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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
ME SEMESTER I EXAMINATION SUMMER 2017
Subject Code: 2710702 Date:10/05/2017
Subject Name: Power Electronics
Time: 02:30 pm to 05:00 pm Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

Discuss static and dynamic characteristics of power MOSFET and IGBT.
07

Draw the circuit diagram of buck-boost converter and explain the continuous conduction mode of operation with necessary waveform and equation.
07
Q.2

With neat circuit diagram and waveforms, explain the working of Flyback converter. Derive output voltage in terms of duty ratio.
07

Explain the working of cuk converter with neat diagram and necessary waveform. Derive the expression for output voltage.
07
OR

With neat circuit diagram and waveforms, explain the working of practical forward converter. Derive output voltage in terms of duty ratio.
07
Q.3

Explain unipolar modulation scheme for H-bridge inverter operation. How is it different from bi-polar modulation? What is the effect of unipolar schemes on the output voltage's harmonic spectrum?
07

Draw space vector diagram for 3-phase voltage source inverter. Explain the control of inverter using space vector modulation.
07
OR
Q.3

Explain the working of Auto-Sequential Commutated Current Source Inverter with neat diagram, necessary waveforms.
07

Explain various harmonic reduction techniques used in inverter.
07
Q.4

How design of magnetic components used in power electronic circuit is different than when used in normal electric circuits? Explain 'Area of Product' method in brief.
07
Draw the neat circuit diagram of three phase full wave AC voltage controller and explain it's working with wave forms for firing angles α=60°.
07
OR
Q.4
Explain the working of 3-phase to 3-phase cyclo-converter with necessary circuit and waveforms.
07
Classify A.C. voltage controller explain principle of ON-OFF control Phase angle control.
07
Q.5

Describe the necessity of Isolation of gate and base drives and explain how they are implemented using the pulse transformer and optoisolator with necessary circuit diagrams.
07

Draw power circuit for a three phase full converter feeding RLE load. Draw output voltage waveforms for a firing angle delay of 60° indicating the conduction of its various elements on the assumption of continuous output current. Hence, obtain an expression for the average output voltage in terms of α.
07
OR
2
Q.5
Explain how two three phase full converters can be connected back to back to form a circulating current type of dual converter. Discuss its operation with the help of voltage waveform across each converter load and reactor.
07

Explain the effect of source inductance for single phase full converter. Also derive the equation of output voltage V0 in terms of firing angle α and source inductance LS.
07