Power Electronics and Drives - December 2015

MU Instrumentation Engineering (Semester 6)

Total marks: --
Total time: -- INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary 1 (a) Explain SCR characteristics. 5 marks

1 (b) Write advantages of IGBT and MOSFET. 5 marks

1 (c) Explain need of synchronizing circuit in converters. 5 marks

1 (d) Draw the circuit of Jones Chopper and explain the commutation of main SCR. 5 marks

2 Design a converter to give output voltage 150 V at 1A load current. The input is 230V 50 Hz ac supply. Use UJT 2n2646.
V_BBmax=35v for Vbb=16 V, C=0.1μF, η_min=0.56, η_max=0.75, η_type=0.63, Iv=4mA, Ip=25μA Consider temperature compensation. 5 marks

3 (a) With the help of a neat diagram and associated waveform discuss the operation of Buck-Boost converter. Also list the advantages and disadvantages of this type of converter. 5 marks

3 (b) Explain variable frequency I.M. drive. 5 marks

4 (a) Describe the working of 1 phase fully controlled bridge converter in the following two modes.
Rectifying mode
Inversion mode
Also sketch the following waveforms for α=45°, & α=120°. 5 marks

4 (b) Write a short note on reduction of harmonic distortion. 5 marks

4 (c) Briefly explain the V-I characteristics of IGBT. 5 marks

5 (a) Explain the application of power electronics in industrial heating process. 5 marks

5 (b) A 1-phase HW ac regulator feeds power to resistive load of 6Ω from 230V, 50Hz source.
The firing angle of SCR is π/2. Calculate
i) The rms value of output voltage
ii) average input current. 5 marks

6 (a) Explain the current fed ac drives & state its applications. 5 marks

6 (b) State the significant features of traction drives. 5 marks

6 (c) Explain any one type of forced commutation. 5 marks