Power Electronics Beu previous year question solution 2021

BIhar engineering university previous year question solution all course all semester. BEU pyq solution 2021 power electronics. BEU pyq solution. Bihar engiineering university pyq solution BEU organizer

1(a). Show that the fundamental r.m.s. value of per-phase output voltage of low- frequency for an m-pulse cycloconverter is given by Vor =Vph(m/pie)sin(x/m)

(b) Shown in figure below the resonant pulse commutation (or class B commu- tation) circuit has C-20 uF and L-5 uH. Initial voltage across capacitor is V₂-230 V. For a constant load current of 300 A, calculate- (i) conduction time for the auxiliary thyristor; (ii) voltage across the main thyristor when it gets commutated; (iii) the circuit turn-off time of the main thyristor.

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2 (a) Explain the I-V characteristics of a thyristor. Label the various voltages, currents and the operation modes.

(b) A 3-phase full-converter delivers a ripple free load current of 10 A with a firing delay of 45°. The input voltage is 3-phase, 400 V, 50 Hz- (i) draw the waveform of source current and write the expression of Fourier series; (ii) calculate input power factor and THD.

3(a) A single-phase full-bridge inverter is connected to a d.c. source Vs. Resolve the output voltage wave shape into Fourier series.

(b) Describe the operation of a single- phase two-pulse mid-point converter with relevant voltage and current waveforms.

4(a) For type-A chopper connected to RLE load, write the basic voltage equations and derive the expression for the maximum and minimum value of load current in terms of source voltage V R, E, T, a and Ta

(b) Hence show that the expression for per unit ripple in the load current of a type-A chopper (Question No. 5(a) is given by

5 (a) A 1-phase full-converter delivers ripple current to RL load with R= 150. The source voltage is 230 V, 50 Hz. For a firing angle of 30°, calculate- (i) rectification efficiency; (ii) voltage ripple factor (iii) THD.

(b) Describe the switching characteristics of power SCR.

6(a) Explain the constructional details and working of n-channel power MOSFET. (B) Describe the switching characteristics of power MOSFETs.

7. With the help of equivalent circuit, obtain the nature of waveform of phase voltage of a star-connected resistive load fed from a three-phase DC to AC bridge-inverter operating in 180° conduction mode.

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8. Discuss the principle of operation of following choppers, with necessary circuit diagram and waveforms: (a) Step-down chopper (b) Step-up chopper Give comments on chopping frequency.