This document contains questions and answers related to power electronics devices and converters. It begins with definitions of key power electronics terms:
- IGBT is popular due to lower switching losses and smaller snubber circuit requirements.
- Thyristors can be turned on through forward voltage, gate, dv/dt, temperature, or light triggering.
- Power diodes have higher voltage, current, and power ratings than signal diodes due to a drift region construction.
- IGBTs, power MOSFETs, and power BJTs are voltage, voltage, and current controlled devices respectively due to how their output current is controlled by their input signals.
- There are N-channel and P-channel
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
The manual is useful for PG students belongs to ME power Electronics and Drives
By
M.MURUGANANDAM. M.E.,(Ph.D).,MIEEE.,MISTE,
Assistant Professor & Head / EIE,
Muthayammal Engineering College,
Rasipuram,
Namakkal-637 408.
Cell No: 9965768327
The manual is very useful for UG EEE students for the subject Power Electronics
By
M.MURUGANANDAM. M.E.,(Ph.D).,MIEEE.,MISTE,
Assistant Professor & Head / EIE,
Muthayammal Engineering College,
Rasipuram,
Namakkal-637 408.
Cell No: 9965768327
Chopper basically uses a Thyristor for high power applications. The process of turning off a conducting Thyristor is known as commutation. Here Thyristor is turned off by a current pulse that is why it is called a Current Commutated Chopper.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
The manual is useful for PG students belongs to ME power Electronics and Drives
By
M.MURUGANANDAM. M.E.,(Ph.D).,MIEEE.,MISTE,
Assistant Professor & Head / EIE,
Muthayammal Engineering College,
Rasipuram,
Namakkal-637 408.
Cell No: 9965768327
The manual is very useful for UG EEE students for the subject Power Electronics
By
M.MURUGANANDAM. M.E.,(Ph.D).,MIEEE.,MISTE,
Assistant Professor & Head / EIE,
Muthayammal Engineering College,
Rasipuram,
Namakkal-637 408.
Cell No: 9965768327
Chopper basically uses a Thyristor for high power applications. The process of turning off a conducting Thyristor is known as commutation. Here Thyristor is turned off by a current pulse that is why it is called a Current Commutated Chopper.
Dual converter is a power electronics control system to get either polarity DC from AC rectification by forward converter and reverse converter . It can run a DC motors in either direction with speed control too.
Dual converter is a power electronics control system to get either polarity DC from AC rectification by forward converter and reverse converter . It can run a DC motors in either direction with speed control too.
A hybrid converter topologies which can supply simultaneously AC as well as DC from a single DC source. The new Hybrid Converter is derived from the single switch controlled Boost converter by replacing the controlled switch with voltage source inverter (VSI). This new hybrid converter has the advantages like reduced number of switches as compared with conventional design having separate converter for supplying AC and DC loads, provide DC and AC outputs with an increased reliability, resulting from the inherent shoot through protection in the inverter stage. For controlling switches PWM control, based upon unipolar Sine-PWM is described.
SPEED CONTROL OF SEPARATELY EXCITED DC MOTOR USING POWER ELECTRONIC CONVERTER ijiert bestjournal
In a modern technology the use of power electronic devices in the control strategies of
electrical drives is increasing. The speed of a DC motor can be varied by controlling the field
flux, the armature resistance or the terminal voltage applied to the armature circuit. The three
most common speed control methods are field resistance control, armature voltage control,
and armature resistance control. But here a technique of drive has been used for DC motor’s
speed control is chopper and some power electronics devices. It has been shown here the use
of chopper and power electronics devices which paves the way of controlling also torque and
speed characteristics of DC motor. Now the simulation of model is done and analysed in
MATLAB (Simulink) under varying speed and torque condition
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
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Mechanical, Industrial and Manufacturing Engineering,
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Aerospace Engineering.
