ELE754 Power Electronics
Assignment #1
INSTRUCTION:
Complete AT LEAST FIVE from the following 10 questions. Show your name, ID and section
number (or your TA’s name) on the first page. Your TA will only mark the first five questions
with equal weight. The due date is Oct. 19, 2006 before 6:00PM at ENG333.
BUCK CONVERTERS
Q1. A buck converter has an input voltage, Vd  15 V. The required average output voltage
Vo  5 V and the peak-to-peak output ripple voltage is 10mV. The switching frequency is 20KHz.
The peak-to-peak ripple current of the inductor is limited to 1A. The converter is operating in
continuous current mode. Determine:
a) the duty cycle D,
b) the filter inductor L,
c) the filter capacitor C.
d) and the boundary current ILB.
Q2. If the above converter is supplying the load, RL  20 . The output voltage is maintained at
5V. Determine:
a) the duty cycle D,
b) the peak-to-peak ripple current of the inductor I L ,
c) and the peak-to-peak output voltage ripple Vo ,
Q3. Sketch scale to draw following waveforms when the above converter is operating at
RL  20 .
a) the inductor current and voltage waveforms, i L and v L ,
b) the current and voltage waveform of the MOSFET Qs, iQS and vQS ,
c) the capacitor current and voltage waveforms, iC and vC
BOOST CONVERTERS
Q4. A boost converter has an input voltage, Vd  6 V. The average output voltage Vo  15 V and
the average load current is I o  1 A. The switching frequency is 10KHz. If L  250 H and
C  440 F . Determine:
a) the operation mode
b) the duty cycle D,
c) the ripple current of the inductor I L ,
d) and the ripple voltage of the capacitor VC
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ELE754 Power Electronics
Assignment #1
Q5. If the above converter is supplying the load, RL  100 . The output voltage is maintained at
15V. Determine:
a) the duty cycle D,
b) the peak-to-peak ripple current of the inductor I L ,
c) and the peak-to-peak output voltage ripple Vo ,
Q6. Sketch scale to draw following waveforms when the above converter is operating at
RL  100 .
a) the inductor current and voltage waveforms, i L and v L ,
b) the current and voltage waveform of the MOSFET Qs, iQS and vQS ,
c) the capacitor current and voltage waveforms, iC and vC
CHOPPERS
Q7. A one quadrant chopper is feeding RL load with input voltage Vd  220 V. The load R  5 ,
L  15.5 mH. The switching frequency is 1kHz. The duty cycle is 40%. Calculate:
a) the minimum instantaneous load current.
b) the peak instantaneous load current.
c) the peak-to-peak ripple load current.
d) the average load current and average load voltage.
Q8. If the load is RLE load in the above converter, R  5 , L  15.5 mH, E=80V. Determine:
a) The operation mode
b) the peak instantaneous load current.
c) the peak-to-peak ripple load current.
d) the average load current and average load voltage.
Q9 If a two quadrant chopper is supplying the above RLE load. The duty cycle of upper device is
40% and the switching frequency is 1kHz. Calculate:
a) the minimum instantaneous load current.
b) the peak instantaneous load current.
c) the peak-to-peak ripple load current.
d) the average load current and average load voltage.
Q10 Sketch scale to draw the current and voltage waveforms in ALL FOUR switching devices
(MOSFETs and diodes) in Q9.
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