristics  The output characteristics show the relationship between the drain current (IDS) and the drain-to-source voltage (VDS) for various gate-to-source voltages (VGS).  Cut-off Region (VGS < VT): No current flows (IDS = 0) regardless of VDS.  Ohmic Region (Linear Region): For VGS > VT and low VDS, IDS increases linearly with VDS, and the MOSFET behaves like a variable resistor.  Saturation Region: At higher VDS, IDS levels off and becomes almost constant, determined by VGS. This region is also called the active region. c)Switching Characteristics  The switching characteristics of an n-channel Enhancement-type MOSFET describe how quickly and efficiently the MOSFET can turn on and off.  The turn-on & turn-off times of the MOSFET get affected by its internal capacitance and the internal impedance of the gate drive circuit. But these internal capacitances have no effect during steady state operation.  These characteristics are crucial for applications in switching power supplies, digital circuits, and other high-speed switching applications.
  • 38. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 38 Switching Process 1. Turn-On Process: o Initial State: The MOSFET is off with no current (=0) flowing between the drain and source. o Gate Voltage Applied: When a positive gate-to-source voltage (VGS) is applied, the gate-to-source capacitance (Cgs) starts to charge. o Turn-on Delay (td(on)): This is the time taken for the gate voltage to reach the threshold voltage (VT) and start forming the channel. ( ) ( ) ( ) 1 g gs t R C G GS t V V e   
  • 39. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 39 o Rise Time (tr): Once VGS exceeds VT, the channel forms quickly, and IDS rises to its maximum value. 2 ( ) 2 T GS DS V V I K   o The total turn-on time (ton) is the sum of the turn-on delay and the rise time: on r d( = t on) t +t 2. Turn-Off Process: o Initial State: The MOSFET is on with current (IDS) flowing between the drain and source. o Gate Voltage Removed: When the gate voltage is removed, the gate-to-source capacitance (Cgs) starts to discharge. o Turn-off Delay (td(off)): This is the time taken for VGS to fall below the threshold voltage (VT). During this period, the channel starts to collapse. ( ) ( ) g gs t R C G GS t V V e   o Fall Time (tf): Once VGS drops below VT, the channel collapses quickly, and IDS falls to zero. ( ) 0 ( ) t RgCgs DS D I t I e   , where ID0 is the initial current. o The total turn-off time (toff) is the sum of the turn-off delay and the fall time: f ( t = t off + t Of ) f d Factors Affecting Switching Characteristics  Gate Capacitance: Higher capacitance results in slower switching times due to longer charging and discharging periods.  Gate Resistance: Higher resistance increases the time constants for charging and discharging the gate capacitance, slowing down the switching speed.
  • 40. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 40  Driver Strength: Stronger gate drivers can provide higher current to charge and discharge the gate capacitance faster, improving switching speed.  Parasitic Inductances: Inductances in the circuit can cause delays and ringing during switching transitions, affecting the overall performance. III) Power IGBTs  IGBT is a three terminal device having a collector (C), emitter (E), and the gate (G). The collector and emitter are the power terminals. Gate and emitter are the control terminals. An IGBT has the merits of both BJT and MOSFET.  They combine the high input impedance and fast switching of MOSFETs with the high- voltage and high-current capabilities of bipolar junction transistors (BJTs). i.e., IGBTs are composite devices that combine the input characteristics of a MOSFET with the output characteristics of a BJT.  IGBT does not have any second breakdown problem like a BJT.  An IGBT can also be designed to block negative voltages. This is not possible in the case of BJTs and MOSFETs.  IGBTs have come closer to the 'ideal switch', with typical voltage ratings of 600 - 1700 volts, ON-state voltage of 1.7 - 2.0 volts at currents of up to 1000 amperes, and switching speeds of 200 - 500 ns.  The availability of IGBTs has lowered the cost of systems and enhanced the number of economically practical applications.
