Subject Code : EE6503 Branch : EEE

Subject Name : Power Electronics Year/Sem. : III /V

Unit - I PART-A

1. State the advantages of IGBT over MOSFET. (Nov/Dec 2008)

2. What is the function of snubber circuit? (Nov/Dec 2008, 2013, May/June 2013)

3. How SCR differs from TRIAC? (May/June 2009, Nov/Dec 2014)

4. What is snubber circuit? (May/June 2009)

5. Draw the characteristics of TRIAC and mark the timings td, tr and ton. (Nov/Dec 2010)

6. What are the factors that influence the turn off time of a thyristor? (Nov/Dec 2010)

7. State the condition to be satisfied for the load commutation in SCR. (Nov/Dec 2011)

8. Define “Turn off time” of SCR. (Nov/Dec 2011)

9. What are the drawbacks of GTO? (Nov/Dec 2012)

10. Why are IGBT becoming popular in their application to controlled converters?

(May/June

2012)

11. Define the term pinch off voltage of MOSFET. (May/June 2012)

12. List the various forced commutation techniques used to turn off SCR. (Nov/Dec 2013)

13. Define Latching current and Holding current. (Nov/Dec 2012, May/June 2014)

14. Compare power MOSFET and BJT. ( May/June 2014)

15. What is meant by current commutation of SCR? (Nov/Dec 2014)

16. What is the limitation of high frequency operation of a power electronic device?

(May/June 2013)

17. Write the advantages of GTO over SCR.

18. What is the importance of snubber in thyristor protection?

19. Draw the reverse recovery characteristics of diode.

20. What are switching devices? (Nov/Dec 2016)

21. Draw a meat sletcj pf Turn On characteristics of SCR. (Nov/Dec 2016)

22. Why are IGBT becoming popular in PE Based applications? (May/June 2017)

23. Define the term pinch off voltage of MOSFET. (May/June 2017)

PART-B

1. Explain the structure, different modes of operation and characteristics of Triac.

(Nov/Dec 2008)

2. Describe about any one driver circuit and snubber circuit for MOSFET.

(Nov/Dec 2008, May/June 2012)

3. (a)Compare the performance characteristics of MOSFET and BJT. (8) (May/June

2009) (b)Briefly discuss the V-I characteristics of SCR. (8) (May/June 2009, 2014,

May/June 2012)

4. Explain the turn-on and turn-off characteristics of IGBT with neat waveforms. (May/June

2009)

5. Explain the operation of IGBT with the help of neat structural diagram and suitable

waveforms. (Nov/Dec 2010)

6. (a)Explain the operation of SCR using two transistor analogy. (8) (May/June 2014)

(b)What are the different methods for turning off an SCR? Explain all methods in

detail. (Nov/Dec 2010)

7. Describe the current commutation technique to turn off the SCR with neat sketch and

waveforms. (Nov/Dec 2011)

8. With neat sketch explain the turn-on and turn-off characteristic of SCR.

(Nov/Dec 2011, 2010, May/June 2013)

9. (a)Compare and contrast the performance characteristics of SCR and MOSFET. (8)

(Nov/Dec 2012)

(b)Discuss any two types of commutation circuits used for SCR in detail. (8)

(Nov/Dec 2012, May/June 2013)

10. Discuss in detail the static and switching characteristics of IGBT. (Nov/Dec 2012, 2014)

11. (a)Draw and explain the switching characteristics of SCR. (8) (Nov/Dec 2013) (Nov/Dec

2016)

(b)Discuss the working of a complementary commutation circuit of SCR with a

neat circuit diagram and waveforms. (8) (Nov/Dec 2013)

12. Describe the basic structure of IGBT and explain its working. Give its equivalent

circuit and explain the turn ON and turn OFF processes. (Nov/Dec 2013)

13. (a)Explain the switching characteristics of power MOSFET. (8)

(May/June 2014, Nov/Dec 2014)

(b)Briefly explain about the power MOSFET protection circuits. (8) (May/June 2014)

14. (a)Explain why TRIAC is rarely operated in I quadrant with –Ve gate current and in

III quadrant with +Ve gate current. (8) (May/June 2012)

(b)Snubber circuit for an SCR should primarily consists of capacitor only. But in

practice a resistor is used in series with the capacitor. Why? Discuss. (8) (May/June

