Anna University Model Question Paper BE VI sem E&I POWER ELECTRONICS







Time: 3hrs                                                                                                Max. Marks: 100

Answer all Questions

PART – A (10 x 2 = 20 Marks)


  1. Give the difference between a triac and IGBT.


  1. Compute the peak inverse voltage of thyristor connected in the three phase six pulse bridge circuit having input voltage of 415V. Voltage safety factor is 2.1.


  1. Define string efficiency.


  1. What are the basic requirements for triggering the SCR?


  1. What are the effects of adding a free wheeling diode to a single phase fully controlled converter feeding R-L load?


  1. Mention the advantage and disadvantage of circulating current scheme in a dual converter.


  1. How will you choose the value of L & C in a series inverter?


  1. What is the control strategies employed in DC choppers?


  1. Why the DC drives systems unsuitable for energy saving applications of pumps or fans?


  1. List down the basic circuit configurations of SMPS?


PART – B (5 x 16 = 80 Marks)


11.i)     With the help of two transistor analogy, explain how an SCR turns ‘ON’ once a gate pulse is applied.


 ii)     Discuss the construction of an IGBT. With the help of its V-I characteristics, describe its working.


12.a)    Describe in detail any three forced commutation methods.




12.b)    Explain the principles of resistance firing circuit and resistance capacitance firing circuit.


13.a)    A single-phase fully controlled bridge converter supplies an inductive load. Assuming that the output current is virtually constant and is equal to Id. Determine the following performance measures if the supply voltage is 230V and if the firing angle is maintained at π/6 radians. (i) Average output voltage (ii) Supply RMS current (iii) Supply fundamental RMS current (iv) fundamental power factor (v) supply power factor (vi) supply harmonic factor (vii) voltage ripple factor.




13.b)    Explain the basic principle of operation of a cyclo converter with a neat equivalent circuit diagram. Also draw and discuss the wave forms illustrating the operation of the idealized cyclo converter circuit with loads of various displacements angle.


14.a)    Single phase full bridge inverter has a resistive load of R = 3 ohm the DC input voltage Edc = 50V. Compute (i) The RMS voltage at the fundamental frequency (ii) the output power (iii) the average and peak current of each thyristor (iv) the peak reverse blocking voltage of thyristor.


Table of Contents



14.b)    Describe the working of step-up chopper with suitable waveform. Also derive an expression for its average output voltage.


15.a)    Describe the need and function of single phase AC voltage regulator.




15.b)    Explain in detail closed loop control of DC motor drives.




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