  • 41. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 41 Construction of IGBT Similar to MOSFET, the vertically oriented structure of an IGBT is designed to maximize the area available for current flow, reducing the resistance and on-state power loss. P+ Injection Layer (Drain Layer): This layer forms the drain of the IGBT and is responsible for injecting holes into the N- drift region, enhancing conductivity and current flow. N+ Buffer Layer: This layer serves two important purposes:  Reducing On-State Voltage Drop: The N+ buffer layer helps to reduce the voltage drop across the device when it is in the on-state, improving its efficiency.  Shortening Turn-Off Time: The N+ buffer layer also helps to shorten the turn-off time of the IGBT, enhancing its switching performance. N- Drift Region: This layer is designed to improve the breakdown voltage capacity of the IGBT. It is similar to the structure used in power MOSFETs. P-Type Base/Gate: The P-type base is heavily doped to reduce resistance and improve the switching performance of the IGBT. N-Type Collector and Emitter: The N-type collector and emitter are also heavily doped to enhance the current-carrying capacity of the IGBT. Gate-Source Structure: The IGBT uses a highly interdigitated gate-source structure to reduce the possibility of source/emitter current crowding, ensuring more efficient current flow.
  • 42. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 42 Device Operation of IGBT The principle of operation of IGBT is similar to that of a MOSFET. The operation can be divided into two parts: i)Creation of Inversion Layer  Similar to MOSFETs, the operation of an IGBT begins with the application of a positive voltage between the gate and the source (VGS).  When VGS exceeds the threshold voltage (Vth), an inversion layer is formed beneath the oxide layer, inducing an N-type channel in the P-type body region. This allows the flow of current from the collector to the emitter. ii) Conductivity Modulation
  • 43. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 43 Conductivity Modulation:  Unlike MOSFETs, IGBTs exhibit conductivity modulation, a process that reduces on-state losses. During the device's ON state, carriers (electrons) are injected from the emitter into the N- drift layer, reducing its resistance.  This injection of carriers increases the conductivity of the drift region, effectively lowering the on-state voltage drop across the device. Double Injection Mechanism:  The conductivity modulation process involves a phenomenon known as "double injection."  Electrons are injected from the heavily doped N+ emitter region (J1) into the N- drift layer (J3) when junction J3 is forward biased.  Simultaneously, holes are injected from the P+ layer into the N+ buffer layer (J2), creating a double injection of carriers into the N- drift region.  This double injection of electrons and holes enhances the conductivity of the N- drift region, effectively reducing its resistance and improving the overall performance of the IGBT. Output and Transfer Characteristics of IGBT
  • 44. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 44 i)Transfer Characteristics  The transfer characteristics of an IGBT describe the relationship between the gate-emitter voltage (VGE) and the collector current (IC) while keeping the collector-emitter voltage (VCE) constant.  when VGE is below the threshold voltage (VGET), the device remains in the off state, and IC is practically zero.  As VGE exceeds VGET, the IGBT enters the active region, and IC starts to increase. ii) Output Characteristics The transfer characteristics of IGBT illustrate the relationship between input voltage, VGE, and output collector current, IC.  When VGE is 0V, the device remains off with no IC, and when VGE slightly increases but stays below VGET, it remains off but may exhibit a leakage current.  Once VGE surpasses the threshold, IC begins to rise, turning the device on. As a unidirectional device, current flows in only one direction.  The relationship between collector current, IC, and collector-emitter voltage, VCE, at different VGE levels.
  • 45. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 45  At VGE < VGET the GBT is in cutoff mode, resulting in IC = 0 at any VCE. Beyond VGE > VGET, the IGBT enters the active mode, where IC increases with rising VCE. Comparison of Power (BJTs), Power (MOSFETs) and IGBTs Characteristic Power BJT Power MOSFET IGBT Voltage Rating High < 1kV High < 1kV Very High > 1kV Current Rating High < 500 A Low < 200 A Very High > 500 A Frequency Medium High Medium to High Secondary Breakdown Yes No No Input Drive Circuitry Complex Simple Simples Input Impedance Low High High Output Impedance Low Medium Low Switching Loss High Low Medium Switching Speed Low Fast Medium Cost Low Medium High Power Applications General purpose, high power, audio amplification Low voltage, high frequency applications, DC-DC converters, motor drives Motor drives, inverters, UPS systems, renewable energy systems Thyristors  Thyristors are a type of semiconductor device that can be used to control the flow of electrical current, used for rectification and switching in high-power circuits.  The most common type of thyristor is the Silicon-Controlled Rectifier (SCR)  The word Thyristor is formed from two words thyratron and transistor.  Besides, the characteristics possessed by a thyristor is the combination of the properties of thyratron and transistor.
