 Power Electronics | Nagpur University | Summer-2019 - Grad Plus

# Power Electronics | Nagpur University | Summer-2019

## Power Electronics

NRT/KS/19/3476
Time : Three Hours
Max. Marks : 80
_____________________________________________________________________
Notes : 1. All questions carry marks as indicated.
2. Solve Question 1 OR Questions No. 2.
3. Solve Question 3 OR Questions No. 4.
4. Solve Question 5 OR Questions No. 6.
5. Solve Question 7 OR Questions No. 8.
6. Solve Question 9 OR Questions No. 10.
7. Solve Question 11 OR Questions No. 12.
8. Due credit will be given to neatness and adequate dimensions.
9. Assume suitable data whenever necessary.
10. Illustrate your answers whenever necessary with the help of neat sketches.
11. Use of non programmable calculator is permitted.

1. a) Draw and explain V-I characteristics of SCR, Describe all operation regions and define latching and holding current.  [07 M]

b) Describe Auxiliary commutation method of SCR with circuit diagram. [06 M]

OR

2. a) Draw and explain two transistor analogy of SCR with expression of anode current. [07 M]

b) Enlist the various commutation methods of SCR and explain complimentary commutation in detail.  [06 M]

3. a) Draw relaxation oscillator circuit using UJT for generating triggering to SCR also explain operation.  [07 M]

b) Draw and explain output characteristics of power MOSFET. [06 M]

OR

4. a) Design a UJT as a relaxation oscillator using UJT2M2646 with following specification also determine R1, R2, Rmin, Rmax  and the limits of output frequency.
η=0.7, Ip=50μA, VV=2 V , IV=6 mA, VBB=20 V, RBB=7kΩ,  Ie0=2mA
Assume C = 0.1 μF .  [07 M]

b) Describe four modes of Triac in detail. [06 M]

5. a) Describe the operation of 3 phase six pulse bridge converter with resistive load, draw relevant waveform for firing angle α = 30º.  [08 M]

b) Explain the effect of Freewheeling Diode on the performance of converter with R-L load.  [06 M]

OR

6. a) Describe the operation of 2 pulse mid point converter with R-L load also draw relevant waveform for α = 30º.    [07 M]

b) Explain the effect of battery load on the performance of single phase fully controlled bridge converter. [07 M]

7. a) Draw circulatory of single phase to single phase cycloconverter obtaining O/P frequency equal to 1/3 of input frequency with relevant waveform. [07 M]

b) Write a short note on power factor improvement methods. [07 M]

OR

8. a) Draw and explain dual – converter and prove that
α1 + α2 =180º . [07 M]

b) Explain the speed control SEDC Motor using line commutated converter. [07 M]

9. a) Draw and explain the operation of step-up chopper also derive the expression of output voltage.  [08 M]

b) Describe the operation of two quadrant chopper (Class C) in detail. [06 M]

OR

10. a) Explain the operation of basic series inverter, also Enlist the various drawbacks. [08 M]

b) A step-up chopper is used to deliver a load voltage of 500 Volt from 200 Volt D.C. source. If the blocking period of SCR is 80 μ sec. Calculate the required pulse width.  [06 M]

11. a) Explain 3Φ bridge inverter operation for 180º mode of operation with relevant phase voltage waveform.  [07 M]

b) Distinguish between voltage source and current source inverter. [06 M]

OR

12. a) Enlist the different output voltage control techniques of Inverter, Explain any one detail. [07 M]

b) Describe the various applications of current source inverter. [06 M]

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