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 Vs=200V with load resistance of R=5?. The load and stray inductance are negligible and the thyristor is operated at frequency of fs=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 Rs and Cs (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 Vs=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)