  • 46. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 46  The thyratron has the property of rectification and the transistor has the property of switching.  The thyristors are turned on using the control signal transferred by the transistor. Unlike the diodes, the thyristors have three terminals Anode, Cathode and Gate terminal.  SCRs typically handle voltages from a few volts up to 10kv and currents from a few milliamperes up to 1.5kA which respond to 15MW power handling capacity.  Thyristors are widely used in applications such as motor control, light dimmers, and pressure control systems.
  • 47. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 47 Construction of SCR  It consists of four layers of alternating p-type and n-type materials, forming a PNPN.  The SCR has four layers of extrinsic semiconductor materials, which form three PN junctions named J1, J2, and J3. The SCR has three junctions: J1: Between the p-type outer layer and the n-type outer layer. J2: Between the p-type inner layer and the n-type inner layer. J3: Between the p-type inner layer and the n-type outer layer.  The anode and cathode terminals are placed at the end layers, and the gate terminal is placed with the third layer. The outer layers are heavily doped, and the inner two layers are lightly doped.
  • 48. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 48 Principle of Operation of SCR  The operation of SCR is divided into two categories, i) When Gate is open and ii) When Gate is closed. i)When gate is open:  Consider that the anode is positive with respect to cathode and gate is open. • The junctions Ji and 13 are forward biased and junction J2 is reverse biased.  There is depletion region around J2 and only leakage current flows which is negligibly small.  Practically the SCR is said to be OFF. This is called forward blocking state of SCR and voltage applied to anode and cathode with anode positive is called forward voltage. Forward Blocking State Reverse Blocking State  With gate open, if cathode is made positive with respect to anode, the junctions J1, J3 become reverse biased and J2 forward biased. Still the current flowing is leakage current, which can be neglected as it is very small.  The voltage applied to make cathode positive is called reverse voltage and SCR is said to be in reverse blocking state.
  • 49. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 49  In forward blocking state, if the forward voltage is increased and made sufficiently large, the reverse biased junction J2 breaks down and SCR conducts heavily. This voltage is called forward break over voltage VB0 of SCR. In such condition, SCR is said to be ON or triggered. ii)When gate is closed:  Consider that the voltage is applied between gate and cathode when the SCR is in forward blocking state.  The gate is made positive with respect to the cathode.  The electrons from n-type cathode which are majority in number, cross the junction .13 to reach to positive of battery.  While holes from p type move towards the negative of battery, this constitutes the gate current.  This current increases the anode current as some of the electrons cross junction 12. As anode current increases, more electrons cross the junction J2 and the anode current further increases.  Due to regenerative action, within short time, the junction J2 breaks and SCR conducts heavily. The resistance R is required to limit the current.  Once the SCR conducts, the gate loses its control.
  • 50. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 50 Static Anode- Cathode Characteristics of SCR  The static anode-cathode characteristics of an SCR (Silicon-Controlled Rectifier) describe the relationship between the anode current (IA) and the anode-cathode voltage (VAK) under different conditions.  The static characteristic is divided into three modes: 1. Forward Blocking mode 2. Forward conduction mode 3. Reverse Blocking mode Static V-I Characteristics
  • 51. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 51 1. Forward Blocking mode:  VAK>0 (positive voltage applied to the anode relative to the cathode), Gate is not triggered.  When anode is at a higher potential than cathode, thyristor is said to be forward biased, It is seen from the figure that when the gate circuit is open J1 and J3 are forward biased and junction J2 is reverse bias.  In this mode a small current, called forward leakage current flows from anode to cathode.  OM represents the forward blocking mode of SCR  SCR is treated as an open switch in the forward blocking mode. 2. Forward Conduction mode:  VAK>0 (positive voltage applied to the anode relative to the cathode), Gate is triggered.  When anode to cathode forward voltage is increased with gate circuit open, reverse biased junction J2 will have an avalanche breakdown at a voltage called forward break over voltage VBO.  After this breakdown, thyristor gets turned ON with point 'M' at once shifting to 'N'. Here NK represents the forward conduction mode.