2013)

15. Discuss the different turn-on methods of SCR with its turn-on characteristics. (Nov/Dec

2014)

16. Draw neat diagrams of Derive the snubber circuits of TRIAC and IGBT and explain the

working and application. (Nov/Dec 2016) (May/June 2017)

17. Discuss the different modes of operation of thyristor with the help of its static VI

characteristics. (May/June 2017)

18. Explain why triac is rarely operated in I quadrant with –ve gate current and in III

quadrant with +ve gate current. (May/June 2017)

UNIT – II

PART - A

1. Write the expression for output dc voltage in a single phase fully controlled converter.

(Nov/Dec 2008)

2. Define Total Harmonic Distortion. (Nov/Dec 2008, May/June 2012)

3. Define Distortion factor. (May/June 2009)

4. What is inversion mode of rectifiers? (May/June 2009, Nov/Dec 2012)

5. Draw the circuit diagram of single phase dual converter. (Nov/Dec 2010)

6. Define the term voltage ripple factor, current ripple factor. (Nov/Dec 2010)

7. Give any two differences between single phase full converter and semi converter. (Nov/Dec 2011, May/June 2014)

8. What is meant by line commutated inverter? (Nov/Dec 2011)

9. Under what conditions a single phase fully controlled converter gets operated as an Inverter.

(May/June 2012)

10. Why is power factor of semi converter better than full converter? (Nov/Dec 2012, 2014)

11. Mention the disadvantages of dual converter with circulating current mode of operation.

(Nov/Dec 2013)

12. A single phase full converter feeds power to RLE load with R = 6Ω and E = 60V. The

load inductance value is very large so as to maintain the load current continuous and

ripple free. The ac source voltage is 230V and 50Hz. Find the average value of the

output voltage for a firing angle delay of 50o. (Nov/Dec 2013)

13. What is dual converter? Mention its functional mode of operation. (May/June 2014)

14. What is meant by phase control? (Nov/Dec 2014)

15. What is displacement factor for two pulse converter? (May/June 2013)

16. What is circuit turn-off time for single phase full converter? (May/June 2013)

17. Write the significance of free wheeling diode.

18. What is the principle of a phase control?

19. Draw a neat sketch of Battery Charget. (Nov/Dec 2016)

20. What is meant by phase controlled converters? (Nov/Dec 2016)

PART-B

1. With necessary circuit and waveforms, explain the principle of operation of 6-pulse converter.

Derive the expression for average output voltage in it. (Nov/Dec 2008, May/June 2012) 2. (a)Explain the effect of source inductance in the operation of single phase fully controlled

converter. (8) (Nov/Dec 2008)

(b)Describe the working principle of single phase AC voltage controller with circuit and

waveforms. (8) (Nov/Dec 2008)

3. Explain the operation of three phase full converter. Also derive the expression for its average

output voltage. (May/June 2009)

4. A single phase full wave AC voltage controller has an input voltage of 230V, 50Hz and it is

feeding a resistive load of 10Ω. If firing angle of thyristors is 110 o, find the output RMS

voltage, input power factor and average current of thyristor. (May/June 2009)

5. (a) Describe the operation of a single phase two pulse bridge converter using 4 SCR’s with

relevant waveforms. (10) (Nov/Dec 2010)

(b) Discuss the working of above converter in the converter mode with RLE load. (6)

(Nov/Dec 2010) 6. (a)A single phase semi converter is operated from 120V, 50Hz, AC supply. The load current

with an average value Idc is continuous and ripple free firing angle α = 6. Determine

(i) Displacement factor. (ii) Harmonic factor of input current. (iii) Input power factor. (10)

(Nov/Dec 2010)

(b) Describe briefly the working of Dual converter with a neat circuit diagram. (8)

(Nov/Dec 2013, 2014)

7. Explain the working of a three phase full converter with R load for the firing angles of 60o,

90o and 150

o. (Nov/Dec 2011)

8. (a)Explain the operation of a single phase full bridge converter with RL load for

continuous and discontinuous load currents. (10) (Nov/Dec 2011)

(b)A single phase full bridge converter is connected to R load. The source voltage is of 230V,

50Hz. The average load current is of 10A. For R = 20Ω find the firing angle. (6)

(Nov/Dec 2011) 9. Explain the operation of three phase semi converter with neat waveforms. (Nov/Dec 2012)

10. Describe the working of a single phase full converter in the rectifier mode with RL load.

Discuss how one pair of SCR’s is commutated by an incoming pair of SCR’s. Illustrate your

answer with the waveforms of source voltage, load voltage and source current. Assume

continuous conduction. Also derive the expressions for average and rms output voltage.