Hardware Analysis of Resonant Frequency Converter Using Isolated Circuits And...IJERD Editor
-LLC resonant frequency converter is basically a combo of series as well as parallel resonant ckt. For
LCC resonant converter it is associated with a disadvantage that, though it has two resonant frequencies, the
lower resonant frequency is in ZCS region[5]. For this application, we are not able to design the converter
working at this resonant frequency. LLC resonant converter existed for a very long time but because of
unknown characteristic of this converter it was used as a series resonant converter with basically a passive
(resistive) load. . Here, it was designed to operate in switching frequency higher than resonant frequency of the
series resonant tank of Lr and Cr converter acts very similar to Series Resonant Converter. The benefit of LLC
resonant converter is narrow switching frequency range with light load[6] . Basically, the control ckt plays a
very imp. role and hence 555 Timer used here provides a perfect square wave as the control ckt provides no
slew rate which makes the square wave really strong and impenetrable. The dead band circuit provides the
exclusive dead band in micro seconds so as to avoid the simultaneous firing of two pairs of IGBT’s where one
pair switches off and the other on for a slightest period of time. Hence, the isolator ckt here is associated with
each and every ckt used because it acts as a driver and an isolation to each of the IGBT is provided with one
exclusive transformer supply[3]. The IGBT’s are fired using the appropriate signal using the previous boards
and hence at last a high frequency rectifier ckt with a filtering capacitor is used to get an exact dc
waveform .The basic goal of this particular analysis is to observe the wave forms and characteristics of
converters with differently positioned passive elements in the form of tank circuits.
AC - AC power conversions were traditionally done by using thyristor power controllers, phase angle control or by
integral cycle control, but had low PF and other disadvantages. Variable voltage, variable frequency high power conversions
are nowadays use DC link and Matrix converters, with higher efficiency and better regulation. But in situations where only
voltage regulation is required and the circuit need to be simple and less complicated, directed PWM AC-AC converters are
more preferred, due to reduced size and components. This project presents the design and simulation of a new type of AC-AC
converter which can operate as traditional non-inverting buck and boost converters, and inverting buck-boost converter as
well. This converter uses six unidirectional current flowing and bidirectional voltage blocking switches, implemented by six
reverse blocking IGBTs or series MOSFET-diode pairs, two input and output filter capacitors, and one inductor. It has no
shoot-through problem of voltage source (or capacitor) even when all switches are turned-on and therefore; PWM dead times
are not needed resulting in high quality waveforms, and solves the commutation problem without using bulky and lossy RC
snubbers or dedicated soft-commutation strategies. It has smaller switching losses because; only two switches out of six are
switched at high frequency during each half cycle of input voltage, and it can use power MOSFETs as body diode never
conducts, making it immune from MOSFET failure risk..
International Journal of Engineering Research and Applications (IJERA) aims to cover the latest outstanding developments in the field of all Engineering Technologies & science.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
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SOLID STATE TRANSFORMER - USING FLYBACK CONVERTERAbhin Mohan
FUTURISTIC ELECTRICAL ENGINEERING PROJECT.
A Device that can step up as well as step down coltage and get output as both DC or AC. Total flexibility of Power using DC link by Flyback Coverter.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
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Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
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Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
Andreas Schleicher presents at the OECD webinar ‘Digital devices in schools: detrimental distraction or secret to success?’ on 27 May 2024. The presentation was based on findings from PISA 2022 results and the webinar helped launch the PISA in Focus ‘Managing screen time: How to protect and equip students against distraction’ https://www.oecd-ilibrary.org/education/managing-screen-time_7c225af4-en and the OECD Education Policy Perspective ‘Students, digital devices and success’ can be found here - https://oe.cd/il/5yV
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
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The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
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It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
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Bills have a main role in point of sale procedure. It will help to track sales, handling payments and giving receipts to customers. Bill splitting also has an important role in POS. For example, If some friends come together for dinner and if they want to divide the bill then it is possible by POS bill splitting. This slide will show how to split bills in odoo 17 POS.
This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
CLASS 11 CBSE B.St Project AIDS TO TRADE - INSURANCE
Ee6503(r 13) qb-2013_regulation
1. Fatima Michael college of Engineeringand Technology
DEPARTMENTOFELECTRICALANDELECTRONICSENGINEERING
Question bank
POWER ELECTRONICS
1. Why IGBT is very popular nowadays?
a. Lower hate requirements
b. Lower switching losses
c. Smaller snubbed circuit requirements
2. What are the different methods to turn on the thyristor?
a. Forward voltage triggering
b. Gate triggering
c. dv/dt triggering
d. Temperature triggering
e. Light triggering
3. What is the difference between power diode and signal diode?
Power diode Signal diode
1.Constructed with n-layer, called
drift region between p+ layer and
n+ layer.Drift region is not present.
