Power Electronics 2018 Question Paper — Government College of Enginee…

The 2018 Power Electronics previous year question paper (Government College of Engineering and Technology, Jammu), with every question and its marks.

Instructions

Attempt five questions in all selecting atleast two questions from each Section.
Assume missing data suitably

Q1. a) Explain different triggering methods of Thyristor. Which one is the most commonly used method and why? (10) b) Explain the block diagram of a typical Power Electronic System. Give advantages and disadvantages of power electronic converters. (10) [20 marks]
Q2. The input voltage $V_s=200\text{V}$ with load resistance of $5\;\Omega$. The load and stray inductances are negligible and the thyristor is operated at a frequency of $f_s=2\text{kHz}$. The required $\text{dv/dt}$ is $100\text{V}/\mu\text{s}$ and the discharge current is to be limited to $100\text{A}$, determine a) values of $R_s$ and $C_s$ b) Snubber loss and c) power rating of snubber resistor. (20) [20 marks]
Q3. Discuss three-phase half-wave controlled converter with circuit diagram and waveforms for different firing angles ($30$, $45$ and $60$ degree) (20) [20 marks]
Q4. What do you mean by Phase-Controlled Rectifiers? Explain the single-phase half-wave controlled converters with the help of circuit diagram and waveforms for RL load with and without free-wheeling diode. (20) [20 marks]

Q5. Explain the various forced commutation techniques for thyristor with the help of circuit diagram and relevant waveforms.(20) [20 marks]
Q6. a) A single phase full wave AC voltage controller has resistive load of $R=10\;\Omega$ and root mean square input voltage is $V_s=120\text{V}$, $60\text{Hz}$. The thyristor is switch on for $n=25$ cycles and is off for $m=75$ cycles. Determine i) rms value of output voltage (10) ii) input power factor and iii) rms current of Thyristors. b) Discuss the principle of working of single-phase to single-phase step down mid-point type Cycloconverter with relevant waveforms and circuit diagram. (10) [20 marks]
Q7. Describe the working of a single-phase half and full bridge voltage source inverter with the help of waveform and circuit diagram.(20) [20 marks]
Q8. a) A step-up chopper has input voltage of $220\text{V}$ and output voltage of $660\text{V}$. If the conducting time of Thyristor-chopper is $100\;\mu\text{s}$, compute the pulse width of output voltage. In case output pulse width is halved for constant frequency operation, find the average value of new output voltage. (10) b) Explain the principle of operation of step-up and step-down chopper. (10) [20 marks]