EE 4303 – POWER ELECTRONICS DECEMBER 1, 2008
Second Sessional Examination Time Allowed: 1.0 hour
Note: The Exam consists of two problems. Read the statements carefully and schedule your
time according to the points assigned to the problems.
Problem 1: {3+2+5+4+3+2+6=25 marks}
Consider the full-wave rectifier circuit shown in the attached figure. The 50H inductors are
representing line inductance due to transformer leakage and cables. The converter is
operating with a firing delay angle
45
. Determine:
a. The average output voltage o
vwith zero line
inductance;
b. The load current value in amperes;
c. The commutation interval in s;
d. Plot the output voltage, o
vwith 50H line
inductance;
e. Determine the new value of average output
voltage o
vwith 50H line inductance;
f. Determine the output power
g. Accurately plot the current through the two thyristors.
Problem 2 {25 marks}
For a three-phase full-bridge rectifier using six thyristors, the input voltages are specified as
tva
cos100,
120cos100 tvb
and
120cos100 tva
a. Determine the firing sequence of the thyristors ………………………………….. 3
b. For a firing delay angle =30o, plot gate pulses for thyristor T1, ……………….. 2
c. Plot the current through T4, ……………………………………………………… 2
d. Plot the voltage across T4, ……………………………………………………….. 3
e. Plot the output voltage, ……………………………………………………………2
f. Plot the voltage across 100mH load inductor ……………………………………..1
g. Determine the peak and average current in T4 ……………………………………4
h. Determine the rms value of line current …………………………………………..3
i. Determine the real input power (Watts) ………………………………………….. 2
j. Determine the apparent input power (VA) ………………………………………..2
k. Determine the power factor ……………………………………………………….1
vo
V1=220VRMS
100 mH
2 ohm
V2=220VRMS
+
+Line
Inductance
50 microH
Line
Inductance
50 microH
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