2.The voltage, current and power
ratings are higher.Lower3.Power diodes operate at high speeds. Operates at higher
switching speed.
4. IGBT is a voltage controlled device. Why?
Because the controlling parameter is gate-emitter voltage.
5. Power MOSFET is a voltage controlled device. Why?
Because the output (drain) current can be controlled by gate-source voltage.
6. Power BJT is a current controlled device. Why?
Because the output (collector) current can be controlled by base current.
7. What are the different types of power MOSFET?
a. N-channel MOSFET
b. P-channel MOSFET
8. How can a thyristor turned off?
A thyristor can be turned off by making the current flowing through it to zero.
9. Define latching current.
3ndYEAR/ 5thSEMESTER
UNIT-I POWER SEMI-CONDUCTOR DEVICES
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2. The latching current 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.
10. Define holding current.
The holding current is defined as the minimum value of anode current below which
it must fall to for turning off the thyristor.
11. What is a snubber circuit?
It consists of a series combination of a resistor and a capacitor in parallel with the
thyristors. It is mainly used for dv / dt protection.
12. What losses occur in a thyristor during working conditions?
a. Forward conduction losses
b. Loss due to leakage current during forward and reverse blocking.
c. Switching losses at turn-on and turn-off.
d. Gate triggering loss.
13. Define hard-driving or over-driving.
When gate current is several times higher than the minimum gate current required, a
thyristor is said to be hard-fired or over-driven. Hard-firing of a thyristor reduces its turn-on
time and enhances its di/dt capability.
14. Define circuit turn off time.
It is defined as the time during which a reverse voltage is applied across the
thyristor during its commutation process.
15. Why circuit turn off time should be greater than the thyristor turn-off time?
Circuit turn off time should be greater than the thyristor turn-off time for reliable
turn-off, otherwise the device may turn-on at an undesired instant, a process called
commutation failure.
17. What is the turn-off time for converter grade SCRs and inverter grade SCRs?
Turn-off time for converter grade SCRs is 50 – 100 ms turn-off time for converter
grade SCRs and inverter grade SCRs and for inverter grade SCRs is 3 – 50 ms.
18. What are the advantages of GTO over SCR?
a. Elimination of commutation of commutating components in forced commutation,
resulting in reduction in cost, weight and volume.
b. Reduction in acoustic noise and electromagnetic noise due to elimination of
commutation chokes.
c. Faster turn-off, permitting high switching frequencies.
d. Improved efficiency of the converters.
3
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3. 19. What is meant by phase controlled rectifier?
It converts fixed ac voltage into variable dc voltage.
20. Mention some of the applications of controlled rectifier.
a. Steel rolling mills, printing press, textile mills and paper mills employing dc
motor drives.
b. DC traction
c. Electro chemical and electro-metallurgical process
d. Portable hand tool drives
e. Magnet power supplies
f. HVDC transmission system
PART- B
1. a) Discuss the different modes of operation of thyristor with the help of static
VI characteristics. (8)
1. b) Explain the construction of SCR with neat sketch. (8)
2. Draw the switching characteristics of SCR and explain it. (16)
3. Discuss the different modes of operation of TRIAC with the help of VI
characteristics. (16)
4. Explain the switching characteristics of TRIAC (16)
5. With the help of neat diagram explain the operation of BJT. (16)
UNIT-II
PHASE-CONTROLLED CONVERTERS
1. What is the function of freewheeling diodes in controlled rectifier?
It serves two process.
a. It prevents the output voltage from becoming negative.
b. The load current is transferred from the main thyristors to the freewheeling diode,
thereby allowing all of its thyristors to regain their blocking states.
2. What are the advantages of freewheeling diodes in a controlled in a controlled
rectifier?
a. Input power factor is improved.
b. Load current waveform is improved and thus the load performance is better.
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4. 3. What is meant by delay angle?
The delay angle is defined as the angle between the zero crossing of the input
voltage and the instant the thyristors is fired.
