GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER-VI (NEW) EXAMINATION - WINTER 2020
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Subject Code:2160902 Date:27/01/2021Subject Name:Power Electronics — 11
Time:02:00 PM TO 04:00 PM Total Marks: 56
Instructions:
- Attempt any FOUR questions out of EIGHT questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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MARKS
Q.1 (a) Give classification of inverters. Draw circuit diagram of 1-phase half bridge center tapped inverter. [03]
(b) Draw phase voltage and line voltage waveform for 120° conduction of 3-phase H bridge inverter. [04]
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(c) Draw circuit diagram of 3-phase cycloconverter. Comment on output harmonics in the cycloconverter. [07]
Q.2 (a) Define modulation index. What is over modulation region? [03]
(b) Distinguish unipolar and bipolar PWM techniques. [04]
(c) Explain working of line commutated inverters. Give applications of line commutated inverters. [07]
Q.3 (a) Give comparison of AC voltage controller with inverter. [03]
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(b) Determine output harmonics for the ratio fo/fin=15 in sine PWM technique. [04]
(c) Explain effect of non-sinusoidal wave on the performance of rotating AC machine. [07]
Q.4 (a) Compare space vector pulse width modulation (SVPWM) technique with sine PWM (SPWM) technique. [03]
(b) To eliminate 5™ harmonic using selected harmonic elimination' technique, how many variables are to be determined? [04]
(c) Explain sine PWM technique with waveform. How output voltage varies with modulation index? [07]
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Q.5 (a) Distinguish load commutated cycloconverter with line commutated cycloconverter. [03]
(b) Give the reason to keep voltage to frequency ratio constant in induction motor drive. Suggest the converter that can be used for such applications. [04]
(c) Explain the basic principle of matrix converter. Compare it with inverter and cycloconverter. [07]
Q.6 (a) Explain basic principle of cycloconverter. [03]
(b) Justify requirement of gating circuit. Mention its components. [04]
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(c) Explain working of single-phase full wave AC voltage controller connected to R-L load. Derive its equation for the average output voltages. [07]
Q.7 (a) Draw torque speed characteristics of induction motor. Define various region based on the slip value. [03]
(b) Explain working principle of self-controlled synchronous motor drive using cycloconverter. [04]
(c) Explain soft starting of induction motor. Which converter can be used for this purpose? [07]
Q.8 (a) Explain rotor resistance control of induction motor. Suggest the converter that can be used for this application. [03]
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(b) Explain working principle of self-controlled synchronous motor drive using load commutated thyristor inverter. [04]
(c) Explain static Kramer drive. [07]
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