  • 52. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 52  A thyristor can be brought from forward blocking mode to forward conducting mode by applying.  A positive gate pulse between gate and cathode or  A forward breakover voltage VBO across anode and cathode.  Voltage drop across the SCR 'VT' increases slightly with an increase in anode current. It can be seen from NK. Latching Current:  It is defined as the minimum value of anode current which it must attain during turn-on process to maintain conduction when gate signal is removed.  The gate pulse width should be chosen to ensure that the anode current rises above the latching current. Holding Current:  It is defined as the minimum value of anode current below which the SCR gets turned off.  Latching current is more than Holding current.  Latching current is associated with turn on process.  Holding current is associated with turn off process.
  • 53. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 53 3. Reverse Blocking mode:  VAK<0 (negative voltage applied to the anode relative to the cathode).  When cathode is made high potential with respect to anode with gate open, then the SCR is said to be reverse biased.  J1 and J3 are reverse biased and J2 is forward biased.  A small current flows through the SCR this is called as reverse leakage current.  This is reverse blocking mode, called the OFF state of the SCR.  If the reverse voltage increased, then at reverse breakdown voltage VBR, an avalanche breakdown occurs at J1 and J3 and the reverse current increases rapidly PQ.  The SCR in the reverse blocking mode may therefore be treated as an open switch. Two transistor model of SCR  The two transistor model of SCR is a simplified representation of the device's operation, which combines the p and n layers into two interconnected transistors: one PNP and one NPN.  This model helps to explain the SCR's behavior and is useful for analyzing its operation.  The two-transistor model of an SCR (Silicon-Controlled Rectifier) consists of an NPN transistor (T2) and a PNP transistor (T1) connected back-to-back.
  • 54. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 54 Structure:  T1 (PNP): Base connected to T2's collector.  T2 (NPN): Base connected to T1's collector.  G: Gate terminal.  A: Anode terminal.  K: Cathode terminal. Operation:  When switch S is closed, a positive pulse is applied to the base of T2 (NPN).  T2 (NPN) starts conducting, creating a short circuit between its collector and emitter, bringing the negative terminal voltage to the base of T1 (PNP).  This negative voltage causes T1 (PNP) to conduct as well.  Both transistors T1 and T2 conduct, forming a short-circuited path and allowing current to flow from the supply voltage V through the load resistor R.
  • 55. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 55 Mathematical Analysis of the two-transistor model According to the transistor leakage current equation, the collector current is given as Therefore, for the first transistor T1, we can say, As for the first transistor, the emitter current equals to the anode current Ia.For the second transistor, T2 As the emitter current in the case of the second transistor is equal to the cathode current of the second transistor Ik. By applying KCL in the circuit, we can say,
  • 56. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 56 Again, by applying KCL, we can say Therefore, Ia can be given as Hence,  If in equation (α1 + α2) =1, -IA =∞  SCR suddenly latches to the ON state from OFF state condition, this characteristic of device is called regenerative action.  Once the SCR goes into conduction, the two transistor model is no more applicable. Here note that the internal regeneration takes place in the SCR due to avalanche breakdown of reverse biased junction J2.  It does not take place when SCR is reverse biased. When the current through the SCR falls below holding current, the forward blocking state is regained. Then α1 and α2 of transistors are also reduced to small values. Gate Characteristics of SCR The gate characteristics of an SCR (Silicon-Controlled Rectifier) refer to the relationship between the gate current (IG) and the gate-cathode voltage (VGK), as well as how these parameters influence the SCR's operation.