4. What are the advantages of single phase bridge converter over single phase mid-
point converter?
a. SCRs are subjected to a peak-inverse voltage of 2Vm in a fully controlled bridge
rectifier. Hence for same voltage and current ratings of SCrs, power handled by
mid-point configuration is about
b. In mid-point converter, each secondary winding should be able to supply the load
power. As such, the transformer rating in mid-point converter is double the load
rating.
5. What is commutation angle or overlap angle?
The commutation period when outgoing and incoming thyristors are conducting
isknown as overlap period. The angular period, when both devices share conduction is
known as the commutation angle or overlap angle.
6. What are the different methods of firing circuits for line commutated converter?
a. UJT firing circuit.
b. The cosine wave crossing pulse timing control.
c. Digital firing schemes.
7. Give an expression for average voltage of single phase semiconverters.
Average output voltage Vdc = (Vm / _) (1 + cos _ ).
8. What is meant by input power factor in controlled rectifier?
The input power factor is defined as the ratio of the total mean input power to
thetotal RMS input volt-amperes.
PF = ( V1 I1 cos _1 ) / ( Vrms Irms) where V1 = phase voltage, I1 =
fundamentalcomponent of the supply current, _1 = input displacement angle, Irms = supply
rms current.
9. What are the advantages of six pulse converter?
a. Commutation is made simple.
b. Distortion on the ac side is reduced due to the reduction in lower order
harmonics.
c. Inductance reduced in series is considerably reduced.
10. What is meant by commutation?
It is the process of changing the direction of current flow in a particular path of the
circuit. This process is used in thyristors for turning it off.
5
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5. 11. What are the types of commutation?
a. Natural commutation
b. Forced commutation
12. What is meant by natural commutation?
Here the current flowing through the thyristor goes through a natural zero and
enable the thyristor to turn off.
13. What is meant by forced commutation?
In this commutation, the current flowing through the thyristor is forced to become
zero by external circuitry.
14. What is meant by dc chopper?
A dc chopper is a high speed static switch used to obtain variable dc voltage from
a constant dc voltage.
15. What are the applications of dc chopper?
a. Battery operated vehicles
b. Traction motor control in electric traction
c. Trolly cars
d. Marine hoists
e. Mine haulers
f. Electric braking.
16. What are the applications of dc chopper?
Chopper provides
a. High efficiency
b. Smooth acceleration
c. Fast dynamic response
d. Regeneration
17. What is meant by step-up and step-down chopper?
In a step- down chopper or Buck converter, the average output voltage is less than
the input voltage. In a step- up chopper or Boost converter, the average output voltage is
more than the input voltage.
18. Write down the expression for average output voltage for step down chopper.
Average output voltage for step down chopper V0 = _ Vs, _ is the duty cycle
19. Write down the expression for average output voltage for step up chopper.
Average output voltage for step down chopper V0 = Vs, _ is the duty cycle
1-
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6. 20. What is meant by duty-cycle?
Duty cycle is defined as the ratio of the on time of the chopper to the total time
period of the chopper. It is denoted by .
PART-B
1. Discuss the working of 1_ two pulse bridge converter with RLE load using
relevant waveforms. (16)
2. A 1_ two pulse bridge converter feeds power to RLE load with R=6_, L= 6mH,
E = 60v, ac source voltage is 230v, 50Hz for continuous conduction. Find the
average value of load current for firing angle of 50 °. In case one of four SCR‟S
gets open circuited. Find the new value of average load current assuming the
output current as continuous. (16)
3. a) Explain the operation of 1_ semi converter and derive the expressions for its
average and rms output voltage. (8)
3. b) Derive the expressions for harmonic , displacement and power factor of a 1_ full
converter from the fundamental principle. (8)
4. Explain the working of 1_ full converter with RL load and derive the expression
for the average and rms value. (16)
UNIT-III
DC TO DC CONVERTER
1. What are the two types of control strategies?
a. Time Ratio Control (TRC)
b. Current Limit Control method (CLC)
2. What is meant by TRC?
In TRC, the value of Ton / T is varied in order to change the average output
voltage.
3. What are the two types of TRC?
a. Constant frequency control
b. Variable frequency control
4. What is meant by FM control in a dc chopper?
In frequency modulation control, the chopping frequency f (or the chopping
period T) is varied. Here two controls are possible.
a. On-time Ton is kept constant
b. Off period Toff is kept constant.
