EE2301-POWER ELECTRONICS Questions Bank 2014

Anna University, Chennai

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M.A.M. SCHOOL OF ENGINEERING

SIRUGANUR, TRICHY – 621 105

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING EE2301-POWER ELECTRONICS

UNIT-I POWER SEMICONDUCTOR DEVICES PART-A

1. What are the different methods to turn on the thyristor?

2. Define latching current.

3. Define holding current.

4. What is a snubber circuit?

5. Why IGBT is very popular nowadays?

6. What is the difference between power diode and signal diode?

7. What is Thyristor? Mention some of them.

8. What are the advantages of GTO over SCR?

9. What losses occur in a thyristor during working conditions?

10.IGBT is a voltage controlled device. Why?

11.Power MOSFET is a voltage controlled device. Why?

12.Power BJT is a current controlled device. Why?

13.What are the different types of power MOSFET?

14.How can a thyristor turned off?

15. What losses occur in a thyristor during working conditions?

16.Define circuit turn off time.

17.Why circuit turn off time should be greater than the thyristor turn-off time?

18.What is the turn-off time for converter grade SCRs and inverter grade

SCRs?

19.What are the classifications of Power semiconductor devices?

20.Define Hard-firing or over driving.

21.Define forward Break over Voltage.

22.Define Reverse Break over voltage.

23.What is forced commutation?

24.What is meant by Secondary breakdown?

25.What are the advantages of TRIAC?

26.What are the disadvantages of TRIAC?

27.Compare Power MOSFET’s with BJT’s.

28. In TRIAC’s which of the modes the sensitivity of gate is high.

29.Define the term pinch off voltage of MOSFET.

30.What are the basic features of power MOSFET?

31.Distinguish between holding current and latching current of SCR.

32.What is commutation? What are the two main types of commutation?

33.Draw the V-I characteristics of SCR and mark the holding current and latching current in the characteristics.

34.Why MOSFET’s are not preferred for high frequency application?

35.What are the advantages of IGBT over MOSFET?

36.What are the classification of power Diodes?

37.What is reverse recovery time of Diodes?

38.What are the difference between SCR and TRIAC.

39.Define Spread Time.

40.What is the turn-off time for converter and inverter grade SCRs?

PART-B

1. Draw the two transistor model of SCR and derive an expression for anode

current.

2. Explain the Construction, principle of operation and static characteristics of

SCR

3. Describe the various methods of thyristor turn on.

4. Explain basic structure, characteristics and operation of MOSFET’s.

5.Explian detail in Structure, characteristics of TRIAC.

6.Explin detail in Construction of BJT and that characteristics.

7. Explain basic structures, characteristics and operation of IGBT’s.

8.Explin detail in GTO.

9. What are the types of special semiconductor devices? And Explain in detail.

10.Describe any one driver circuit and snubber circuit for MOSFET.

11.Explain the switching performance of BJT with relevant waveforms indicating clearly the turn-on, turn off times and their components.

12. Describe turn on characteristics of IGBT with neat waveforms.

13.What is commutation? What are the two types of commutation?

14. What are the different Modes of operation of TRIAC?

15.Sketch the transfer and switching characteristics of IGBT.

16. write short notes on i) snubber circuit for BJT

ii) Commutation circuit of SCR.


UNIT II

PHASE-CONTROLLED CONVERTERS

1. What is meant by phase controlled rectifier?

2. What is the function of freewheeling diodes in controlled rectifier?

3. What are the advantages of freewheeling diodes in a controlled in a controlled rectifier?

4. What is meant by delay angle?

5. What are the advantages of single phase bridge converter over single phase mid-point converter?

6. What is commutation angle or overlap angle?

7. What are the different methods of firing circuits for line commutated converter?

8. Give an expression for average voltage of single phase semiconverters.

9. What is meant by input power factor in controlled rectifier?

10.What are the advantages of six pulse converter?

11.What are the general classification of rectifier circuits?

12. What is meant by uncontrolled rectifier?

13.What are the different types of controlled rectifier?

