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Power Electronics Question Paper - Jun 18 - Electrical And Electronics (Semester 5) - Visvesvaraya Technological University (VTU)
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Power Electronics - Jun 18
Electrical And Electronics (Semester 5)
Total marks: 80
Total time: 3 Hours
Note: Answer any FIVE full questions, choosing ONE full question form each module.
1.a.
With neat circuit diagram, input and output wave form , explain the different types of power electronics converters.
(8 marks)
00
1.b.
Discuss the peripheral effects of power electronic equipments.
(4 marks)
00
1.c.
Discuss the major industrial applications of power electronic converter circuits.
(4 marks)
00
OR
2.a.
With the help of neat waveform , explain the reverse recovery characteristics of a power diode. And also obtain an expression for peak reverse current.
(8 marks)
00
2.b.
With the neat circuit diagram and waveforms explain the operation of single-phase full wave rectifier with RL load. Derive the expression for rms output current for continuous load current.
(8 marks)
00
Module-2
3.b.
With neat circuit diagram and switching time explain steady state and switching characteristics of power MOSFET.
(8 marks)
00
3.b.
Give the list of base drive control circuit for BJT. with a neat diagram explain anti-stauration control.
(8 marks)
00
OR
4.a.
With necessary waveforms explain the switching characteristics of an IGBT
(5 marks)
00
4.b.
In the bipolar transistor circuit show in fig Q4(b) $\beta$ varies between 10 to 60. The load resistance Rc = 5$\Omega$ , Vcc= 100V , Vbb= 8V , if Vcₑ(sat)=2.5V and Vbₑ(sat)=1.75V calculate :
(5 marks)
00
i) The value of R₈ that results in saturation with an ODF of 5.
ii) The forced $\beta$ value.
iii) power loss in transistor.
4.c.
Discuss the importance of providing isolation of gate 1 base drive from power circuit and explain the two methods.
(6 marks)
00
Module-3
5.a.
Derive an expression for an anode current of thyristor with the help of two transistor analogy.
(5 marks)
00
5.b.
Write the current diagram and waveform explain the working of UJT triggering technique of SCR.
(5 marks)
00
5.c.
Design the value of di/dt inductor and RG snubber components for an SCR working in a 230V system. Given di/dt rating is 90A/$\mu$s. Effective series resistance is 1.5$\Omega$ and damping factor is 0.6
(6 marks)
00
OR
6.a.
With the help of neat sketch , explain the static V-I characteristics of an SCR. Define latching current , holding current and breakover voltage.
(6 marks)
00
6.b.
Ten thyristor are used in string to with stand a DC voltage of Vs=15kV. The maximum leakage leakage current and recovery charge difference of thyristor are 10mA and 150$\mu$C respectively. Each thyristor has a Voltage sharing resistor of R = 56$\Omega$ and capacitance of C₁=0.5$\mu$F. determine :
(6 marks)
00
i) The maximum steady state voltage.
ii)Steady state voltage derating factor
ii) The maximum transient voltage sharing
iv) The transient voltage derating factor.
6.c.
Explain the V-I characteristics of TRIAC.
(4 marks)
00
Module-4
7.a.
With necessary waveforms, explain the operation of single-phase AC voltage controller with RL load. Derive the expression for rms output voltage.
(8 marks)
00
7.b.
A single phase full wave AC voltage controller has an input voltage of 230V and a load resistance of 10$\Omega$ . The firing angle is 45° Calculate:
(8 marks)
00
i) rms output voltage ii) The output power iii) The input p.f
OR
8.a.
With circuit diagram and waveforms , explain the operation of three phase dual converter.
(8 marks)
00
8.b.
The single phase dual converter is operated form a 129V , 60Hz supply and the load resistance is R= 10$\Omega$. The circulating inductance is Lᵣ= 40mH, delay angle are $\alpha$₁=60° and $\alpha$₂=120º. calculate the peak circulating current and the peak current of converter -1.
(4 marks)
00
8.c.
What are the significance of circulating current in dual converters.
(4 marks)
00
Module-5
9.a.
Classify the different types of choppers the help of circuit and quadrant diagram. Explain the operation of four quadrant chopper.
(8 marks)
00
9.b.
For the chopper circuit shown in Fig 9(b) the duty cycle is 0.t and chopping frequency f=5KHz. Determine:
i)Minimum instantaneous load current
ii)Peak instantaneous load current
iii)Maximum peak- to- peak current in load.
iv) Average and rms load current.
/div>
(8 marks)
00
OR
10.a.
What a neat circuit diagram and waveforms explain 180° mode of operation of a three phase inverter. Give the expression for line and phase voltage for one cycle.
(8 marks)
00
10.b.
Explain sinusoidal pulse width modulation technique of voltage control of single phase inverter.
(4 marks)
00
10.c
Discuss the advantages of the current source inverter over voltage source inverter
(4 marks)
00
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