Power Electronics-1 - May 2015
Electronics Engineering (Semester 6)
TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) Draw and explain V-1 characteristics of SCR.(5 marks) 1 (b) What is the need of frewheeling diode in controlled rectifier. Explain with example.(5 marks) 1 (c) What do you understand by di/dt and dv/dt rating of SCR.(5 marks) 1 (d) Explain the principle step down chopper. State load voltage equation.(5 marks) 2 (a) Explain half controlled rectifier using SCR. Draw waveform and derive the relation for output load voltage.(10 marks) 2 (b) Draw and explain single phase full bridge inverter. Draw waveforms.(10 marks) 3 Single phase half bridge inverter has a resistive load of 3 Ω and the DC input voltage Edc=50 V. Calculate
i) RMS output voltage at the fundamental frequency
ii) Output power P0.
iii) The average and peak current of each thyristor.
iv) The peak reverse blocking voltage of each thyristor.(20 marks) 4 (a) Explain the working of single phase to single phase cycloconverter with purely resistive load. Draw circuit diagram and waveforms.(10 marks) 4 (b) The input voltage to the buck-boost converter is Edc=14 V. The duty cycle a= 0.6 and the switching frequency is 25 Khz. The inductance L=180 μH and filter capacitance C=220 μH. The average load current Io=1.5 A. Calculate
i) The average o/p voltage E0
ii) The peak-to-peak output voltage ripples ΔVc.
iii) The peak-to-peak current of inductor Δ I
iv) The peak current of the device Ip.(10 marks) 5 (a) Explain circuit diagram and working of three phase inverter 1807deg; conduction, mode with resistive load.(10 marks) 5 (b) Differentiate between symmetrical and asymmetrical IGBT.(5 marks) 5 (c) Draw and explain switching characteristics of IGBT.(5 marks) 6 (a) Explain the voltage control technique in inverter using sinusoidal pwn method.(10 marks) 6 (b) Draw and explain dual converter with all four quadrants of operation.(5 marks) 6 (c) Define forced communication. Explain Class D communication with respect to circuit diagram. Working and waveforms.(5 marks)