14.What is meant by half controlled rectifier?

15.what is meant by full converter?

16.List various applications of controlled converters?

17.What are the two configuration of single phase two pulse controlled rectifier?

18.Give an expression for average output voltage of single phase full converter.

19. What is the inversion mode of rectifiers?

20.What are the advantages of single phase bridge converter over single phase mid-point converter?

21.What are the performance factors of line-commutated converters?

22.Define voltage ripple factor?

23. When does the line commutated converter act as a line commutated inverter?

24. How is power factor of semi converter better then that of full converter?

25.Draw the half controlled single phase converter circuit.

26.Draw a half wave AC to DC converter circuit and plot the output waveform for a = 90 . Assume resistance load.

27.Define harmonic factor or THD of the input current.

28. Define displacement factor.

29.What is three phase controlled rectifier?

30. What are the advantages of three phase controlled rectifier?

31.What are the classifications of three phase controlled rectifier?

32.Write down the expression for average output voltage of three phase half controlled rectifier?

33. Write down the expression for average output voltage of three phase full converter?

34.What are the effects of source impedance in the controlled rectifiers?

35. What is meant by continuous current operation of thyristor converter?

1. of fully controlled converter with resistive load and derive the expressions for various parameters.

2. Discuss operation of a single phase full wave controlled rectifier feeding RL load. What is the effect of adding a freewheeling diode on the performance of the converter.

3. Describe the working of 1 ф fully controlled bridge converter in the Rectifying mode and inversion mode. And derive the expressions for average output voltage and rms output voltage.

4. Describe the principle of operation of two pulse midpoint converter with

resistive load and also derive the average load voltage.

5. Explain the operation of full wave mid point converter with RL load.

6. With neat sketch, describe the function of single phase half controlled bridge rectifier with resistive load. what will the waveforms observed?

7. With neat sketch, describe the function of single phase half controlled bridge rectifier with resistive load and inductive load. what will the waveforms observed?

8. Derive the expressions for average output voltage and rms output voltage

of 1 ф semi converter.

9. With neat sketch, describe the function of single phase half controlled bridge rectifier with RLE load free-wheeling load. what will the waveforms observed?

10. Describe the operation three phase half wave controlled rectifier with

resistive load with continuous and discontinuous mode of operation.

11.Describe the operation and waveform of three phase half wave controlled rectifier with RL load.

12.Describe the operation and waveform of three phase half controlled

Bridge rectifier.

13. Describe the working of 3 ф fully controlled bridge converter in the Rectifying mode and inversion mode. And derive the expressions for average output voltage and rms output voltage.

14. Describe the working of Dual converter.

15. Explain the effect of source inductance on the performance of single phase fully controlled converter.

16.Explain the effect of source inductance on the performance of single phase fully controlled converter.

17.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 a = p/3. Determine.i) Displacement factor

ii) Harmonic factor of input current

iii) Input power factor

18.write a note on battery charger

19.Describe the effect of source inductance on the performance of a single phase full converter indicating clearly the conduction of various thyristors during one cycle. Derive the expression for its output voltage.

20.Explain the working of a three phase full converter with ‘R’ load for the firing angles of 60˚, 90 and 150˚.


UNIT III

DC TO DC CONVERTERS PART A

1. What is meant by dc chopper?

2. What are the applications of dc chopper?

3. What is meant by step-up and step-down chopper?

4. Write down the expression for average output voltage for step down

chopper.

5. Write down the expression for average output voltage for step up chopper.

6. What is meant by duty-cycle?

7. What are the two types of control strategies?

8. What is meant by TRC?

9. What are the two types of TRC?

10.What is meant by FM control in a dc chopper?

11.What are the advantages of dc chopper?

12.What are the classification of dc converters depending upon the directions of current and voltage?

13.What is meant by PWM control in dc chopper?

14.What are the disadvantages of frequency modulation scheme over the pulse width modulation scheme?

15.Define switched mode regulator.

16.What are the basic topologies of switching regulators?

17.What is meant by buck regulators?

