Question Paper: Power Electronics II Question Paper - May 2015 - Electronics Engineering (Semester 7) - Mumbai University (MU)
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## Power Electronics II - May 2015

### MU Electronics Engineering (Semester 7)

Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) List the advantages of dc chopper drives over line commutated converter controlled dc drives. 5 marks

1 (b) Explain how semiconverter provides better power factor compared to full converter when both are working as rectifier with RL load. 5 marks

1 (c) What are advantages of flyback converter compared to forward converter? 5 marks

1 (d) Compare between current source and voltage source inverters. 5 marks

2 (a) Draw and explain the operation of speed control of a DC series motor fed by a single phase semiconverter for the continuous motor current. Draw also the associated voltage and current waveforms. 5 marks

2 (b) A 220 V, 1500 rpm, 10 A separately expired dc motor has an armature resistance of 1 ohm. It is fed from a single phase fully controlled bridge rectifier with an ac source voltage of 230, 50Hz. Assuming continuous load current compute:
i) Motor speed at firing angle of 30° and torque of 5 NM.
ii) Developed torque at firing angle of 45° and speed of 1000rpm.
5 marks

3 (a) Explain the operation of dual converter with circulating current. What are the advantages and disadvantages of the same? 5 marks

3 (b) With neat circuit diagram explain the working of load commulated chopper with relevant voltage and current waveforms. Show voltage variation across each pair of SCRs as a function of time. 5 marks

4 (a) Explain the working of McMurry bridge inverter using circuit diagram and appropriate waveforms. 5 marks

4 (b) Explain the operation of Induction Motor for two different cases when fed by current source inverter.
i) Operation at and below rated frequency
ii) Operation above rated frequency.
5 marks

5 (a) Discuss the stator voltage control scheme of induction motor, Also draw and explain the speed torque curves. 5 marks

5 (b) Explain the working of parallel inverter employing feedback diodes. Draw the voltage and current waveforms. What care should be taken to avoid commutation failure. 5 marks

6 (a) Using block diagrams discuss different configurations of UPS. 5 marks

6 (b) Draw and explain the operation of flyback converter with relevant waveforms. 5 marks

7 (a) Effect of source inductance of performance of converter. 5 marks

7 (b) Harmonic reduction in inverters. 5 marks

7 (c) Selection of battery in UPS. 5 marks

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