Chapter 1 and 2 Summary Questions 2020 2.
1. Explain in full details the main objectives of power electronics.
2. Design a fully labelled block diagram of power electronics and explain the composition
of each stage.
3. List four types of converters and give one example for each.
4. Power switches are divided into three categories namely power diodes, silicon
controlled rectifiers (thyristors) and controllable switches all using semiconductor
material during fabrication. Appropriate explain these dissimilarities between power
diodes and SCR shown clearly in their operation and in their v-i characteristic curve.
5. Discuss in details the study of power electronics.
6. Two 1 200 V rated thyristors are connected in series across 2.2 kV supply. The forward
blocking characteristic of the first thyristor has a slope of 0.020 mA/V, the second
thyristor has a slope of 0.013333 mA/V. For this design;
a. Determine how these switches will share the voltage among them.
b. A voltage equalizing resistor of 6.5 kโฆ are then connected across each thyristor
as a measure to correct the apparent voltage imbalance voltage. Show the new
voltage sharing by these switches when these equalizing resistors.
c. Find also the power dissipated in the equalizing resistors.
d. What is the purpose of connecting power switches in series?
7. Explain in details how to switch (โon and offโ) an SCR, clearly mentioning all the key
parts that should be avoided or observed while doing so.
8. Two 30 A (T1 and T2) thyristors supply a load of 55 amperes. The voltage on-state
characteristic for the thyristors is as follows;
๐ฝ๐ป๐ = ๐. ๐ + ๐ฐ ร ๐. ๐๐๐ (V).
๐ฝ๐ป๐ = ๐. ๐ + ๐ฐ ร ๐. ๐๐๐ (V).
a. Determine which thyristors will carry the majority current.
b. If a small 0.22 โฆ small resistor is connected in series with each thyristors to
force more equal current sharing, compute the new currents.
c. Compute the voltage across the thyristors with and without the small series
resistors.
d. Name the purpose of using small series resistors and what are the
shortcomings of this approach.
9. Name two differences between linear and power electronics that resulted in power
electronics being more popular.
10. Briefly describe the different classes of semiconductor power switches and give an
example of each, drawing the respective circuit symbol.
11. List six applications of power electronics and give one example for each of these
applications.