  • 57. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 57
  • 58. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 58
  • 59. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 59 Turn-ON Methods and Turn-OFF Methods of SCR The turn-on and turn-off mechanisms of thyristors, particularly silicon-controlled rectifiers (SCRs), are crucial for their proper operation in various electronic circuits. This response will cover the different methods of turning on and off SCRs. I) Turn-ON Methods for SCRs (SCR Triggering)  Turning on an SCR involves initiating conduction between the anode and cathode, allowing current to flow through the device. The SCR remains in the off state (blocking state) until it is properly gate triggered.  The SCR can be made to conduct or switched from blocking (non-conducting or OFF) state to Conduction (ON) State by any one of the following methods. The main methods to turn on an SCR are: 1. Forward Voltage Triggering 2. Gate Triggering 3. dv/dt Triggering 4. Thermal Triggering 5. Light Triggering
  • 60. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 60 1. Forward Voltage Triggering  In forward voltage triggering, the SCR is turned on by applying a voltage across the anode and cathode that exceeds the breakover voltage (VBO). This method utilizes the intrinsic properties of the SCR's junctions.  When the applied voltage (VAK) exceeds the breakover voltage, the depletion region at the junction breaks down, causing a large current to flow through the SCR.  The condition for forward voltage triggering is: AK BO V V  where VAK is the anode-to-cathode voltage and VBO is the breakover voltage.  Once VBO, the SCR enters into the conduction state and remains on as long as the current through it is above the holding current (IH). 2. Gate Triggering  Gate triggering is the most common and practical method to turn on an SCR. It involves applying a small positive current to the gate terminal with respect to the cathode while the anode is positive.
  • 61. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 61  A gate current (IG) injects charge carriers into the base region of the SCR, initiating the conduction process.  The SCR turns on if the gate current IG is above a certain threshold : G GT I I   The anode current (IA) increases as the gate current IG is applied, reducing the forward blocking voltage and allowing the SCR to turn on. 3. dv/dt Triggering  This method relies on a rapid rate of rise of the anode-to-cathode voltage (dv/dt) to turn on the SCR.  In this type of triggering, whenever the SCR is in forwarding bias, then two junctions like J1 & J3 are in forwarding bias and J2 junction will be in reverse bias. Here, J2 junction performs like a capacitor because of the existing charge across the junction. If the ‘V’ is the voltage across the SCR, then the charge (Q) and capacitance can be written as
  • 62. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 62 0 ( ) When C C I dQ dt Q CV d CV dV dC dt dt d I c v d C t dt          The induced current due to dv/dt is given by: AK C dV I C dt  where C is the junction capacitance and AK dV dt is the rate of change of the anode-to-cathode voltage.  Thus, as the change of voltage rate across the SCR turns into high or low, then the SCR may trigger.  If this induced current exceeds the latching current of the SCR, it will turn on. 4. Thermal Triggering  Thermal triggering involves increasing the junction temperature to reduce the breakover voltage.  Increasing temperature reduces the bandgap energy, thereby reducing the breakover voltage and allowing the SCR to turn on at a lower applied voltage. 0 0 ( ) ( ) ( ) BO BO V T V T T T     where VBO(T) is the breakover voltage at temperature VBO(T0) is the breakover voltage at a reference temperature T0, and α is the temperature coefficient.  As the temperature increases, VBO decreases, leading to forward voltage triggering at a lower applied voltage.  However, in certain circumstances, an SCR can be unintentionally triggered by an external voltage transient or rapid voltage rise (dv/dt).  Unintentional dv/dt triggering can be a problem in SCR applications because it may lead to unexpected or premature triggering, causing the SCR to conduct when it shouldn't, leading to potential issues like false triggering or damage to the device.
  • 63. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 63 5. Light Triggering  When the SCR is triggered with the radiation of light is named as LASCR or Light Activated SCR. This kind of triggering is used for converters which are controlled by phase within HVDC systems. In this technique, intensity and light emissions with suitable wavelength are permitted to hit the J2 junction.  Light triggering uses photon energy to generate electron-hole pairs in the junction of the SCR.  When the SCR is exposed to light, photons impart energy to the electrons, creating electron-hole pairs. These charge carriers reduce the barrier potential, initiating conduction.  The number of generated electron-hole pairs depends on the intensity of the incident light and can be approximated by: L L I P    where IL is the photocurrent, η is the quantum efficiency, and PL is the incident light power.  If the photocurrent ILI_LIL is sufficient to exceed the latching current, the SCR will turn on.