7
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7. 5. What is meant by PWM control in dc chopper?
In this control method, the on time Ton is varied but chopping frequency is kept
constant. The width of the pulse is varied and hence this type of control is known as Pulse
Width Modulation (PWM).
6. Write down the expression for the average output voltage for step down and step up
chopper.
Average output voltage for step down chopper is VO = VS. Average output
voltage for step up chopper is VO = VS x [ ( 1- )]1/.
7. What are the different types of chopper with respect to commutation process?
a. Voltage commutated chopper.
b. Current commutated chopper.
c. Load commutated chopper.
8. What is meant by voltage commutation?
In this process, a charged capacitor momentarily reverse biases the conducting
thyristor and turn it off.
9. What is meant by current commutation?
In this process, a current pulse is made to flow in the reverse direction through the
conducting thyristor and when the net thyristor current becomes zero, it is turned off.
10. What is meant by load commutation?
In this process, the load current flowing through the thyristor either becomes zero or
is transferred to another device from the conducting thyristor.
11. What are the advantages of current commutated chopper?
a. The capacitor always remains charged with the correct polarity.
b. Commutation is reliable as load current is less than the peak commutation current
ICP.
c. The auxiliary thyristor TA is naturally commutated as its current passes through
zero value.
12. What are the advantages of load commutated chopper?
a. Commutating inductor is not required.
b. It is capable of commutating any amount of load current.
c. It can work at high frequencies in the order of kHz.
d. Filtering requirements are minimal.
13. What are the disadvantages of load commutated chopper?
a. For high power applications, efficiency becomes very low because of high
switching losses at high operating frequencies.
b. Freewheeling diode is subjected to twice the supply voltage.
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8. c. Peak load voltage is equal to twice the supply voltage.
d. The commutating capacitor has to carry full load current at a frequency of half
chopping frequency.
e. One thyristor pair should be turned-on only when the other pair is commutated.
This can be realized by sensing the capacitor current that is alternating.
14. What is meant by inverter?
A device that converts dc power into ac power at desired output voltage and
frequency is called an inverter.
15. What are the applications of an inverter?
a. Adjustable speed drives
b. Induction heating
c. Stand-by aircraft power supplies
d. UPS
e. HVDC transmission
16. What are the main classification of inverter?
a. Voltage Source Inverter
b. Current Source Inverter
17. Why thyristors are not preferred for inverters?
Thyristors require extra commutation circuits for turn off which results in increased
complexity of the circuit. For these reasons thyristors are not preferred for inverters.
18. How output frequency is varied in case of a thyristor?
The output frequency is varied by varying the turn off time of the thyristors in the
inverter circuit, i.e. the delay angle of the thyristors is varied.
19. Give two advantages of CSI.
a. CSI does not require any feedback diodes.
b. Commutation circuit is simple as it involves only thyristors.
20. What is the main drawback of a single phase half bridge inverter?
It require a 3-wire dc supply.
PART – B
1. Discuss the principle of operation of DC-DC step down chopper with suitable
waveforms. Derive the expression for its average dc voltage. (16)
2. A step down dc chopper has input voltage of 230v with 10 ohm load, voltage
drop across chopper is 2v, when it is on. For a duty cycle of 0.5.
9
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9. Calculate i) average and rms value of output voltage ii) power delivered to the
load. (16)
3. Explain the two quadrant dc chopper operation with RLE load using suitable
waveforms. (16)
4. a) Explain time ratio control and current limit control strategies. (8)
b) Explain the resonant switching based SMPS. . (8)
5. Explain any one type of switched mode regulator and derive the expression
for it. (16)
UNIT-IV
INVERTERS
1. Why diodes should be connected in antiparallel with the thyristors in inverter
circuits?
For RL loads, load current will not be in phase with load voltage and the diodes
connected in anti parallel will allow the current to flow when the main thyristors are turned
off. These diodes are called feedback diodes.
2. What types of inverters require feedback diodes?
VSI with RL load.
3. What is meant a series inverter?
An inverter in which the commutating elements are connected in series with the
load is called a series inverter.
4. What is the condition to be satisfied in the selection of L and C in a series inverter?
R2 4L
5. What is meant a parallel inverter?
An inverter in which the commutating elements are connected in parallel with the
load is called a parallel inverter.