(Nov/Dec 2013)

11. (a)A single phase two pulse bridge converter feeds power to RLE load with R=6Ω, L=6mH,

E=60V, AC source voltage is 230V, 50Hz for continuous conduction. Find the average

value of load current for a firing angle of 50o. Incase one of the 4 SCR’s gets open

circuited. Find the new value of average load current assuming the output current as

continuous. (10) (May/June 2012)

(b)Describe the operation of a single phase two pulse bridge converter in the inverter

mode with RLE load. (6) (May/June 2012)

12. A 220V, 1KW resistive load is supplied by 220V, 50Hz source through single phase fully

controlled rectifier. Determine the following for 800W output. (i) output voltage. (ii) rms value

of input current. (iii) fundamental component of input current. (iv) displacement factor.

(Nov/Dec 2012) 13. Discuss the effect of source inductance on the performance of single phase full converter.

(May/June 2013, 2014)

14. Explain the two functional modes of Dual converter with necessary diagrams.

(May/June 2013, 2014)

15. A 230V, 50Hz supply is connected to load resistance of 12Ω through half wave controlled

rectifier. If the firing angle is 60o, determine Average output voltage, rms output voltage,

Ratio of rectification and Transformer utilization factor. (Nov/Dec 2014)

16. (a)A single phase bridge converter is utilized to produce regulated DC output voltage. The

input voltage is 230V and the load current is 8A for a firing angle of 30o.

(i)Calculate the DC output voltage. (4)

(ii)Calculate the DC output voltage and current if a freewheeling diode is used at the

output for the same firing angle as in (i). (4) (May/June 2013)

(b)Explain single phase half wave rectifier circuit with RL load and freewheeling diode. (8)

(May/June 2013)

17. Compare 3 pulse and 6 pulse converters. (Nov/Dec 2016)

18. Explain the effect of source inductance of a 3 pulse converters. (Nov/Dec 2016)

19. Determine the performance parameters of a phase controlled converter. (Nov/Dec 2016)

20. Write a short notes on Dual converters (Nov/Dec 2016)

21. Explain the operation of single phase controlled rectifier which can be operated in

rectification and inversion mode. Derive the performance parameters Pn AC side for above

converter in rectification mode. (May/June 2017)

22. A 3 phase 6 pulse fully converter is connected to resistive and inductive load of 10 ohms

and 1H respectively from 3 phase, 220V, 50Hz, star connected supply. For firing angle of 30 ,

determine.. (i) Average output voltage, (ii) Average output current, (iiik) RMS output current.

(May/June 2017)

Unit - III PART-A

1. What is meant by time ratio control in chopper? (Nov/Dec 2008, 2013) 2. Write any two salient features of CUK converter. (Nov/Dec 2008) 3. What is cuk converter? (May/June 2009) 4. What is meant by SMPS? (May/June 2009) 5. Mention any two disadvantages of frequency modulation control strategy. (Nov/Dec 2010) 6. What are the advantages of ZVS when compared to ZCS? (Nov/Dec 2010) 7. What are the advantages of SMPS over phase controlled rectifiers? (Nov/Dec 2011) 8. Give the uses of resonant switching. (Nov/Dec 2011) 9. Brief up the working of four quadrant DC chopper. (Nov/Dec 2012) 10. What is constant frequency control of chopper? (Nov/Dec 2012) 11. Define the term Inverter gain. (May/June 2012) 12. What is a DC chopper? (Nov/Dec 2013, May/June 2012) 13. What are the advantages and disadvantages of cuk converter? (May/June 2014) 14. What are the circuit configurations used for SMPS? (May/June 2014) 15. Write the applications of DC chopper. (Nov/Dec 2014) 16. Distinguish between time ratio control and current limit control employed in a DC

chopper. (Nov/Dec 2014) 17. What are the control strategies for chopper circuit? (May/June 2013) 18. What is the need for resonant converter? (May/June 2013) 19. What is meant by forced commutation? 20. Write down two disadvantages of voltage commutated chopper.