  • 64. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 64 II)Turn-OFF Methods for SCRs  Turning off an SCR involves stopping the current flow through the device, bringing it back to the off state.  The SCR naturally stays on as long as the current through it remains above a certain threshold called the holding current.  The methods to turn off an SCR are primarily focused on reducing this current below the holding current. Commutation:  Commutation of SCRs refers to the process of turning off the SCR.  Commutator switches are essential for the operation of DC machines, providing reliable and straightforward methods for current reversal and rectification. The main turn-off methods are: i) Natural Commutation (Line Commutation) ii) Forced Commutation i) Natural Commutation (Line Commutation)  Natural commutation, also known as line commutation, takes advantage of the natural zero-crossing of the AC supply voltage. This method is inherently used in AC circuits where the current naturally passes through zero during each half cycle.
  • 65. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 65  In an AC circuit, the current through the SCR will naturally drop to zero at the end of each half cycle. When the current through the SCR falls below the holding current (IH), the SCR turns off.  The condition for natural commutation is: A H I I  where IA is the anode current and IH is the holding current.  During each zero-crossing of the AC waveform, the anode current reduces to zero, thus turning off the SCR. ii) Forced Commutation  Forced commutation is used in DC circuits or in AC circuits where natural commutation is not possible.  It involves externally forcing the current through the SCR to zero using additional circuitry.  Forced Commutation is classified into different types. They are: Class A –Commutation Class B –Commutation Class C – Complementary Commutation Class D – Auxiliary Commutation Class E – Pulse Commutation
  • 66. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 66 a) Class A Commutation (Load Commutation)  Class A commutation uses an LC circuit in parallel with the load to force the current through the SCR to zero.  The SCR is connected in series with the load, and an LC resonant circuit is placed in parallel with the load. Operation:  When the SCR is conducting, the load current flows through it.  The LC circuit is charged during this period.  Once the LC circuit is fully charged, it starts discharging, creating a reverse current that opposes the load current.  This reverse current forces the total current through the SCR to drop below the holding current, thus turning it off.  The resonant frequency of the LC circuit is given by: 1 LC   where L is the inductance and C is the capacitance.  The current in the LC circuit can be described by: ( ) ( ) LC m I t I sin t   where Im is the peak current.  The condition for turning off the SCR is: total load LC H I I I I   
  • 67. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 67 b) Class B Commutation (Resonant Pulse Commutation)  Class B commutation employs a resonant LC circuit connected across the SCR to create an oscillatory current that forces the current through the SCR to zero.  An LC circuit is connected across the SCR. A separate SCR or transistor is used to trigger the LC circuit into resonance. Operation:  When a DC supply is applied to the circuit, the capacitor charges up to Vdc, with an upper plate positive and lower plate negative. When the SCR is triggered, the current flows in two directions: one is through Vdc+ – SCR – R – Vdc– and the another one is the commutating current (IC) through L and C components.  When the SCR is turned ON, the capacitor starts discharging in the path C+ – L – SCR – C–. When the capacitor is fully discharged, it starts charging with a reverse polarity. As a result of the reverse voltage, a commutating current IC, will flow in the opposite direction of the load current IL.  When the commutating current IC becomes higher than the load current, the SCR will automatically turn OFF.