6. What are the applications of a series inverter?
The thyristorised series inverter produces an approximately sinusoidal waveform at a high
output frequency, ranging from 200 Hz to 100kHz. It is commonly used for fixed output
applications such as
a. Ultrasonic generator.
b. Induction heating.
c. Sonar Transmitter
d. Fluorescent lighting.
7. How is the inverter circuit classified based on commutation circuitry?
a. Line commutated inverters.
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10. b. Load commutated inverters.
c. Self commutated inverters.
d. Forced commutated inverters.
8. What is meant by McMurray inverter?
It is an impulse commutated inverter which relies on LC circuit and an auxiliary
thyristor for commutation in the load circuit.
9. What are the applications of a CSI?
a. Induction heating
b. Lagging VAR compensation
c. Speed control of ac motors
d. Synchronous motor starting.
10. What is meant by PWM control?
In this method, a fixed dc input voltage is given to the inverter and a controlled
ac output voltage is obtained by adjusting the on and off periods of the inverter
components. This is the most popular method of controlling the output voltage and this
method is termed as PWM control
.
11. What are the advantages of PWM control?
a. The output voltage can be obtained without any additional components.
b. Lower order harmonics can be eliminated or minimized along with its output
voltage control. As the higher order harmonics can be filtered easily, the filtering
requirements are minimized.
12. What are the disadvantages of the harmonics present in the inverter system?
a. Harmonic currents will lead to excessive heating in the induction motors. This
will reduce the load carrying capacity of the motor.
b. If the control and the regulating circuits are not properly shielded, harmonics
from power ride can affect their operation and malfunctioning can result.
c. Harmonic currents cause losses in the ac system and can even some time produce
resonance in the system. Under resonant conditions, the instrumentation and
metering can be affected.
d. On critical loads, torque pulsation produced by the harmonic current can be
useful.
13. What are the methods of reduction of harmonic content?
a. Transformer connections
b. Sinusoidal PWM
c. Multiple commutation in each cycle
d. Stepped wave inverters
14. Compare CSI and VSI.
S. No. VSI CSI
11
EE2301–POWERELECTRONICS
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11. 1.Input voltage is maintained Constant
Input current is constant but adjustable
2.The output voltage does not depend on the load The output current does not
depend on the load
3.The magnitude of the output current and its waveform depends on the nature of
the load impedance The magnitude of the output voltage
and its waveform depends on the nature of the load impedance
4.It requires feedback diodes It does not requires feedback diodes
5. Commutation circuit is complicated i.e. it contains capacitors and inductors.
Commutation circuit is simple i.e. it contains only capacitors.
15. What are the disadvantages of PWM control?
SCRs are expensive as they must possess low turn-on and turn-off times.
16. What does ac voltage controller mean?
It is device which converts fixed alternating voltage into a variable voltage
without change in frequency.
17. What are the applications of ac voltage controllers?
a. Domestic and industrial heating
b. Lighting control
c. Speed control of single phase and three phase ac motors
d. Transformer tap changing
18. What are the advantages of ac voltage controllers?
a. High efficiency
b. Flexibility in control
c. Less maintenance
19. What are the disadvantages of ac voltage controllers?
The main draw back is the introduction of harmonics in the supply current and the
load voltage waveforms particularly at low output voltages
.
20. What are the two methods of control in ac voltage controllers?
a. ON-OFF control
b. Phase control
PART – B
1. Explain the operation of single phase half bridge inverter with a neat
sketch. (16)
2. The single phase half bridge inverter has resistive load of R=10 ohm and dc
input voltage is 220v. Determine rms output voltage, average value, rms
current and output power. (16)
3. Explain the operation of single phase full bridge inverter with neat
sketch. (16)
3ndYEAR/ 5thSEMESTER
Fatima Michael College of Engineering Technology
Fatima Michael College of Engineering Technology
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12. 4. The single phase full bridge inverter has resistive load of R=2.4 ohm and dc
input voltage is 48v. Determine rms output voltage at the fundamental
frequency, output power. And the total harmonic distortion. (16)
5. Describe the working of three phase inverter with suitable waveform (16)
UNIT-V
AC TO AC CONVERTERS
1. What is the difference between ON-OFF control and phase control?
ON-OFF control: In this method, the thyristors are employed as
switches to connect the load circuit to the source for a few cycles of the load voltage and
disconnect it for another few cycles. Phase control: In this method, thyristor switches
connect the load to the ac source for a portion of each half cycle of input voltage.
