Power Electronics : Question Paper Jan 2013 - Electronics & Communication (Semester 7) | Visveswaraya Technological University (VTU)

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Power Electronics - Jan 2013

Electronics & Communication (Semester 7)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) What is the power electronics? Give two applications of P.E.(6 marks) 1 (b) What is the difference between thyristor and a TRIAC?(4 marks) 1 (c) What are the peripheral effects of power electronics equipments?(10 marks) 2 (a) What is a bipolar transistor and explain how many types are there and what are their three region operations?(10 marks) 2 (b) What are pinch of voltage, threshold voltage and transconductance of MOSFET?(6 marks) 2 (c) Compare the BJT, MOSFET and IGBTs.(4 marks) 3 (a) What is the difference between SCR and a TRIAC? Explain its characteristics?(8 marks) 3 (b) Q3(b)and Q3(c)
Q3(b) The input voltage of Fig.Q3(b) is V_s=200V with load resistance of R=5?. The load and stray inductance are negligible and the thyristor is operated at frequency of f_s=2 kHz. If the required dv/dt is 100 V/?s and the discharge current is to be the limited to 100 A. Determine (i) the value of R_s and C_s (ii) the snubber loss and (iii) the power rating of snubber resistor.

3(c) What is the common technique for voltage sharing and serial connected thyristor? (8 marks) 4 (a) With a neat diagram and waveforms, explain the principle of single phase full connectors purely resistive load. Determine the expression for voltage o/p voltage and rms o/p voltage.(10 marks) 4 (b) What are the advantages and disadvantages of series conveters?(6 marks) 4 (c) How do you classify phase control converters? Explain.(4 marks) 5 (a) Draw a circuit diagram and associated waveforms, explain the operation of a single phase bi-directional AC voltage controller with resistive load, obtain the rms output voltage.(10 marks) 5 (b) An ac voltage controller in Fig.Q5(b) has a resistive load of R=10? and the root-mean-square (rms) input voltage is V_s=120V, 60Hz. The thyristor switch is on for n=25 cycles and is off m=75 cycles. Determine (i) the rms output voltage V₀, (ii) the input power factor (PF) and (iii) the average and rms current of thyristors.

(7 marks) 5 (c) What are the advantages and disadvantages of ON-OFF control?(3 marks) 6 (a) What is an inverter? Explain its principle of operation (any one) with a neat diagram and waveforms.(8 marks) 6 (b) What are the performance parameter of inverters?(6 marks) 6 (c) How to differentiate 1? and 3? inverters?(6 marks) 7 (a) What is the principle of stepdown operation of chopper?(4 marks) 7 (b) The stepdown chopper circuit shown in Fig.Q7(b)(i) & (ii), having resistive load. Derive an expression for the following:
(i) Average output voltage V₀(av)

(ii) rms output voltage V₀ (rms). (8 marks) 7 (c) A chopper circuit is operating on TRC at a frequency of 2 kHz on a 460 V supply of the load voltage of 350 V. Calculate the conduction period of the thyristor in each cycle.(8 marks)

Write short notes on:

8 (a) Communication techniques(5 marks) 8 (b) Difference between ON-OFF control and phase control(5 marks) 8 (c) Static induction transistor (SIT's)(5 marks) 8 (d) Performance parameters of rectifier.(5 marks)

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