Name of the College : Noorul Islam College of Engineering
University : Anna University
Degree : B.E
Department : Electrical & Electronic Engineering
Subject Code/Name : EE 1301 – Power Electronics
Document Type : Question Bank
Website : niceindia.com
Download Question Bank: https://www.pdfquestion.in/uploads/niceindia.com/2995-EE1301-Power_Electronics.pdf
NICE Power Electronics Question Paper
1. Why IGBT is very popular nowadays? :
a. Lower hate requirements
b. Lower switching losses
c. Smaller snubber circuit requirements
Related : Noorul Islam College of Engineering EE1302 Protection & Switchgear B.E Question Bank : www.pdfquestion.in/2993.html
2. What are the different methods to turn on the thyristor? :
a. Forward voltage triggering
b. Gate triggering
c. dv/dt triggering
d. Temperature triggering
e. Light triggering
4. IGBT is a voltage controlled device. Why? :
Because the controlling parameter is gate-emitter voltage.
5. Power MOSFET is a voltage controlled device. Why? :
Because the output (drain) current can be controlled by gate-source voltage.
6. Power BJT is a current controlled device. Why? :
Because the output (collector) current can be controlled by base current.
8. What are the different types of power MOSFET? :
a. N-channel MOSFET
b. P-channel MOSFET
9. How can a thyristor turned off? :
A thyristor can be turned off by making the current flowing through it to zero.
10. Define latching current :
The latching current is defined as the minimum value of anode current which it must attain during turn on process to maintain conduction when gate signal is removed.
11. Define holding current :
The holding current is defined as the minimum value of anode current below which it must fall to for turning off the thyristor.
12. What is a snubber circuit? :
It consists of a series combination of a resistor and a capacitor in parallel with the thyristors. It is mainly used for dv / dt protection.
13. What losses occur in a thyristor during working conditions? :
a. Forward conduction losses
b. Loss due to leakage current during forward and reverse blocking.
c. Switching losses at turn-on and turn-off.
d. Gate triggering loss.
14. Define hard-driving or over-driving :
When gate current is several times higher than the minimum gate current required, a thyristor is said to be hard-fired or over-driven. Hard-firing of a thyristor reduces its turn-on time and enhances its di/dt capability.
15. Define circuit turn off time :
It is defined as the time during which a reverse voltage is applied across the thyristor during its commutation process.
16. Why circuit turn off time should be greater than the thyristor turn-off time? :
Circuit turn off time should be greater than the thyristor turn-off time for reliable turn-off, otherwise the device may turn-on at an undesired instant, a process called commutation failure.
17. What is the turn-off time for converter grade SCRs and inverter grade SCRs? :
Turn-off time for converter grade SCRs is 50 – 100 ms turn-off time for converter grade SCRs and inverter grade SCRs and for inverter grade SCRs is 3 – 50 ms.
18. What are the advantages of GTO over SCR? :
a. Elimination of commutation of commutating components in forced commutation, resulting in reduction in cost, weight and volume.
b. Reduction in acoustic noise and electromagnetic noise due to elimination of commutation chokes.
c. Faster turn-off, permitting high switching frequencies.
d. Improved efficiency of the converters.
19. What is meant by phase controlled rectifier? :
It converts fixed ac voltage into variable dc voltage.
20. Mention some of the applications of controlled rectifier :
a. Steel rolling mills, printing press, textile mills and paper mills employing dc motor drives.
b. DC traction
c. Electro chemical and electro-metallurgical process
d. Portable hand tool drives
e. Magnet power supplies
f. HVDC transmission system
21. What is the function of freewheeling diodes in controlled rectifier? :
It serves two process.
a. It prevents the output voltage from becoming negative.
b. The load current is transferred from the main thyristors to the freewheeling diode, thereby allowing all of its thyristors to regain their blocking states.
22. What are the advantages of freewheeling diodes in a controlled in a controlled rectifier? :
a. Input power factor is improved.
b. Load current waveform is improved and thus the load performance is better.