Bihar engineering university previous year question solution . Power electronics question paper solution is provided. Solution is easy to understand and it will help in your examination. Go through the BEU PYQ to excel in your exam
Q.1 Choose the correct option of the following (Any seven question only):
(a) In a 3-phase full-wave a.c. to d.c. converter, the ration of output-ripple frequency to the supply-voltage frequency is
(i) 2
(ii) 3
(iii) 6
(iv) 12
b) Reverse recovery current in a diode depends upon
(i) forward field current
(ii) storage charge
(iii) temperature
(iv) PIV
(c) The most suitable device for high frequency inversion in SMPS is
(i) BJT
(ii) IGBT
(iii) MOSFET
(iv) GTO
(d) As compared to power MOSFET, a BJT has
(i) lower switching losses but higher conduction loss
(ii) higher switching losses and higher conduction loss
(iii) higher switching losses but lower conduction loss
(iv) lower switching losses and lower conduction loss
(e) In a thyristor-controlled rectifier, the firing angle of thyristor is to be controlled in the range of
(i) 0° to 90°
(ii) 0° to 180°
(iii) 90° to 180°
(iv) 90° to 270°
(f) A single-phase voltage source square-wave inverter feeds pure inductive load. The waveform of the load current will be
(i) triangular
(ii) rectangular
(iii) trapezoidal
(iv) sinusoidal
(g) An SCR is a
(i) four layer, four junction device
(ii) four layer, three junction device
(iii) four layer, two junction device
(iv) three layer, single junction device
(h) In a step down chopper, if V₁ = 100 V and the chopper is operated at a duty cycle of 75%. Find the output voltage.
(i) 100 V
(ii) 25 V
(iii) 75 V
(iv) None of the above
(i) The single phase mid-point type cycloconverter uses number of SCRS
(i) 2
(ii) 4
(iii) 5
(iv) 8
(j) The principle of three phase cycloconverter is to
(i) add and remove number of SCRS
(ii) vary progressively the firing angle of the devices
(iii) keep the firing angle as 0º for all the devices
(iv) none of the mentioned
ALL IN ONE PDF SOLUTION PROVIDED BELOW
Q.2 (a) A 3-phase bridge inverter delivers power to a resistive load from a 450 V d.c. source. For a star connected load 10 2 per phase, determine the following for 120° mode of operation:
(i) r.m.s value of output phase and line voltages
(ii)r.m.s value of load current
(iii) Load power
(b) Describe the structural features of power diodes. How do these differ from signal diodes?
Q.4 (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.
Q.5 (a) Explain the time ratio control and current limit control of DC choppers.
(b) For an SCR, gate-cathode characteristic is given by V1+101g. Gate source voltage is a rectangular pulse of 15 V with 20µ sec duration. For an average gate power dissipation of 0.3 W and a peak gate-drive power of 5 W, compute:
(i) the resistance to be connected in series with the SCR gate
(ii) the triggering frequency
(iii) the duty cycle of the triggering pulse.
Q.6 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 120° conduction time.
Q.7 (a) For type A chopper connected to RLE load, write the basic voltage equation and derive the expression for the maximum and minimum value of load current in terms of source voltage V., R, E, T, a, T
(b) A type-A chopper feeds RLE load. For low values of lon, limit of continuous conduction is reached when load current during TON <t<T fall to zero. Derive an expression for this load current from basic voltage equations and hence obtain waveform that the duty cycle a’ at the limit of continuous conduction is given by
Q.8 (a) A single phase ac voltage controller is employed for controlling the power flow from 230 V, 50 Hz source in to a load circuit consisting of R = 42 and L = 3 2. Calculate (i) the control range of Firing angle; (ii) the maximum power delivered to load and power factor; (iii) the maximum values of average and rms SCR currents.
(b) Describe the operation of single phase full wave ac regulator feeding resistive load. Derive the expression for output voltage.
Q.9 Write short notes on any two of the following: (i) Boost convertor (ii) Cycloconverters (iii) Firing circuits for thyristors
(iv) Thyristor commutation techniques
BEU POWER ELECTRONICS 2021 SOLUTION = DOWNLOAD
BEU POWER ELECTRONICS 2020 SOLUTION = DOWNLOAD
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