2. What is the advantage of ON-OFF control?
Due to zero-voltage and zero current switching of thyristors, the harmonics
generated by the switching action are reduced.
3. What is the disadvantage of ON-OFF control?
This type of control is applicable in systems that have high mechanical inertia and
high thermal time constant.
4. What is the duty cycle in ON-OFF control method?
Duty cycle K = n/ (n + m), where n = no. of ON cycles, m = no. of OFF cycles.
5. What is meant by unidirectional or half-wave ac voltage controller?
Here the power flow is controlled only during the positive half-cycle of the input
voltage.
6. What are the disadvantages of unidirectional or half-wave ac voltage controller?
a. Due to the presence of diode on the circuit, the control range is limited and the
effective RMS output voltage can be varied between 70.7% and 100%.
b. The input current and output voltage are asymmetrical and contain a dc
component. If there is an input transformer, saturation problem will occur
c. It is only used for low power resistive load.
7. What is meant by bidirectional or half-wave ac voltage controller?
Here the power flow is controlled during both cycles of the input voltage.
8. What is the control range of firing angle in ac voltage controller with RL load?
The control range is F a 180°, where F = load power factor angle.
13
EE2301–POWERELECTRONICS
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Fatima Michael College of Engineering Technology
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13. 9. What type of gating signal is used in single phase ac voltage controller with RL
load?
High frequency carrier gating signal is used for single phase ac voltage controller
with RL load.
10. What are the disadvantages of continuous gating signal?
a. More heating of the SCR gate.
b. Increases the size of pulse transformer.
11. What is meant by high frequency carrier gating?
Thyristor is turned on by using a train of pulses from a to p. This type of signal
is called as high frequency carrier gating.
12. What is meant by sequence control of ac voltage regulators?
It means that the stages of voltage controllers in parallel triggered in a proper
sequence one after the other so as to obtain a variable output with low harmonic content.
13. What are the advantages of sequence control of ac voltage regulators?
a. System power factor is improved.
b. Harmonics are reduced in the source current and the load voltage.
14. What is meant by cyclo-converter?
It converts input power at one frequency to output power at another frequency
with one-stage conversion. Cycloconverter is also known as frequency changer.
15. What are the two types of cyclo-converters?
a. Step-up cyclo-converters
b. Step-down cyclo-converters
16. What is meant by step-up cyclo-converters?
In these converters, the output frequency is less than the supply frequency.
17. What is meant by step-down cyclo-converters?
In these converters, the output frequency is more than the supply frequency.
18. What are the applications of cyclo-converter?
a. Induction heating
b. Speed control of high power ac drives
c. Static VAR generation
3ndYEAR/ 5thSEMESTER
Fatima Michael College of Engineering Technology
Fatima Michael College of Engineering Technology
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14. d. Power supply in aircraft or ship boards
19. What is meant by positive converter group in a cyclo converter?
The part of the cycloconverter circuit that permits the flow of current during
Positive half cycle of output current is called positive converter group.
20. What is meant by negative converter group in a cyclo converter?
The part of the cyclo converter circuit that permits the flow of current during
negative half cycle of output current is called negative converter group.
PART-B
1. Draw the circuit diagram of 1_ capacitor commutated current source inverter
and explain its operation with equivalent circuits for different modes and
necessary waveforms.
2. Explain the operation of multistage control of AC voltage controllers with neat
diagram.
3. .Explain the operation of 1_ AC voltage controller with RL load.
4. Explain the operation of sequence control of AC voltage controller..
5. Explain the operation of 1_ sinusoidal AC voltage controller..
6. For a 1_ voltage controller, feeding a resistive load, draw the waveforms of source
voltage, gating signals, output voltage and voltage across the SCR. Describe the working
with reference to waveforms drawn.
15
EE2301–POWERELECTRONICS
Fatima Michael College of Engineering Technology
Fatima Michael College of Engineering Technology
www.studentsfocus.com