Power Electronic and Drives

E

Effective Date: 01 Dec

SUBJECT SUBJECT LEVEL TIME / DU DATE

1. Plea 2. This

3. Plea

4. Answ illus 5. This ques 6. Answ 7. Fom

cember 2008

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INSTRUCTION: Answer ALL questions.

Please use the answer booklet provided.

Question 1

(a) List four types of power electronics conversion in energy power converter.

(4 marks) (b) Draw single-phase bridge rectifier with resistive load circuits and explain the

operation.

(6 marks)

(c ) Explain briefly the difference conversion of static applications and drive applications in power electronic system and state two examples each of them.

(10 marks)

Question 2

(a) Draw a single-phase inverter with resistive load, sketch the output voltage and explain the operation.

(10 marks)

(b) Prove that the DC output voltage (VDC) of a single phase half-wave uncontrolled rectifier with resistive load is

π

m DC

V

=

V

^.

dt t T V

V

T

m

DC 1 ² sin( )

0



ω

=

(10 marks)

Question 3

(a) Name and draw three types of DC to DC power converter.

(6 marks)

(b) Name the type of converter in Figure 1 and explain the operation when S is on and off.

(6 marks)

Figure 1

(c) (i) Explain the concepts of unidirectional and bidirectional controllers for AC voltage controllers.

(4 marks)

(ii) Explain the principles of On-Off Control for AC voltage controller in Figure 2 and sketch the output voltage.

(4 marks)

Figure 2

INSTRUCTION: Answer TWO (2) questions only Please use the answer booklet provided.

Question 4

(a) Figure 3 is the boost converter which has parameter supply voltage (Vs) = 24 V, duty cycle (D) = 0.7, load resistance (R_L) = 10 Ω, inductor (L) = 14 µH, capacitor (C)

= 60µF and the switching frequency is 200KHz. Determine, i. The output voltage Vo

ii. the average, maximum and minimum inductor current (IL, Imax and Imin) iii. the output voltage rippled (

Vo

Δ

Vo

₎ iv. the average output current I0

Figure 3

(20 marks)

Question 5

A single-phase half-wave controlled rectifier is connected to 120Vrms, 50 Hz source. The output of the rectifier is connected to a 10 ohm resistive load. If the average output voltage is 80% of the maximum possible output voltage, determine:

(a) the delay angle α

(b) the rms and average output voltage (c) the average and rms thyristor current (d) the input power factor

Question 6

The AC voltage controller in Figure 4 is connected to a resistive load R = 30 Ω and the input supply voltage Vs = 240 V (rms), 50 Hz. The delay angles of thyristorT1 and T2 are equal:

1 2 =90⁰. Calculate (i) the rms output voltage (ii) the input power factor (PF)

(iii) the average and rms thyristor current (IA and IR)

(20 marks)

Figure 4

END OF QUESTION PAPER

Performance Parameters of Rectifiers Formula 1.

P

DC

= I

DC

V

DC

2.

P

_AC

= I

_RMS

V

_RMS

3.

AC DC

P

=

P η

4.

V

AC = {

V

²RMS −

V

²DC) 5.

DC RMS

V FF

=

V

6.

DC AC

V RF

=

V

7.

S S

DC

V I TUF

=

P

8. ^DF =^Cosϕ

9.

2 1

2 1

2 1 2











 −

=

S S S

I I HF I

10.

S PEAK S

I CF = I ^{( )}

11.

^COS ϕ

VI P P

PF P

RMS

REAL = =

= ⁰

Trigonometro Function

n nxdx

cos

nx

sin =−



Single phase half-wave controlled rectifier:

n = ^dc =^0.5

(

¹+^cos

α )

V

V V

,

V

_m = 2×

Vs

,

( α )

π

^{1 cos}

2 +

= ^m

dc

V V

12

2 2 sin 1

2 

 



 



 



 − +

= π α α

π

m rms

V V , Pf = Po/VA

Single phase full-wave controlled rectifier:

dm dc

n V

V =V ^,

V

_m = 2*

Vs

^,

^V

^{dc =}

^V _π

^m

(

^1+cos

^α )

π α π

α

4

) 2 sin(

2 2

1− +

= m rms

V

V

, Pf = Po/S where, S = Vsrms x Irms

Boost converter Vo = Vs / (1- D),

R D I

_L

V

^S ₂

) 1 ( −

= ^,

L DT V R D

I V

^{S S}

) 2 1

( ²

max +

= − ^,

L DT V R D

I V

^{S S}

) 2 1

( ²

min −

= −

I0 = V0 / R,

8 2

1 LCf

D V

V

o

o = −

Δ

AC voltage controller

2 1

2 2 sin

1 

 



 



 



 − +

= π α α

π

s

o V

V , P_o=V_sI₀^, (cos 1) 2

2 +

= α

π^R I_A V^s

12

2 2 ( sin

1

2 

 − +

=

π α α

π

R

I

_R

V

^s