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MU Electronics Engineering (Semester 7)
Power Electronics II
December 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) Discuss the effect of source inductance on the performance of a single phase fully controlled converter.
5 M
1 (b) Explain continuous conduction mode and discontinuous conduction mode of class A chopper.
5 M
1 (c) Compare between current source and voltage source inverters
5 M
1 (d) List the advantages offered by the D.C chopper drives over the line commutated converter controlled D.C drives.
5 M

2 (a) Explain sinusoidal pulse width modulation as used in PWM inverters.
10 M
2 (b) A capacitor commutated single phase bridge inverter is operated at 50 Hz with load resistance of 5Ω. Thyristor turn off time is 62μs.
Determine :
1. Commutating capacitor C for successful commutation of SCR.
3. F critical for reliable commutation.
4. R critical.
10 M

3 (a) Draw and explain the operation of single phase capacitor commutated current source inverter with resistive load. Also draw the voltage and current waveforms.
10 M
3 (b) What are the disadvantages of Harmonics present in the inverter circuit. List the methods present in harmonic reduction of inverters and explain any one method in detail.
10 M

4 (a) Draw and explain the operation of a speed control of a D.C series motor by a single phase semiconverter for a continuous motor current. Draw the corresponding voltage and current waveforms.
10 M
4 (b) A D.C shunt motor takes a current of 80A on a 480V supply and runs at 960 Rpm, the armature resistance is 0.25Ω and the field resistance is 120 Ω. A chopper is used to control the speed of the motor in the range of 400 -750 rpm having constant torque. The on period of the chopper is 3ms. The field is supplied directly from 480V supply. Determine the range of frequencies for the chopper.
10 M

5 (a) Explain the operation of induction motor for two different cases when fed with a current source inverter.
(i) Operation at and below rated frequency
(ii) Operation above rated frequency
1 M
5 (b) Exlain the stator voltage control scheme of induction Motor. Also draw and explain the speed ? torque curves.
10 M

6 (a) Describe the operation of On-line UPS system with the help of neat block diagram.
10 M
6 (b) With the help of neat circuit diagram explain the working of SMPS.
10 M

Write a short notes
7 (a) Dual converter
7 M
7 (b) McMurray inverters
7 M
7 (c) Series inverter
7 M

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