EE2301 Power Electronics Question Bank : valliammai.co.in
Name of the College : Valliammai Engineering College
Subject : Power Electronics
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Document Type : Question Bank
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Valliammai Power Electronics Question Paper
POWER SEMI-CONDUCTOR DEVICES
PART-A
Unit – I
1. Draw the V-I characteristics of SCR and mark the holding current and latching current in the characteristics.
2. What are the advantages of GTO over BJT?
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3. Define: holding current and latching current of SCR
4. Define: string efficiency of SCRs connected in series
5. IGBT is a voltage controlled device. Why
6. Distinguish between holding current and latching current of SCR.
7. Why is pulse triggering preferred over RC triggering?
8. What is reverse recovery time?
9. Mention any two advantages of advantages of GTO over SCR
10. Why MOSFETs are not preferred for low frequency applications?
11. Why are IGBT becoming popular in their application to controlled converters?
12. What are the factors that influence the turn-off time of a thyristor?
13. Draw the turn on characteristics of SCR and mark the timings td ,tr and ton.
14. In TRIAC which of the modes the sensitivity of gate is high.
15. Define the term pinch off voltage of MOSFET
16. What are the advantages of MOSFET with BJT?
17. Power MOSFET is a voltage controlled device. Why?
18. Power BJT is a current controlled device. Why?
19. What is a snubber circuit?
20. Define hard-driving or over-driving.
PART B
1. Explain the structure and operation of turn on and turn of characteristics of SCR.
2. (i) Describe the any two methods of turn-on mechanism of SCR.
(ii) Explain the turn off characteristics of SCR.
3. Discuss the transfer, output and switching characteristics of IGBT
4. Explain the switching performance of BJT with relevant waveforms indicating clearly the turn on, turn off times and their components.
5. (i) Draw and explain the forward characteristics of SCR using two transistor model of SCR.
(ii) Compare any six salient features of MOSFET with IGBT
6. (i) Compare the performance characteristics of MOSFET with BJT.
(ii) Briefly discuss the R-C triggering of SCR.
7. Discuss the operation of power MOSFET and explain the transfer, output and switching characteristics of power MOSFET
8. Differentiate natural commutation and forced commutation.
9. Explain the operation of driver and snubber circuits for power MOSFET.
10. Explain with diagram the various modes of working of TRIAC
UNIT-II
PHASE-CONTROLLED CONVERTERS
PART – A
1. What is two pulse converters?
2. What is full converter? Mention its uses.
3. What is a delay angle of converters?
4. What is the principle of phase control half wave rectifier?
5. What is the function of freewheeling diode in Semi converter?
6. Draw the three phase half wave converter.
7. Write the expression for 3F full converter with RL load.
8. What is meant by full controlled rectifier?
9. Define: firing angle a 10. List the merits of phase control.
11. Why the power factor of semiconverter better than full Converter?
12. What is the inversion mode of rectifiers?
13. Define the terms: displacement factor, total harmonic distortion.
14. Under what conditions a single phase fully controlled converter gets operated as an inverter.
15. State the principle of phase control in AC-DC converter
16. It is required to operate a single phase full converter in the inverter mode with RLE load. Should the average output voltage be more or less than E during inverter operation? Why?
17. List various applications of phase controlled converters.
18. What is freewheeling diode and what is the purpose?
19. Define displacement factor.
20. Is the input power factor of fully controlled converter is less than that of half controlled converter? Justify your answer
PART B
1. Discuss the operation of single phase half controlled rectifier with R load. Also derive the average output voltage equation.
2. Explain the operation of three phase half controlled rectifier supplying R load with neat sketch. Also derive an expression for the average output voltage.
3. With necessary circuit and waveforms, explain the principle of operation of three phase fully controlled bridge rectifier feeding R-L load and drive the expression for the average output voltage.
4. With necessary circuit and waveforms, explain the principle of operation of single phase ac voltage controller feeding R load by on-off control and phase control. Derive the expression for rms value of output voltage in both cases.
5. For the single phase fully controlled bridge is connected to RLE load. The source voltage is 230 V, 50 Hz. The average load current of 10A continuous over the working range. For R= 0.4 O and L = 2mH, Compute (a) firing angle for E = 120V (b) firing angle for E = -120V
6. For a single phase Ac voltage controller feeding a R load draw the waveforms of source voltage, output voltage, source and output current. Describe its working with reference to waveforms drawn.
7. i) Describe the operation of single phase two pulse bridge converter using 4 SCRs with relevant waveforms.
ii) Discuss the working of the above converter mode with RLE load.
8. i) A single phase two pulse converter feeds power to RLE load with R= 6O, L= 6mH, E= 60V, AC source voltage is 230V, 50Hz for continuous condition. Find the average value of load current for a firing angle of 50?. In case one of the 4 SCRs gets open circuited. Find the new value of average load current assuming the output current as continuous.
ii) Draw the possible configurations of a single phase AC voltage controller and compare them.
9. Discuss with the aid of schematic diagram and waveforms, the principle of operation of a two quadrant two pulse converter in the rectifying and inverting mode of operation.
10. Draw the circuit diagram and explain the operation of three pulse half controlled rectifier.
11. Draw the power circuit diagram of a 6 pulse two quadrant converter circuit. Explain the operation of the circuit with necessary wave forms.