MORE IN Power Electronics II
MU Electronics Engineering (Semester 7)
Power Electronics II
May 2012
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) Explain regenerative braking for D.C motors.
5 M
1 (b) List the merits and demerits of on-line and off-line UPS.
5 M
1 (c) Explain how two quadrant type B chopper operates in first and fourth quadrants.
5 M
1 (d) Compare voltage source and current source inverters.
5 M

2 (a) Draw and explain the operation of single phase semiconverter fed D.C separately excited motor with relevant waveforms and expressions.
10 M
2 (b) Explain with neat diagram the operation of rotor resistance control using chopper.
10 M

3 (a) Explain with neat diagram the working of parallel inverter. Explain the need of feedback diodes. Draw capacitor, SCR and load voltage waveforms.
10 M
3 (b) Describe the principle of step up chopper. Derive an expression for the average output voltage. State the assumptions made.
10 M

4 (a) Explain with relevant circuit diagram the static Scherbius drives for obtaining speeds below and above the synchronous speed.
10 M
4 (b) Explain in detail the operation of dual converter with circulating current. List the advantages and disadvantages of the same.
10 M

5 (a) A 220V, 1500 RPM, 10A separately excited D.C motor has an armature resistance of 0.1 Ω if it is fed from a single phase fully controlled bridge rectifier with an A.C source voltage of 230V, 50 Hz. Assuming continuous load current compute:
i. Motor speed at firing angle of 30oand torque of 30Nm
ii. Developed torque at the firing angle of 45o and speed of 1000 RPM.
10 M
5 (b) Describe a single phase McMurray Bedford method full bridge converter with neat diagram and voltage and current waveforms.
10 M

6 (a) Draw and explain the working of flyback converter with relevant waveforms.
10 M
6 (b) Explain the operation of load commutated chopper with neat circuit diagram and associated current and votage waveforms.
10 M

7 (a) V/f control for induction motor.
7 M
7 (b) Effect of source inductance on performance of converter.
7 M
7 (c) Harmonic reduction in motors.
7 M

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