GTU BE 2020 Summer Question Papers || Gujarat Technological University
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GUJARAT TECHNOLOGICAL UNIVERSITY
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BE - SEMESTER- IV EXAMINATION — SUMMER 2020
Subject Code: 3140915
Subject Name: Power Electronics
Time: 10:30 AM TO 01:00 PM
Total Marks: 70
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Date: 04/11/2020
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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| Q.1 | (a) | Explain IGBT with its physical construction diagram and characteristics. | 03 |
| (b) | Draw the SCR static V-I characteristics and explain its behavior in forward conduction, forward blocking and reverse blocking modes. | 04 | |
| (c) | Explain working of 1-f semi converter with the help of voltage and current waveform under resistive load. | 07 | |
| Q.2 | (a) | Compare the RC firing circuit and R firing circuit based on its circuit diagram. | 03 |
| (b) | Describe the effect of high switching frequency on harmonics spectrum in single phase full bridge inverter. | 04 | |
| (c) | Derive the output voltage equation in case of buck and boost converter and draw the comparison. | 07 | |
| OR | |||
| (a) | Draw the circuit diagram of three-phase full converter connected to RL load with continuous conduction. Draw the waveforms of output voltage, output current for firing angle equal to 60°. | 07 | |
| (b) | Write application of cycloconverters. | 03 | |
| (c) | Write advantages and disadvantages of PWM technique to generate gate pulse. | 04 | |
| Q.3 | (a) | Draw necessary waveforms and explain working of single phase full controlled rectifier circuit with R-L load. | 07 |
| OR | |||
| (b) | Justify the statement why SCR is not suitable for dc to ac converter for low power applications. | 03 | |
| (c) | Explain construction of Power MOSFET. | 04 | |
| Q.4 | (a) | Describe the working of a single phase full bridge inverter with relevant circuit and waveforms for R-L Load. | 07 |
| (b) | Derive only expression of RMS output voltage of single phase full wave AC voltage controller with R load. | 03 | |
| (c) | Write important features of sinusoidal pulse width modulation used in PWM inverters. | 04 | |
| Q.4 | (a) | Explain working of 3 phase bridge inverter with star connected resistive load using gate signals, output phase voltage and line voltage. | 07 |
| OR | |||
| (b) | Describe the working of freewheeling diode in Phase controlled rectifier. | 03 | |
| (c) | Write a short note on matrix converter. | 04 | |
| Q.5 | (a) | Explain working of 3 phase bridge inverter with star connected resistive load with 120° mode using gate signals, output phase voltage and line voltage. | 07 |
| (b) | List the various voltage control techniques in DC-DC converters. | 03 | |
| (c) | Give four points of difference between on-off control and phase angle control. | 04 | |
| Q.5 | (a) | Explain the working principal of buck-boost converter with circuit diagram of different modes of operation. | 07 |
| OR | |||
| (b) | Draw the output voltage waveform of three-phase half-wave controlled rectifier with the R-load. | 03 | |
| (c) | State at least two reasons to control or eliminate the harmonics in inverters. List out different techniques to eliminate harmonics in inverter. | 04 | |
| (d) | Explain the parallel operation of SCR. | 07 |
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