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USNFourth Semester B.E.DegreeExamnation, JanuarylFebruary 2005

ECffEIBMlMlJEEIITPower Electronics

Page No... 1 EC42

Time: 3 hrs.]Note: 1)Answer anyFIVE full questions.2) Sketch neat diagrams and waveforms.

1. (a) Briefly explain the different types of thyristor power onverters and mentiontwoapplications for each. (10Marks)(b) A transistor chopper circuit is shown in the fig. If aDC supply of 120Voltsis applied and the transistor is switched by applying periodic base pulses ofvoltage varying between 0to1Volt. Sketch the load voltage with reference.tothe input base pulses. Calculate thei) AveragelDC output voltage andii) Average load current assumng the chopper frequency as 200 Hz, dutycycleof operation as 33.33%, and load resistance of IOn. (10Marks)

Vdc

[Max.Marks : 100

LoAD

_ )20V R ::: IO..fLL

2. (a) Explain the important characteristic features of power transistors. With theaidofoutput and transfer characteristics discuss thedifferent operating regionsof apower BJT. (10Marks)(b) A simple transistor switch is used to connect a24 Volt DC supply across arelay coil, which has aDC resistance of 200n. An input pulse of 0to 5Voltamplitude isapplied through aseriesbaseresistor R B at thebasesoastoturnonthe transistor switch. Sketch the devicecurrent waveformwith referenceto the input pulse. Calculatei) Icsii) Value of resistor RB' required toobtain over drive factor of 2,iii) Total power dissipation inthe transistor that occursduring thesaturationstate. (10Marks)

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PageNo... 2 EC42

.LV\ CC

j3 :=525 - ! u /00.V. = = o- 2vat f((So.})U ') = - G~7 Va/!8;:(s;a-,.r

3. (a) What are thyristors? Draw the thyristor symbol and its semconductor struc-ture. Sketch the static anodeV-I characteristics of aunidirectional switchingtriodethyristor deviceand indicate thedifferent regionsonthecharacteristics.Mention the different modesof operation of athyristor. (10Marks)

(b) Explain the different types of turn-on methods (triggering mechanisms) usedto switch ONathyristor device. Usethe two transistor model of athyristoras thebasis toexplain the switching behaviour of the thyristor. (10Marks)

4. (a) Discuss theprocess of thyristor commutation and differentiate between:i) Natural commutation and forcedcommutation.ii) Self commutation and impulse commutation. (10Marks)

(b) A complementary commutation circuit operater fromaDC supply of200Voltsand has resistances R, = R2 = 100, commutating capacitance C = 10pF.Sketch the thyristor voltage waveform for one complete cycleof operation,whenthe twothyristors Tl and T2 inthecircuit aretriggered-periodically oneafter the other. Calculate:i) Peak transient repetitive on state thyristor current that flows, at the

instant of triggering the thyristor deviceandii) Thecircuit turn offtime. (10Marks)

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PageNo... 3 EC42

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Page No... 48. (a) Explain thebasic principle of operation of

i) Singlephase half bridge inverter andii) Singlephase full bridge inverter.With the help of appropriate waveformdisadvantages of each.

EC42

mention the advantages and(10Marks)

(b) Draw the circuit of a single phase, current source inverter employing powerswitching transistors. Sketchthegating signal waveforms and theloadcurrentwaveform Explain the operation of the circuit. (10Marks)

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Page No ... 1 I NEW SCHEME Ir - ~- . - - ~- . - - r - - r - - r - . - - . - .

USN

EE43

Fourth Semester B.E.Degree Examnation, JanuarylFebruary 2005EE I EC I IT I TC I BMI ML

Control SystemsTime: 3hrs.)

Note: Answer any FIVEfull questions.2. All questions carry equal marks.[Max.Marks: 100

1. (a) Distinguish between open loop and closed loop control systems. Giveexamplesfor each. (8 M arks)

(b) The circuit shown in figure (1) (b) is called a lead-lag filter. Find the transferv : (8)function ~ when R1 =1000, R2 =200kO, C1 =1p.F and C2 =O.lp.F(6Marks)

I2-- Q'~ ,----o-

(c) Forthemechanical systemshown in figure (1) (c)write thedifferential equationsof performance and draw themechanical network. (6 M arks)

2. (a) Theblock diagramof afeedback control systemisshown in figure (2)(a). Findi) thetransfer function Y ( s ) I E(s ) wthN =0ii) thetransfer function Y (s ) I N(s ) wth R=0 (8 M arks)

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Page No ... 2 EE43(b) What arethedisadvantages of block diagram representation? (3 M arks)(c) For the signal flow graph shown in fig (2) (c), find the transfer function ~f~using Mason's gain formula. (9Marks)

3. (a) Refer thefigure (3) (a), find thefollowingi) transfer function - } , t : ? andii) e , Wn, %Mp, ts and tp

Take:K =33N/mB=15N-8/mM=3Kg (10 M arks)

\< , c-:r - -~\~~)~;/1 ~f\~@

5(t)

(b) Findtheerror constants Kpl Kv and Ka fortheunity feedbacksystemrepresentedby thefollowing open loop transfer function.

