GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VI (New) EXAMINATION - WINTER 2019
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Subject Code: 2160902 Date: 09/12/2019Subject Name: Power Electronics — I1
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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MARKS
Q.1 (a) Define total harmonic distortion. What is the importance of THD while designing an inverter? 03
(b) Write important features of sinusoidal pulse width modulation used in PWM inverters. 04
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(c) Mention disadvantages of harmonics produced by an inverter. What are the different methods to reduce harmonic content? Explain any one harmonics reduction technique in detail. 07
Q.2 (a) Compare VSI and CSI 03
(b) Write advantages and disadvantages of PWM technique to generate gate pulse. 04
(c) Discuss the principle of working of a three-phase bridge inverter with an appropriate circuit diagram. Draw gate signal, phase voltage and line voltage waveforms for 120° conduction of SCRs with star connected resistive load. 07
OR
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(c) A full bridge inverter is operated from a dc supply of 280V and in unipolar PWM mode. Determine (1) Fundamental output voltage at M=0:8 and (2) First five dominant harmonic order if M= 24. 07
Q.3 (a) Derive only expression of RMS output voltage of single phase full wave AC regulators with R-load. 03
(b) Explain integral cycle control and phase control method. 04
(c) A single phase AC regulator with R-L load has input voltage 230V, 50 Hz. R=4O and ?L=3O. Calculate the control range of firing angle, maximum power and power factor. 07
OR
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Q.3 (a) Write application of Cycloconverters. 03
(b) Write advantages of AC voltage regulators using either Triac or Thyristors. Mention at least one limitation of it. 04
(c) Write importance of sequence control in AC regulators. Explain two stage sequence control AC regulators with circuit diagram and waveforms. 07
Q.4 (a) Compare Cycloconverter with DC link converter. 03
(b) Write shortly Load-commutated cycloconverter. 04
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(c) Describe single phase Cycloconverter with centre-tapped transformer configuration with neat circuit diagram and plot input and output voltage waveform for R-load and frequency of 16.66 Hz. 07
Q.4 (a) Explain briefly slip-power recovery scheme. 03
(b) Explain effect of non-sinusoidal waveform on performance of AC machine. 04
(c) Write short technical note on matrix converter. 07
Q.5 (a) Compare AC drives and DC drives. 03
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(b) Explain rotor resistance control of induction motor drives. 04
(c) Explain the method of controlling induction motors using Cycloconverters. 07
OR
Q.5 (a) Why voltage to frequency ratio kept constant in Induction Motor Drives. 03
(b) Briefly explain self controlled synchronous motor drive using electronic commutator. 04
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(c) List out types of synchronous motors. Explain Motoring and Regeneration region of Cylindrical rotor synchronous motor by plotting torque vs. d 07
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