1. No category

ECEN 405 Power Electronics
Test
Total marks: 45
Total time: 45 minutes
Please NOTE that the question format is different this year as discussed in the
class.
All questions to be answered. Allocate your time WISELY.
I. Answer the following:
[20 Marks]
1. What is complex power S?
2. State three main power switch losses?
3. Define what we mean by discontinuous current operation.
4. Discuss bipolar and uni-polar switching in DC-AC inverters.
5. Discuss the reason(s) on the cause of harmonics in high frequency
switching?
6. What parameters do you need to select an inductor for a buck
converter?
7. State two difference between boost and buck-boost converters.
8. What is a cuk converter? How does it differ with buck-boost
converter?
9. In Haywards substation, what was the switching frequency of the
thyristors?
10. List any two safety aspects that were discussed in the safety training at
Haywards.
II.
[5 Marks]
In the circuit shown, Vin  100V and I 0  10 A . During turn-on of
the MOSFET, the drain current has risen to iD  8 A . If the diode
forward voltage drop is VFM  1.0V , what is the value of vDS
across the MOSFET at this time?
III.
[5Marks]
In the MOSFET of a switching power-pole, the average power
dissipation is 30 Watts. The junction temperature of this MOSFET
must not exceed 1000⁰C, and the ambient temperature is given as
400⁰C. Calculate the maximum thermal resistance that can be present
between the ambient and the MOSFET junction.
IV.
[5 Marks]
In a Buck converter operating in steady state, the input voltage is 20 V,
the output voltage is 12 V and the output power is 60 W. The
switching frequency is 200 kHz. It is designed such that the peak-peak
ripple in the inductor current doesn’t exceed 2 A.
Calculate the minimum value of the inductance that must be used.
V.
[5 Marks]
In a buck-boost converter, Vin = 5V, V0 = 12V, fs = 200Hz and the
peak-peak ripple in the inductor current is 3A. The converter is
operating at the boundry of CCM and DCM. Find the value L of the
inductor.
VI.
[5 Marks]
A Boost converter is to be designed with the following requirements:
Vin = 5V, Vout = 12V, maximum power output is 40W. The switching
frequency is 400kHz. Assume ideal components. Estimate the value of
L if the converter is to remain in CCM at 1/3rd the maximum power
output.