  • 68. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 68  The resonant frequency of the LC circuit is given by: 1 LC   where L is the inductance and C is the capacitance.  The current in the LC circuit can be described by: ( ) ( ) LC m I t I sin t   where Im is the peak current.  The total current through the SCR is: ( ) total load LC I I I t    The condition for turning off the SCR is: total H I I  Comparison between Natural Commutation and Forced Commutation Feature Natural Commutation Forced Commutation Basic Principle Utilizes the natural zero-crossing of AC current to turn off the SCR. Uses external circuits to force the current through the SCR to zero. Application Commonly used in AC circuits. Used in DC circuits or AC circuits where natural commutation is not possible. Turn-off Trigger Current naturally falls to zero at the end of each half cycle of the AC supply. An external circuit actively reduces the current to zero. Complexity Simple, relies on the inherent properties of AC power. More complex, requires additional components and circuitry. Components Required Typically does not require additional components. Requires components like capacitors, inductors, and sometimes additional SCRs or transistors. Examples Line commutation in AC circuits, such as in rectifiers. Class A (Load Commutation) and Class B (Resonant Pulse Commutation) in DC choppers and inverters. Reliability High, due to simplicity and fewer components. Potentially less reliable due to the complexity and number of components involved. Efficiency High, with minimal energy loss. Efficiency can vary; losses may occur due to additional components and switching operations. Ease of Implementation Easy in AC circuits; not applicable for DC. More challenging due to the design of commutation circuits. Examples of Use Cases AC power control, AC motor drives. DC motor drives, inverter circuits, chopper circuits.
  • 69. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 69 SCR Gate Trigger Circuit/ SCR Firing Circuits  SCRs require a gate trigger pulse to turn on and conduct current.  Gate triggering circuits are designed to provide this pulse, which is typically a short duration pulse of sufficient magnitude to exceed the gate trigger voltage VGT.  The two common types of gate triggering circuits are: 1. Resistance Firing Circuit 2. Resistance-Capacitance (RC) Firing Circuit 1. Resistance Firing Circuit  In a Resistance Firing Circuit, the gate of the SCR is triggered by a direct current through a resistor connected between the gate and the cathode. This resistor limits the gate current and controls the rise time of the gate voltage.  The key components include a DC voltage, resistors (R1, R2&R3), and the SCR with its anode, cathode, and gate terminals. Operation:  When the positive voltage is applied to the anode with respect to the cathode, the SCR remains in non-conducting state until a gate current IG is applied.  Gate Current Controlled by adjusting R2 to ensure IG exceeds the minimum gate current IGT required for SCR turn-on.
  • 70. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 70 Gate Current (IG): 1 1 in D GT G V V V I R    where: Vin: Input voltage VD1: Voltage drop across diode D1 VGT: Gate trigger voltage of the SCR R1: Resistance value of resistor R1  Once IG>IGT, SCR conducts and allows current to flow through the load.  The SCR turns off when the anode current falls below the holding current IH or when the applied voltage drops below the holding voltage.  Triggering Angle: Typically limited to 90 degrees in AC circuits due to maximum voltage availability during the positive half-cycle. 2. Resistance-Capacitance (RC) Firing Circuit  An RC Firing Circuit improves on the basic Resistance Firing Circuit by adding a capacitor C in parallel with the gate resistor R. This combination allows for controlled charging and discharging of the gate capacitance  The limitation of resistance firing circuit can be overcome by the RC triggering circuit which provides the firing angle control from 0 to 180 degrees.  By changing the phase and amplitude of the gate current, a large variation of firing angle is obtained using this circuit.
  • 71. ELS: 2.4.1 POWER ELECTRONICS UNIT – I Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24 P a g e | 71 Operation: Positive Half-Cycle:  During this period, the SCR becomes forward biased as the anode voltage rises.  The capacitor C charges through the variable resistor R until its voltage reaches the gate trigger voltage VGT. ( ) ( ) 1 RCt t in C V t V e    The current flowing through the resistor RRR and charging the capacitor C during the positive half-cycle can be given by: 1 1 c in D V V V I R     Diode D1 prevents reverse voltage across the SCR gate-cathode during the negative half- cycle. Negative Half-Cycle:  Diode 2 allows the capacitor C to charge positively through R during the positive half- cycle.  It prevents reverse voltage across the SCR gate-cathode during the negative half-cycle.  The capacitor holds the charge until the voltage across the capacitor is equal to the gate trigger voltage. Turn-On Condition: SCR turns on when the capacitor voltage VC reaches the gate trigger voltage VGT. ********************