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APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
FIFTH SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2017
Course Code: EE305
Course Name: POWER ELECTRONICS (EE)

Marks

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Max. Marks: 100 Duration: 3 Hours
Graph sheets will be supplied.
PART A
Answer all questions, each carries 5 marks.

1 Draw the circuit for two transistor analogy of silicon controlled rectifier and

briefly describe the working.
2 Derive the expression for the output voltage of half wave controlled rectifier

with R load.
3 Draw the input and output voltage waveforms of 39 half controlled rectifier with

R load for a firing angle of 30°.

What are the different classifications of inverters?

5 Explain the terms modulation index and frequency modulation ratio related to
pulse width modulation.

6 What are the control strategies for the regulation of output voltage in ac
voltagecontrollers?

7 Explain time ratio control method to vary the output voltage in choppers.

8 Derive an expression for average output voltage in terms of input de voltage and

duty cycle for a step up chopper.

PART B
Answer any twofull questions, each carries10 marks.

9 ಬ Derive the expression for resistance used for static voltage equalisation for a
series connected string.

b) Ina power circuit, 4 SCRs are to be connected in series in a string to handle 6kV
and 1kA. The voltage and current ratings of SCRs are 1800V and 1000A and
have a maximum difference in their blocking currents of 10mA. Difference in
recovery charge is 100. Design ೩ suitable equalizing circuit with figure.

10 A single phase semi converter delivers a constant load current Io . Express its
source current in Fourier Series and derive the expressions for displacement
factor and current distortion factor.

11 ஐ Explain the structure & principle of operation of IGBT.

b) Draw RC triggering circuit for SCR and explain with relevant wave forms.

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