## November 2, 2011

B.E/B.Tech DEGREE EXAMINATION, NOVEMBER/DECEMBER 2007

Fifth Semester

Electrical and Electronics Engineering

EE 1301 -- POWER ELECTRONICS

(Regulation 2004)
Time: Three hours                                                    Maximum marks: 100
PART A (10 x 2 =20 marks)

1. In Triacs which of the modes the sensitivity of gate is high.
2. Define the term pinch off voltage of MOSFET.
3. Under what conditions a single phase fully controlled converter gets operated as an Inverter.
4. State the principle of phase control in AC-DC converters.
5. Define the term duty cycle in DC-DC converters.
6. What is a DC chopper?
7. Define the term Inverter gain.
8. Differentiate between VSI and CSI.
9. Mention the different types of HVDC link.
10. List the parameters for controlling power in a transmission line.

PART B (5 x 16 = 80)
11 (a) Discuss the transfer, output and switching characteristics of power MOSFEF.
(or)
(b) (b) Explain the switching performance of BJT with relevant waveforms indicating clearly the turn-on, turn-off times and their components. Also define the term SOA.

12.  (a) A two pulse single phase bridge converter is connected to RLE load. Sourse voltage is 230 V, 50 Hz. Average load current of 10 Amps is continuous over the working range. For R = 0.4Ω and L = 2 mH compute.

(i) Firing angle delay for E = 120 V.

(ii) Firing angle delay for E = -120 V.
Indicate which sourse is delivering power to load in parts (i) and (ii).
(or)
(b) For a 1 phase AC voltage controller feeding a resistive load draw the waveforms of sourse voltage gating signals, output voltage, sourse and output current. Describe its working with reference to waveforms drawn. 13 (a) A stepn up chopper has input voltage of 220 V and output voltage of 660 V . If the nonconducting time of thyristor chopper is 100 micro sec compute the pulse width of output voltage. In case the pulse width is halved for constant frequency operation find the new output voltage.
(or)
(b) Classify the basic topologies of switching regulators and explain the operation of buck regulators with continuous load current using suitable waveforms. 14. (a) Describe the working of a 1 phase full bridge inverter supplying R, R.L loads with relevant circuit and waveforms.
(or)
(b) What is the need for controlling the output voltage of inverters? Classify the various techniques adopted to vary te inverter gain and brief on sinusoidal PWM.

15. (a) Describe the principle of operation of no break static ups configuration with a neat block diagram and list out applications.
(or)
(b) Explain the principle of operation of unified power controller as compensator with a neat circuit arrangement.

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