21. Give any two advantages of DC to DC converter. (Nov/Dec 2016)

22. Name any two applications of SMPS. (Nov/Dec 2016)

23. What is constant frequency control of chopper? (May/June 2017)

24. Briefly state the working of four quadrant DC chopper. (May/June 2017)

PART-B

1. With necessary circuits and waveforms, explain the principle of operation of stepdown DC

to DC converter with RL load. (Nov/Dec 2008, 2010)

2. Describe the working principle of boost converter with necessary circuit and waveforms.

(Nov/Dec 2008, May/June 2012)

3. (a)A DC chopper has an input voltage of 200V and a load of 15Ω resistance. When chopper is

ON, its voltage drop is 1.5V and the chopping frequency is 10KHz. If the duty cycle is 80%,

find (i) Average output voltage, (ii) RMS output voltage and (iii) Chopper ON time. (12)

(May/June 2009)

(b)Prove the output voltage of step down chopper is Vo = DVs. (4) (May/June 2009) 4. Explain the operation of boost and buck-boost converter with neat circuit diagram and

waveforms. (May/June 2009)

5. Draw the circuit of CUK regulator and explain its working principle with necessary waveform

in detail. (Nov/Dec 2010)

6. Explain the working of Buck-Boost converter with sketch and waveforms and also derive the

expression for Is. (Nov/Dec 2011)

7. Discuss the operation of DC-DC boost converter and prove that its output voltage is always

greater than input voltage. (Nov/Dec 2012, May/June 2013)

8. A voltage commutated chopper circuit provides the speed control of DC separately excited

motor. The source voltage is 80V. The starting current is 60A and thyristor turn-off time is

20µs. Calculate the values of commutating capacitor and inductor if chopping period is

2000µs. (Nov/Dec 2012)

9. (a)A type-A chopper has supply voltage Vs and duty cycle of (A) 0.4 and (b) 0.6. For these

duty cycles, Calculate

(i) average and rms values of output voltage. (3)

(ii) output power for R load. (3)

(iii) ripple factor. (2). (May/June 2013)

(b) A stepdown DC chopper has a resistive load of R = 15Ω and input voltage Edc = 200V.

When the chopper remains ON, its voltage drop is 2.5 for a duty cycle of 0.5. Calculate

(i)Average and rms value of output voltage. (ii) Power delivered to the load. (8) (Nov/Dec

2010)

10. (a) A DC battery is charged from a constant DC source of 220V through a chopper. The DC

battery is to be charged from its internal emf of 90V to 122V. The battery has internal

resistance of 1Ω. For a constant charging current of 10A, compute the range of duty cycle. (8)

(Nov/Dec 2013)

(b)Draw the power circuit diagram of a buck regulator and explain its operation with

equivalent circuit for different modes and waveforms. (8) (May/June 2013)

11. (a)Explain the principle of a step up chopper with neat circuit diagram and necessary

waveforms. Derive the expressions for its average output voltage. (10) (Nov/Dec

2013, 2014) (b)Write short note on resonant switching. (6) (Nov/Dec 2013)

12. Explain the operation of class C and class D types of two quadrant choppers. (May/June

2014)

13. Draw the power circuit diagram of Cuk regulator and explain its operation with

equivalent circuit for different modes with necessary waveforms. (May/June 2014)

14. A step up chopper has input voltage of 220V and output voltage of 660V. If the

nonconducting time of thyristor chopper is 100µs compute the pulse width of output

voltage. Incase the pulse width is halved for constant frequency operation. Find the

new output voltage. Derive the expressions used in the above problem with necessary

waveform. (May/June 2012)

15. A DC chopper has an input voltage of 200V and a load of 8Ω resistance. The voltage

drop across thyristor is 2V and the chopping frequency is 800Hz. The duty cycle is

0.5. Find the Average output voltage, RMS output voltage, Chopper efficiency and

Input resistance seen by the source. (Nov/Dec 2014)

16. Describe with neat diagrams the principle and working of Buck-Boost converter.

(Nov/Dec 2016)

17. What is called resonant switching? Explain its concept with relevant circuit diagram.

(Nov/Dec 2016)

