*EJM150*

EJM – 150

I Semester M.E. (PE) Degree Examination, March 2013 (2K8 Scheme) PE 111 : POWER ELECTRONIC CONVERTERS (PE/PES) Time : 3 Hours

Max. Marks : 100

Instruction : Answer any five full questions. 1. a) With a neat sketch and waveform explain the operation of three phase semi converter. For α = 60° for highly inductive load. Derive Vo avg and Vo rms equations. 12 b) Explain symmetrical angle control technique with sketch.

8

2. a) What is overlap angle ? Derive an equation for the overlap angle.

12

b) A three phase transformer having leakage inductance of 2 mH/phase is connected to three phase full wave bridge rectifier circuit with a balanced sinusoidal voltage of 230 V/phase, 50Hz. The load current on DC side is 15 Amps.

8

i) Obtain the drop in the DC output voltage caused by the internal reactance drop. ii) Calculate the firing angle required for the SCRS when the DC output voltage is 200 V. H ,calculate the overlap angle for the phase iii) Using the condition stated in O currents.

3. With a neat sketch and waveform explain the operation of three phase bidirectional delta connected controller for α =120°. Derive expression for the output voltage. 20 4. a) What is cyclo converter ? Explain single phase operation with sketch.

8

b) Explain the operation of stepdown chopper with RL load. Derive equation for ripple current in continuous current mode. Draw the relevant circuit and waveforms. 12 P.T.O.

*EJM150*

EJM – 150

5. a) What is an impulse commutated chopper ? Derive equation for circuit turn off time. 10 b) A single phase bridge inverter has a resistive load of R = 2.4 Ω and the DC input voltage is Vs = 48 V. Determine. i) the rms output voltage at the fundamental frequency Vo1. ii) the output power Po iii) the average and peak currents of each transistor iv) the peak reverse blocking voltage VBR of each transister v) the THD vi) the DF vii) the HF and DF of the LOH.

10

6. Explain with sketch the operation of a three phase inverter operating in 180° conduction mode. Obtain an expression for line to line voltage.

20

7. Write short notes on the following : i) current source inverter ii) four quadrant chopper iii) circulating current in dual converter iv) modulation index M.

(5×4=20) ______________