18.What are the advantages and disadvantages of buck converter?

19.Define boost converter?

20.What are the applications of boost converter?

21.What are the advantages and disadvantages of boost converters?

22.Define Buck-Boost Converter.

23.What are the advantages and disadvantages of buck-boost regulator?

24.What is cuk converter?

25.Give the advantages and disadvantages of cuk regulator.

26.What are the different control techniques used in choppers?

27.Draw the circuit of cuk converter.

28.What are the classifications of chopper?

29.Why forced commutation used in chopper circuits?

30.What is meant by SMPS?

31.What is current limit control of a DC chopper?

32.What is the need for a filter at the output of a step up DC converter?

33.What is two quadrant DC chopper?

34.What is a resonant converter?

35. What the effects of chopping frequency on filter sizes?

36.What are advantages of resonant converters?

37.What is meant by zero voltage switching of resonant converters?

38.Sketch the diagram of a basic step up chopper.

39.Differentiate between constant frequency and variable frequency control strategies of varying the duty cycle of DC choppers.

40.What are the differences between Buck-Boost and Cuk converters?

PART B

1. Describe the principle of step-up chopper. Derive an expression for the average output voltage in terms of input dc voltage & duty cycle.

2. Describe the working of four quadrant chopper.

3. Explain the working of current commutated chopper with aid of circuit diagram and necessary waveforms. Derive an expression for its output voltage.

4. Explain the working of voltage commutated chopper with aid of circuit diagram and necessary waveforms. Derive an expression for its output voltage.

5. Discuss the principle of operation of DC-DC step down chopper with suitable waveform. Derive an expression for its average DC output voltage.

6. A step-down 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 r.m.s value of output voltage.

ii) Power delivered to the load .

7. Draw the circuit of CUK regulator and explain its working principle with necessary waveform in detail.

8.A step –up chopper has input voltage of 200V and output voltage of 600V. if the non-conducting time of thyristors chopper is 200ms, compute the pulse width of output voltage . in case pulse width is halved for constant frequency operation, find the new output voltage.

9. Explain the various modes of operation of boost DC-DC converter with necessary waveforms.

10.Explain the working of buck-boost converter with sketch and waveforms and also drive the expression for Is.

11. With neat sketch and output voltage waveforms, explain the working of full bridge SMPS.

12. Explain the operation of BUCK converter in detail.

13. Explain the operation of BOOST converter in detail.

14. Explain the control strategies of chopper.

15. Explain the concept f resonant switching.


UNIT IV INVERTERS PART-A

1. What is meant by inverter?

2. What are the applications of an inverter?

3. What are the main classification of inverter?

4. Why thyristors are not preferred for inverters?

5. Give two advantages of CSI.

6. What is meant a series inverter?

7. What is meant a parallel inverter?

8. What are the applications of a series inverter?

9. What is meant by McMurray inverter?

10. What are the applications of a CSI?

11. What is meant by PWM control?

12. What are the advantages of PWM control?

13. What is VSI?

14.What is CSI?

15. Why thyristors are not preferred for inverters?

16. How the output frequency is varied in the case of an inverters?

17. What are the different methods of forced commutation employed in inverter circuits?

18. What is the main drawback of single phase half bridge inverter?

19. What is the need for voltage control in an inverter?

20. List different methods of controlling the output voltage of inverters.

21. What are the difference types of PWM inverter?

22. What is meant by McMurray inverter?

23. What are the disadvantages of harmonic present in the inverter system?

24. What are the techniques for harmonic reduction?

25. List out the applications of CSI.

26. Difference between VSI and CSI.

27. What are the performance parameters of inverters?

28. What is a PWM inverter?

29. List the advantages of Multiple PWM over single PWM technique.

30. What are the advantages of current source inverter over voltage source inverter?

31. Mention the difference between sinusoidal and modified sinusoidal PWM

techniques.