18. A type A chopper has supply voltage Vs and duty cycle 0.4 and 0.6 for these duty cycle,

find,

(i) Average and rms values of output voltage, (ii) output power for R load of 120 ohms

(iii) Ripple factor(May/June 2017)

19. Explain the operation of step up chopper and derive and expression for its output voltage.

(May/June 2017)

Unit – IV PART-A

1. Mention the difference between sinusoidal PWM and modified sinusoidal PWM techniques.

(Nov/Dec 2008)

2. What is meant by current source inverter? (Nov/Dec 2008,2011,2012,2016, May/June

2009)

3. List the advantages of multiple PWM over single PWM technique. (May/June 2009)

4. Differentiate VSI from CSI. (Nov/Dec 2010, May/June 2012, 2014)

5. List various applications of phase controlled converters. (Nov/Dec 2010)

6. Why is series inverter called so? (Nov/Dec 2011)

7. What are the advantages of PWM inverters? (Nov/Dec 2012)

8. What is the advantage of 120o mode of inverter operation over 180

o mode? (Nov/Dec 2013)

9. List the various advantages of using PWM control to inverters?

(Nov/Dec 2013, May/June 2014)

10. Define the term Inverter gain. (May/June 2012)

11. What is meant by Voltage Source Inverter. (Nov/Dec 2014)

12. Write the advantages of resonant converters. (Nov/Dec 2014)

13. In a CSI, if frequency of output voltage is f Hz, what is the frequency of voltage input to

CSI? (May/June 2013)

14. What is space vector? (May/June 2013)

15. What is an inverter?

16. What is the principle of inversion?

17. Differentiate line and load commutation.

18. Distinguish between 120o and 180

o mode of conduction.

19. What is PWM?

20. Write the types of PWM.

21. What are the types of PWM techniques.? (Nov/Dec 2016)

22. Compare SPWM and SVM. (May/June 2017)

23. In a CSI, if frequency of output voltage is F hz, what is the input frequency of CSI?

(May/June 2017)

PART-B

1. Explain the principle of operation of three phase inverter with 180o conduction mode with

necessary waveforms and circuit. (Nov/Dec 2008)

2. (a)Describe any one PWM technique used in inverter in detail. (8) (Nov/Dec 2008)

(b)Explain the working principle of single phase current source inverter. (8)

(Nov/Dec 2008, May/June 2012)

3. Discuss the functioning of three phase voltage source inverter in 120o operating mode.

(May/June 2009,2014,2017, Nov/Dec 2012)

4. Explain, different methods of voltage control adapted in an inverter with suitable waveforms.

(May/June 2009)

5. (a)Describe the working of a single phase full bridge inverter with relevant circuit and

waveforms. (8) (Nov/Dec 2010)

(b)What is PWM? List the various PWM techniques and explain any one of them. (8) (Nov/Dec 2010, 2016) (May/June 2017) 6. Explain the harmonic reduction by transformer corner lines and stepped wave inverters.

(Nov/Dec 2010) 7. With a neat sketch and output voltage waveforms, explain the working of three phase bridge

inverter in 180o mode of operation. (Nov/Dec 2011, 2014)

8. Explain in detail, the various types of PWM methods employed in an inverter.

(Nov/Dec 2012,2014, May/June 2014)

9. With a neat diagram and waveforms explain three phase VSI using transistors operating in

120o conduction mode. Also obtain the expression for rms value of output voltage.

(May/June 2013)

10. Explain Multiple Pulse Width Modulation and Sinusoidal Pulse Width Modulation.

(May/June 2013) 11. Discuss the principle of working of a three phase bridge inverter with an appropriate circuit

diagram. Draw the output phase and line voltage waveforms on the assumption that each

thyristor conducts for 180o and resistive load is star connected. The sequence of firing of

various SCR should also be indicated. (Nov/Dec 2013)

12. Write short notes on Sinusoidal pulse width modulation as applied to inverters and Current

source inverters. (Nov/Dec 2013)

13. Write in detail about voltage and harmonic control with neat diagram. (Nov/Dec 2016)

Unit - V

PART-A

1. Name the different topologies of uninterrupted power supply. (Nov/Dec 2008)

2. What is the function of static VAR compensator? (Nov/Dec 2008)

3. What is the need for UPFC? (May/June 2009)

4. What is off-line UPS? (May/June 2009)

5. What is meant by cyclo converter? (Nov/Dec 2010,2014, May/June 2012)

6. Write the output RMS voltage for single phase AC voltage controller with resistance load.

(Nov/Dec 2010)

