Download GTU B.Tech 2020 Winter 5th Sem 2150903 Power Electronics I Question Paper

Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 5th Sem 2150903 Power Electronics I Previous Question Paper

Seat No.: ________
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?V (NEW) EXAMINATION ? WINTER 2020
Subject Code:2150903 Date:29/01/2021
Subject Name:Power Electronics ? I
Time:10:30 AM TO 12:30 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.


MARKS
Q.1 (a) Compare SCR with IGBTs.
03

(b) Draw input voltage, output voltage and output current waveform of half wave diode
04
rectifier with RL load.

(c) Develop two transistor analogy model of SCR. Explain working principle of SCR
07
from it.


Q.2 (a) Explain construction of TRIACs.
03

(b) How SCRs can be used as bidirectional switch?
04

(c) Explain series and parallel operation of SCRs and problem associated with them.
07




Q.3 (a) Explain the requirement of gate drive.
03

(b) Explain the term latching current and holding current of SCR. Compare them.
04

(c) Discuss RC triggering circuit. Explain its limitations.
07




Q.4 (a) Explain principle of natural commutation.
03

(b) Explain effect of gate current on V-I characteristics of SCR.
04

(c) With the necessary circuit diagram and waveforms explain the operation of UJT
07
triggering circuit.



Q.5 (a) Explain snubber circuit and its applications.
03

(b) Explain applications of pulse transformer and optocouplers.
04

(c) Sketch circuit diagram and waveform of 3-phase full wave fully controlled converter.
07
Analyse its performance with RL load.



Q.6 (a) Explain requirement of di/dt and dv/dt protection of SCR.
03

(b) Discuss need of freewheeling diode.
04

(c) Sketch circuit diagram and waveform of 1-phase full wave bridge converter. Analyse
07
its performance with RLE load.



Q.7 (a) Compare voltage commutated, current commutated and load commutated chopper.
03

(b) Explain four quadrant operation of DC drives.
04

(c) Explain operation of 3-phase separately excited DC drive controlled by semi
07
converter.



Q.8 (a) Explain working principle of boost converter.
03
(b) Explain four quadrant operation of chopper.
04
(c) Explain the concept of regenerative breaking. Explain chopper controlled DC drive
07
with regenerative breaking.
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