G(8) = 100S2(8+2)(S+5)Determne thesteady state error when the input is r(t) =1+t +2t2. What isthetype and order of thissystem? (10 M arks)

4. (a) Stateand explain Routh - Hurwitz criterion of stability. What areits limtations?(6 M arks)

(b) Determne the number of roots that are (i) in the left half of s-plane, (ii) onthe imaginary axis and (iii) in the right half of s-plane for the systemwith thecharacteristic equation .55 - 84 - 283 +28:1- 88+8=0 (8 M arks)

(c) Anopen loop transfer function has poles at 8= 0,8 = -1and azero at 8= -2.Check therange of K for thestability of theclosed loop system (6 M arks)

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Page No ... 35. (a) Sketch thecomplete root locusof thesystemhaving

G( s )H ( s) = S(S+1)(~2)(S+3)(b) Explain theterms absolute stability and conditional stability.

EE43

(16 M arks)(4M arks)

6. (a) Statetheadvantages of Bodeplots. (2 M arks)(b) Distinguish between gainmargin and phase margin. (4M arks)(c) Plot theBodemagnitude and phase diagrams for theopen loop transfer function

G(s)H(s) = 100(s+2)S(S+4)(s+5)Discuss thestability of theclosed loop system (14M arks)

7. (a) Stateand explain Nyquist stability criterion.(b) UseNyquist stability analysis todetermne thestability range of K if

G(s)H(s) = ~~~~~(6 M arks)

(14M arks)8. (a) Obtaintheopenlooptransfer functionof thecontrol systemwhoseBodemagnitude

plot isshown infigure8(a). (10M arks)

\ '1 . - - - -

(b) Comment on thefollowing statements: (2x5=10 M arks)i) An increase indamping ratio increases therisetime.ii) Unit impulse response of asystemins-domain gives thetransfer function.

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P age N o ... 1 INEW SCHEME IUSN ~~~~~~~~~~~~

EE43

Fourth Semester B.E. Degree Examination, JanuarylFebruary 2005EE I EC I IT I TC I BMI ML

Control SystemsTime: 3 hrs.]

Note: Answer any FIVEfull questions.2. All questions carry equal marks.[Max.Marks : 100

1. (a) Distinguish between open loop and closed loop control systems. Giveexamplesfor each. (8 M arks)(b) The circuit shown in figure (1) (b) is called a lead-lag filter. Find the transferv. (8)function ~ when R1 = icon, R2 =200kn, 01 = IJ.LF and O2 = O.lJ.LF

(6 M arks)

T 2-- r.r.....-------:---------'----o-

(c) Forthemechanical systemshown infigure (1)(c)write thedifferential equationsof performance and draw themechanical network. (6 M arks)

/2. (a) Theblock diagram of afeedback control systemisshown in figure (2)(a). Find

i) thetransfer function Y(s) I E(s) withN =0ii) thetransfer function Y (s) I N(s) with R=0 (8 M arks)

--~--

C o n t d . . . . 2

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Page No ... 2 EE43(b) What are thedisadvantages of block diagram representation? (3 M arks)(c) For the signal flow graph shown in fig (2) (c), find the transfer function ~f~using Mason's gain formula. (9 M arks)

\

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Page No ... 35. (a) Sketch thecomplete root locus of thesystemhaving

G(s)H(s) - K- S(S+1)(S+2)(s+3)(b) Explain theterms absolute stability and conditional stability.

EE43

(16 M arks)(4Marks)

6. (a) Statetheadvantages of Bodeplots. (2Marks)(b) Distinguish between gain margin and phase margin. (4Marks)(c) Plot theBodemagnitude and phase diagrams for theopen loop transfer function

G( s )H ( s) =S(~~i)~~5)Discuss thestability of theclosed loop system (14M arks)

7. (a) Stateand explain Nyquist stability criterion.(b) UseNyquist stability analysis todetermne thestability range of K if

G(s)H (s) =~1~;)(6Marks)

(14M arks)8. (a) Obtain theopenlooptransfer functionof thecontrol systemwhoseBodemagnitude

plot isshown infigure 8(a). (10M arks)

\'1 . - - - -

(b) Comment on thefollowing statements: (2x5=10 M arks)i) An increase indamping ratio increases therisetime.ii) Unit impulse response of asystem ins-domain gives thetransfer function.

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