chapter_1 Intro. to electonic Devices.ppt

Department of Electrical Power Engineering
Faculty of Electrical & Electronic Engineering
1

Lesson Plan and Learning
Outcomes
 Student will know the definition and concepts of
power electronics.
 Students would identify the power semiconductor
switches.
 Students are able to compare the rating of the
switches.
 Student will know several applications of power
electronics devices.
 The snubbers cct, Power switch losses, and
gate/base drive cct.
2

CONTENTS
1.1 Introduction
1.2 Power Electronic Systems
1.3 Electronic Converters
1.3.1. Controlled Rectifier (AC to DC Converter)
1.3.2. Chopper (DC to DC Converter)
1.3.3. Inverter (DC to AC Converter)
1.3.4. Cycloconverter (AC to AC Converter)
1.3.5. AC Voltage Controller
1.4 Applications of Power Electronic Converters
1.5 Power Semiconductor Devices
1.5.1. Power Diode
1.5.2. Power Transistor
3

CONTENTS
1.6 Power MOSFET
1.7 Insulated Gate Bipolar Transistor (IGBT)
1.8 Thyristor (SCR)
1.8.1. Voltage-Ampere (V-I) Characteristics
1.8.2. Thyristor Conduction
1.9 GTO Thyristor (Gate-Turn-Off)
1.10 IGCTs (Integrated Gate Commutated Thyristor)
1.11 Switching Power Loss in Controllable Switches
1.12 Gate and Base Drive Circuits
1.13 Electrical Isolation for Drivers
4

1.1 Introduction
 What is Power Electronics?
 Power electronic deal with the use of electronic for
the control and conversion of large amounts of
electrical power.
 The designs of PEs equipment involves interaction
between:
-Electronic
-Power
-Control
5

Relationship of PE to Power, Electronic
& Control
6
CONTROL
Analog || Digital
ELECTRICAL POWER
(SOURCE):AC || DC
(LOAD):STATIC || ROTATING
ELECTRONIC
Devices || Circuit

8
Power Electronics Application
POWER ELECTRONIC
CONVERTER

10
PE Applications
Commercial Applications
• HVAC system
• UPS
• Lift/Elevators
• Emergency lamps
• Welding systems
Domestic Applications
• Cooking equipments.
• Lighting & heating
ckts.
• Air conditioners.
• Refrigerators.
• P C.
• Battery Chargers

 Telecommunications
 Battery chargers.
 DC power supply &
UPS
 Mobile cell phone
battery chargers.
11
Transportation
• Traction control of
electric vehicles.
• Electric locomotives.
• Electric Boat
• Street cars & trolley
buses.
PE Applications

 Utility Systems
 High voltage DC transmissions (HVDC).
 Static VAR compensation.
 Solar sells/Fuel cells converter.
 Energy storage systems.
 Harmonic Filter.
12
PE Applications

13
PE Applications
1. Static Application
 involves non-rotating or moving mechanical
components.
 Examples:
DC Power supply, un-interruptible power supply, power
generation and transmission (HVDC), electronic ballast and etc.
2. Drive application
 intimately contains moving or rotating
components such as motor.
 Examples:
Electric trains, electric vehicles, air-conditioning system,
pump, compressor and etc.

PE Growth
PE rapid growth due to:
Advances in power (semiconductor) switches.
Advances in microelectronics (DSP,
microprocessor/microcontroller).
New ideas in control algorithms.
Demand for new applications.
14

Digital/analogue electronics.
Power and energy.
Microelectronics.
Control systems.
Computer, simulation & software.
Packaging
Heat transfer
15
PE Interdisciplinary Field

20
-All in One ???
Radio, Music, TV, Video, dictionary,
eBooks, Games, PC
Freezer???
Perfumes???
Umbrella???, etc

Future PE Application ???
 Electrical Energy Wireless Transmission
Development
It is possible ???????
21

23
1.2 Power Electronic System
Basic Block Diagram of Power Electronics System
Power
Converter
Controller
Load
Reference
Power
Input
Sensor
Unit

1.3 Power Converters
 The Power Converter is designed to convert, i.e. to
process and control the flow of electric power by
supplying voltage and current in a form that is
optimally suited for user loads with high efficiency,
high reliability, low cost, small size and weight.
24

Classification of Power Converter
25
1. AC-DC Converter

28
4. AC-AC Converter
(Cycloconverter)