32. What are the advantages of PWM inverter?

33. Define the term inverter gain?

34. Define modulation index of PWM.

35. List the assumptions that are made in modified McMurray half bridge inverter.

36. What is purpose of connecting diode in antiparallel with thyristors in inverter?

37. What is 60 PWM?

38. What is Space vector PWM?

39. Compare sinusoidal PWM and space vector PWM?40. What are the advantages of SVPWM?

PART B

1. Describe the operation of series inverter with aid of diagrams. Describe an expression for output frequency, current and voltages. What are the disadvantages of basic series inverter?

2. State different methods of voltage control inverters. Describe about PWM

control in inverter.

3. Explain the operation of 3 ф bridge inverter for 180 degree mode of operation

with aid of relevant phase and line voltage waveforms.

4. Explain the working of a single phase full bridge inverter with relevant circuit and waveforms.

5. What is PWM? List the various PWM technique and Explain any one of them.

6. Explain the harmonic reduction by transformer connections and stepped wave inverters.

7. Describe the operation of single phase auto sequential commutated current source inverter with power circuit and waveforms.

8. Explain the operation of 3 ф bridge inverter for 120 degree mode of operation with aid of relevant phase and line voltage waveforms.

9. Describe the different modes of operation of serious resonant inverter unidirectional switch with neat circuit diagram and waveforms.

10. Explain sinusoidal Pulse width modulation technique in detail.

11. Explain Space vector Pulse width modulation technique in detail.

12. Explain the operation of single phase capacitor commutated CSI with R load and necessary waveforms.

13.A single phase full bridge inverter feeds power at 50Hz to RLC load with

R=5 ohms L=0.3H and C=50mF. the DC input voltage is 220V DC. Find i) an expression for load current up to 5th harmonics

ii) Power absorbed by the load and the fundamental power. iii) the RMS and peak currents of each thyristors.

iv) conduction time of thyristors and diodes, if only fundamental components were considered.


UNIT V AC VOLTAGE CONTROLLER PART-A

1. What does ac voltage controller mean?

2. What are the applications of ac voltage controllers?

3. What are the advantages of ac voltage controllers?

4. What are the disadvantages of ac voltage controllers?

5. What are the two methods of control in ac voltage controllers?

6. What is the difference between ON-OFF control and phase control?

7. What is meant by cyclo-converter?

8. What are the two types of cyclo-converters?

9. What is meant by step-up cyclo-converters?

10. What is meant by step-down cyclo-converters?

11. What are the applications of cyclo-converter?

12.What are the effects of load inductance on the performance of ac voltage

controllers?

13. What do you meant by integral cycle control?

14.Write the output R.M.S. voltage for single phase AC voltage controller with resistance load.

15.What is Matrix converter?

16.What are the advantages of Matrix converter?

17.What are the disadvantages of Matrix converter?

18. What are the applications of Matrix converter?

19. Draw the circuit diagram of matrix converter.

20. A step down cycloconverter does not need forced commutation-justify.

PART-B

1. Explain the operation of multistage control of AC voltage controllers with

neat diagram.

2. Explain the operation of 1ф AC voltage controller with RL load.

3. Explain the operation of 1ф sinusoidal AC voltage controller.

4. For a 1 ф 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.

5. Describe three-phase to three phase cycloconverter with relevant circuit

arrangement using 18 thyristors.

6. Explain the principle of single phase to single phase step-down cycloconverter with power circuit and waveforms.

7. Discuss the working of a 3 phase to single phase cycloconverter with neat voltage and current waveforms.

8. Discuss the working of 2 stage sequence control of AC voltage controller.

9.A single-phase full wave AC voltage controllers feeds of R=20 ohms, with an input voltage of 230V,50Hz. Firing angle for both the thyristors is 45˚ calculate

i) R.M.S. value of output voltage. ii) Load power and input p.f.

iii) Average and R.M.S. current of thyristors

10. A six-pulse cycloconverter, fed from 3-phase,400V, 50Hz source, is delivering a load current of 40A to a 1-phase resistive load. The source has an inductance of 1.2mH per phase. Calculate the R.M.S. value of load voltage for firing angle delays of i) 0 and ii) 30˚.