Questions on Power Electronics
Here we have formulated question on Power electronics which will be helpful for not only electonics and communication engineering students for there semester exams but may be helpful during different job , placement interview , viva questions
Time allowed : 3hours Maximum marks : 100
Note : Attempt any five questions by selecting at least one from each unit.
1. Describe the construction and characteristic of Schottky diode. 20
ans. The Schottky diode also known as hot carrier diode is a semiconductor diode with a low forward voltage drop and a very fast switching action. The cat’s whisker diode used in the early days of wireless can be considered primitive Schottky diodes.
2. What are the limitations of R and R-C firing circuits ? 20
ans. The circuit with just resistance will have no timing function, it will simply limit the trigger current, hopefully to a safe value. The RC circuit will have a timing function, the capacitor will take time to reach 75% of its fully charged state when charged though a resistor.
3. How does power diode differ from ordinary P-N- junction diode ? 20
4. Draw the characteristics of SCR and explain its operation. 20
ans. It is a four-layer device with three terminals, namely, the anode, the cathode and the gate. When the anode is made positive with respect to the cathode, junctions J1 and J3 are forward biased and junction J2 is reverse-biased and only the leakage current will flow through the device.
5. Explain the operation of a six-pulse converter. How does it compare with 12- pulse
converter ? 20
ans. Six-pulse diode rectifiers work fine when you want a fixed DC voltage. When a controlled voltage is needed, a thyristor-fired phase-controlled rectifier may be preferred.
6. What do you mean by dual converter, how is it distinct from an ordinary converter ? 20
ans. Dual converter means it converts ac to dc and again it converts dc to ac this phenomenon of converting two types of signal are in the same circuit is called as dual converter.
7. Discuss four quadrant chopper. How is it different from one and two quadrant choppers ? 20
ans. The high-level schematic shown below is built from four main blocks. The DC motor and the Diode devices (within the Universal Bridge block) are provided with the SimPowerSystems library. More details on these two blocks are available in the reference sections of these blocks.
8. Write a short note on non – circulating type cycloconverter. 20
ans. A non- cycloconverter converts a constant voltage, constant frequency AC Waveform to another AC waveform of a lower frequency by synthesizing the output waveform from segments of the AC supply without an intermediate DC link.