1.5 Power Semiconductor
Devices
Can be categorized into:
Uncontrolled – Diode
Semi-controlled – Thyristor (SCR)
Fully controlled – Power transistor; e.g: BJT,
MOSFET, IGBT, IGCT,GTO
The rating of the switches are stated in
terms of voltage rating, current rating,
frequency and ON-state voltage.
29

The Modeling of Semiconductor Devices
Ideal switches Model
- Switch closed (on): v(t)=0
- Switch open (off): i(t) =0
- Switch power :p(t) =v(t)i(t)
= 0
31
i(t)
v(t)

Basic limitations of semiconductor
devices
32
- The maximum voltage, it is according to
the breakdown value of the silicon p-n
junction Vmax
- The maximum current, it is according
to the current density of the electrode
Imax.
- Maximum Power Handling Capability
PHmax, product of the maximum
voltage and current.

33
I
V
Vmax
Imax
PHmax
SOA
Save Operating Area of the
semiconductor devices

Power Switches
 Power Diodes
- Stud type
- Hockey-puck type
- etc.
34

Power Switches
 IGBT
- Module type: Full bridge
and three phase.
- etc.
35
• IGCT
- Integrated with its
driver

Power Switches
 Thyristor or SCR (silicon
controlled rectifier)
- Switched on gate terminal, the
device remain latched.
36
Thyristor voltage regulated by phase
control
vo
ig

1.5.1 Power Diodes
37
• Structure: two layers P-N semiconductor device
• Voltage-current characteristic:
- Forward voltage : as a closed switch
- reverse voltage : as a open switch

38
• Forward biased – conducts current with small forward
voltage (Vf)
• Reversed (blocking state) – a small leakage current (μA –
mA) flows until the reverse breakdown occurs.
• Diode should not be operated at reverse voltage greater
than VPRV.
Id
Vd
Practical ideal

Power Diodes
 When the input voltage is greater than the diode
volt-drop the diode is in forward conduction.
 When the supply voltage falls below VD , the
conduction is blocked and the load is separated
from the source by the blocking diode
39

Power Diodes (Reverse
recovery)
 When the diode switched quickly from
forward to reverse bias, it continues to
conduct due to the minority carriers which
remains in the p-n junction.
41

42
-IA
IA
0
Time (µsec)
Fast
recovery
conventional
• The minority carriers requires finite time, trr
(reverse recovery time) to recombine with
opposite charge and neutralize.

recovery)
 Two types:
1) Snap-off
43
Softness factor,
Sr

recovery)
 Two types:
2) Soft-recovery
44
Softness factor,
Sr

recovery)
 If trr is high, the diode cannot be used in high
frequency application.
 Effects of reverse recovery:
- increase switching losses
- increase voltage rating
- over-voltage (spikes) in inductive loads.
45

General
Purpose Diodes
Fast Recovery
Diodes
Schottky
Diodes
Upto 6000V &
3500A
Upto 6000V and
1100A
Upto 100V and
300A
Reverse
recovery time –
High
Reverse
recovery time –
Low
Reverse
recovery time –
Extremely low.
46
Comparison between different
types of Diodes

Typical of Gate Driver Signal
51
Pulse Gate Signal:
- Controlled Turn-on: SCR,TRIAC
- Controlled Turn-on and turn-off:
GTO,IGCT

Typical of Gate Driver Signal
52
Continuous Gate Signal: IGBT,MOSFET,BJT

53
Typical of Gate Driver Source
Current Driven Gate:
- Threshold of the gate: current
- Examples: BJT, SCR, GTO and IGCT
Voltage Driven Gate:
- Threshold of the gate: voltage
- Examples: MOSFET and IGBT
*The voltage gate driver circuit is more
simpler than the current gate driver
circuit

54
1.8 Thyristor (SCR)
• Thyristor is a family name for bi-polar devices
which comprise four semi-conductor layers.

55
V-I characteristics
Thyristor (SCR)

56
• Can turn ON but hard to turn OFF.
• Requires large voltage before can ON.
• If the forward breakover voltage (Vbo) is
exceeded, the SCR self-triggers into
conducting state.
• If the gate current is occurs, it will reduce
Vbo.
• Condition to turn ON:
 Forward blocking state (Vak must be +).
 Ig (gate current) is applied.
• In reverse-biased – SCR behaves like a diode.
Thyristor (SCR)

57
Example SCR circuit, another

58
Thyristor (SCR)
Condition to turn OFF: anode current
become zero
i) Ia goes to negative (-ve portion of
supply current) – natural commutation.
ii) Using forced commutation.
• Cannot be turn OFF by applying
negative gate current.