7. What are the applications of cyclo converter? (Nov/Dec 2011)

8. What is integral cycle control? (Nov/Dec 2011,2014, May/June 2012)

9. Write the principle of operation of cyclo converter. (Nov/Dec 2012)

10. Give any two applications of AC voltage controllers. (Nov/Dec 2012)

11. What is a matrix converter? (Nov/Dec 2013, May/June 2013, 2014)

12. Enumerate some of the industrial applications of a cyclo converter. (Nov/Dec 2013)

13. What is the control range of firing angle in AC voltage controller with R-L load?

(May/June 2014)

14. What are the types of AC voltage controllers? (May/June 2013)

15. What is meant by ON-OFF control and phase angle control?

16. Write the classifications of AC Voltage controllers.

17. Define blocked mode and circulating mode.

18. Write two advantages of phase angle control.

19. Write the output RMS voltage for single phase AC voltage controller with resistive load.

20. Mention the advantages of matrix converter over AC-DC-AC converters.

21. List the disadvantages of an AC voltage controller.

22. What are called Matrix converters? (Nov/Dec 2016)

23. What is the advantage of AC to AC converters? (Nov/Dec 2016)

PART-B

1. With neat circuit diagrams, explain the operation of switched mode and resonant AC power

supplies used in UPS. (Nov/Dec 2008)

2. Explain the construction and principle of operation of static VAR compensator.

(Nov/Dec 2008)

3. Discuss the operation of on-line and off-line UPS with block diagram. (May/June 2009)

4. Write short notes on HVDC transmission and static VAR compensator. (May/June 2009)

5. (a)Describe the operation of single phase full wave AC voltage controller with the help of

voltage and current waveform. Also derive the expression for average value of output

voltage. (10) (Nov/Dec 2010)

(b)For a single phase AC regulator feeding a resistance load, show that power factor is given

by the Expression √[ 1 (∏-x)+ 2 ] (6) (Nov/Dec 2010)

∏

2

6. Describe three phase to three phase cycloconverter with relevant circuit arrangement using

18 thyristors. (8) (Nov/Dec 2010)

7. Discuss the working of 2 stage sequence control of AC voltage controller. (Nov/Dec 2011)

8. Discuss the working of a three phase to single phase cyclo converter with neat voltage and

current waveforms. (Nov/Dec 2011, 2012,2014, May/June 2012, 2014)

9. A resistive load of 5Ω is fed through a single phase full wave AC voltage controller from

230V, 50Hz source. If firing angle of thyristors is 120o , find the output RMS voltage, input

power factor and average current of thyristor. (Nov/Dec 2012)

10. Describe the basic principle of working of single phase to single phase step down cyclo

converter for a bridge type converter. Assume both discontinuous and continuous conduction

and draw the load current and load voltage waveforms for both the cases. Mark the conduction

of various thyristors. (Nov/Dec 2013,2014)

11. Write short notes on Power factor control, Multistage sequence control, step up cyclo

converter and Matrix converter. (Nov/Dec 2013)

12. With the aid of circuit diagram and waveform explain the operation of Power factor control in

AC voltage regulation and single phase full wave AC voltage controller. (May/June 2014)

[ 13. Describe the principle of operation of PWM type and multistage sequential AC voltage

controller. (May/June 2012)

14. A single phase full wave AC voltage controller has an input voltage of 230V, 50Hz and it is

feeding a resistive load of 10Ω . If firing angle of thyristors is 110o, find the output RMS

voltage, input power factor and average current of thyristor. (Nov/Dec 2014)

15. What is the importance of power factor control in a converter? Explain in detail. (Nov/Dec

2016)

16. Write a short notes on Matrix converters (Nov/Dec 2016)

17. Describe the basic principle of working 1 phase to 1 phase step down bridge type

cycloconverter. Assume discontinuous and continuous conduction and draw the load current

and load voltage waveforms for both the cases. Mark the conduction of various thyristors.

(May/June 2013)

18. Write short note on the following: (i) Integral cycle control, (ii) Multistage sequence control, (iii)

Step up cyclo converter, (iv) Matrix converter. (May/June 2013)