59
Thyristor (SCR)
• Types of thyristor:
i) Phase controlled.
ii) Inverter grade.
iii) Light activated.
iv) Triac (Bidirectional Thyristor)
v) Diac (Diode AC)

Triac (Bidirectional Thyristor)
60

Diac (Diode Alternating
Current)
61

62
1.9 Gate Turn-Off Thyristor (GTO)
• GTO is a thyristor that can be triggered into
conduction by a small positive gate-current
pulse (like SCR), but also be turned off by a
negative gate-current pulse (unlike SCR).
• Turning off needs very large reverse gate
current (normally 1/5 of anode current).
• Ratings:
Voltage VAK < 5kV
Current IA < 5 kA
Switching freq up to 5 kHz

Gate Turn-Off Thyristor
(GTO)
63
Turn-off characteristics

65
1.5.2 Power Transistors
• Can be turn ON and OFF by relatively
very small control signals.
• Operated at saturation and cut-off
modes only.
• No linear region operation is allowed due
to excessive power loss.

66
Transistor characteristics
VCE
Active Sat
Cutoff
VBE
IB
Transfer function

67
Bipolar Junction Transistor (BJT)
• The transistor is a
current-driven device.
• The base current
determines whether it is
in the on state or the off
state.
• To keep the device in the
on state there must be
sufficient base current.
• Continuous Gate Control

F
B
C I
I 

F
C
B
I
I


68
βF = forward current gain >> 1
The colector-emiter leakage current neglected
F
C
C
E
I
I
I




69
• The high-voltage power switching
transistors is commonly in NPN rather
than PNP.
• Power transistors usually in Darlington
form.
Darlington
βF1
βF2
• BJT with βF1 = βF2=40
• IE1= …..?
• IE2= …..?

70
• Rating:
Voltage VCE < 1000V,
Current Ic < 400 A
Switching freq up to 5kHz
• Expensive and the base drive circuit is complex.
• Current driven devices

1.6 Metal Oxide Silicon Field Effect
Transistor (MOSFET)
 There are two types of MOSFETs:
depletion-type (normally on)
enhancement-type (normally off)
 Voltage drive device
71

Symbol and Characteristic
Depletion-MOSFET
73

Symbol and Characteristic
Enhance-MOSFET
74

Different P vs N-MOSFET
 P- MOSFET:
- The threshold voltage: Positif [ Vt>0]
 N- MOSFET:
- The threshold voltage: Negatif [ Vt<0]
76

Metal Oxide Silicon Field Effect
Transistor (MOSFET)
 Rating:
Voltage VDS < 500V
Current IDS < 300A
f > 100 kHz
 Superior – high switching with very nice waveform
(up to MHz).
 The gate drive cct (simple) – When have high f the
passive component (L & C) can be reduced.
 Biggest application is in switch-mode power supply.
77

Metal Oxide Silicon Field Effect
Transistor (MOSFET)
 Advantages:
- High input impedance due to insulated gate (thus no gate
current, no gate power)
- Fast switching (thus less switching losses, suitable for
frequencies above 100kHZ)
- Positive temperature coefficient, good for parallel
operation
 Disadvantages:
Higher conduction loss, lower voltage & current capability
78

1.7 Insulated Gate Bipolar Transistor
(IGBT)
 Hybrid semiconductor devices –
combination of BJT and MOSFET.
 The gate is voltage driven, as in the
MOSFET.
 Ratings:
Voltage VCE < 3.3kV
Current IC < 1.2 kA
Switching freq up to 100 kHz
 Voltage drive device
80

81
• Typical forward characteristics of
IGBT as a function of gate potential

83
Turn off with inductive load IGBT-Turn off Energy dissipation

1.10 Insulated Gate-Commutated
Thyristor (IGCT)
 Among the latest power switches (1996).
 Conduct as thyristor but can be turn off using gate
signal, similar to IGBT.
 Power switch is integrated with the gate drive unit.
 Ratings:
- voltage Vak < 6.5 kV
- current Ia < 4 kA
- Frequency < 1 kHz
 Very low an state voltage – 2.7 V
84

Comparison of Power Electronic Devices
86

Comparison of Power Electronic Devices
87

1.2 Gate and Base Drive Circuits
88
• Interface between control circuit (low power electronics)
and high power switch.

Gate and Base Drive Circuits
89
Functions:
• To switch a power semiconductor device from off state to the on
state and vice versa.
• The drive circuit amplifies the control signals to levels required
to drive the power switch.
• Provides electrical isolation and signal isolation between the
power switch terminal and logic level of control circuit.
• May included in drive circuit for protection of power switch from
over currents.

Two Main Components of Gate Driver
90
optocoupler use for signal isolation
Transformer use for electrical isolation

91
• The component values to be used and the
complexity of a drive circuit will vary depending
on the characteristics of the power switch being
driven.
• For example, the MOSFET or IGBT drivers are
simple but for GTO it is vary complicated and
expensive.

92
Simple MOSFET gate
driver
• The MOSFET requires VGS
= +15 V for turn on and 0 V
to turn off.
• When the output of the
comparator is low, VGS is
pulled to VGG.
• If VGG is set to +15 V, the
MOSFET turn on.
• When output of the
comparator is high, VGS is
pulled to the ground, then
the MOSFET is off.

93
Simple Thyristor gate
driver
• In this circuit, a pulse
transformer is used to
conduct the thyristor with
the R1 is to limit the gate
current.
• Normally, a pulse with
length of 10 us and
amplitude of 50 mA is
sufficient to turn-on the
thyristor.
• However, this simple circuit is not possible to turn-off the
thyristor.

1.3 Electrical Isolation for Drivers
94
• Very often, there is need for
electrical isolation between the
logic-level control signals and
the drive circuit to prevent
damages on the high power
switch to propagate back to low
power electronics.
• The basic ways to provide
electrical isolation are:
- optocoupler
- fiber optics
- transformer.
• Many standard driver chips have buit-in isolation for example TLP-20 from
Toshiba and HP 3150 from Hewlett-Packard uses optocoupling isolation.

Electrical Isolation for Drivers
95
Schematic of an optocoupler use for signal isolation in drive circuit

96
Protection of Power Switches -
Snubbers
• The voltage across the switch is bigger than the
supply (for a short moment) cause a spike.
• The spike may exceed the switch rated blocking
voltage and causes damage due to over-voltage.
• A snubber is put across the switch – RCD circuit.
• Snubber circuit “smoothened” the transition and
make the switch voltage rise more “slowly”.
• Reduce switching losses

97
Protection of Power Switches -
Snubbers
RCD circuit

98
Current waveform without and
using Snubbers

99
V,I&P without and using
Snubbers

1.11 Power Switch Losses
 The sources of losses generally include:
 Conduction loss: a function of the forward volt-drop &
conduction current (more significant at lower
frequency operation).
 Off-state leakage loss: associated with the leakage
current during blocking state.
 Switching loss: during the devices turning on and
turning off (can be significant at a relative high
frequency).
100

Power Switch Losses
102
The turn-on-crossover interval
The energy dissipation during on-state interval can be express as
The turn-off crossover interval tc(off),
fv
ri
on
c t
t
t 

)
( )
(
)
( 2
1
on
c
o
d
on
c t
I
V
W 
on
o
on
on t
I
V
W 
Energy dissipated during turn-on transition
Energy dissipated during turn-off transition
fi
rv
off
c t
t
t 

)
(
)
(
)
( 2
1
off
c
o
d
off
c t
I
V
W 

Power Switch Losses
103
Hence, the average switching power loss Ps during turn-on and
off transition can be approximated as
The average power dissipated during on-state in one cycle can
be written as
Therefore, the total average power dissipation is
)
(
2
1
)
(
)
( off
c
on
c
s
o
d
s t
t
f
I
V
P 

s
on
o
on
on
T
t
I
V
P 
on
s
T P
P
P 


Controlled Power Semiconductor
Components Characteristic
104
Components Symbol Gate Control Typical Gate driver
Signal
Typical Gate Driver
Source
Turn-on Turn-off Pulse Continuous Current Voltage
1 Diode
2 SCR √ √ √
3 IGBT √ √ √ √
4 MOSFET
5 TRIAC
6 GTO
7 BJT
8 IGCT

 Semiconductor power devices such as BJT, GTO and IGBT have power
dissipation during turn on and turn off. Therefore it is important to consider
this matter in designing a power electronic circuit. Figure Q1(b) has shown the
switching characteristic of a typical semiconductor power device. If it is given
that tcon=4ns,tcoff=6ns,ton=3us,toff=1us and operates at switching frequency
of 100kHz . If the total average power dissipation, PT is 1.75 watt, current flow
through the switch is 5 A and switch on-state voltage is 1 V. Calculate;
 (i) the average power dissipated during on-state, PON.
 (ii) the average switching power loss, PS.
 (iii) the input voltage (voltage across the switch during off-state), Vd.
 (iv) what is the new switching frequency if it is required to reduce the
average power dissipated PON as in Q1(b)(i) by 50%.
106

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