EEIQS 1- Electrical Interview Questions On Power Electronics MCQs

It is the smartest collection of Electrical Interview Questions On  Power Electronics ,MCQs On Power Electronics which are asked in most of the interviews and competitive exams like GATE (India),PGCET..etc.

Power Electronics Interview Questions:-

[Q-1]What is latching current?
[A]It is defined as minimum value of anode current which it must attain during turn on process to maintain conduction when gate signal is removed.


[Q-2]What is holding current?
[A]It is defined as minimum value of anode current below which the SCR gets turned off.

[Q-3]What is AC voltage controller?
[A]It is defined as the power electronics converter which converts the fixed AC voltage into a variable AC voltage without change in the frequency.

[Q-4] What are the different turn on methods of SCR?
[A]Forward voltage triggering,Gate Triggering,dv/dt triggering,Temperature triggering,Light triggering

[Q-5]What is spread time of SCR?
[A]The time taken by anode current to reach from 0.9Ia to Ia.

[Q-6] What is meant by SOA of SCR?

[A]SOA – Safe Operating Area determines the voltage and current boundary within which the Power Device can be operated without destructive failure.

[Q-7] What is chopper?

[A] Chopper is a power electronics circuit which converts fixed value of DC to variable DC output.

Frequently asked Power Electronics interview questions

[Q-8] What is meant by commutation?

[A]The process of changing the polarity of the voltage across the terminals of SCR is called commutation.

or 

Simply turing off process of SCR 

[Q-9]what is the turn off time of half converter with R load?

[A] T= π/ ω;

 where ω=2πf

f=frequency 

π in rad

[Q-10]What is forced commutation?

[A]The process of the reversal of current through thyristor(SCR) by an external circuit is called forced commutation.

[Q-11] What is meant by cyclo-converter?

[A]cyclo-converter is a power electronic circuit which converts AC power at one frequency to other frequency.

[Q-12] What is firing angle?

firing angle defined as the angle measured from the instant SCR gets forward biased to the instant it is triggered.

[Q-13] Silicon based rectifiers are preferred than germanium based rectifiers because

(a) Si is available easily compared to Ge

(b) Only Si has a stable off state

(c) Ge is very temperature sensitive

(d) Si only has the characteristics α1 + α2 < 1 at low collector currents and reaches 1 at high currents

Which of the above statements are true?

Options:

1. A, B, D

2. B, D

3. B Only

4. D Only

[A] 2

[Q-14] What is step down cyclo-converter?

[A]It is the converter whose output frequency is less than the input frequency.

[Q-15] What is step up cyclo-converter ?

[A]It is the converter whose output frequency is more than the input frequency.

[Q-16] What is duty cycle of a chopper?

[A]It is the ratio of the ON time of the chopper to total time period of the chopper.

D = Ton / [Ton + Toff]

[Q-17]SCR based converter,what is the use of free wheeling diode?

[A]Conduct current during the OFF period of the SCR and to reduce negetive peak voltage in RL & RLE loads.

[Q-18] What is meant by pulse triggered devices?

[A]As the name indicates, to trigger these devices just a pulse is sufficient. Continuous gate voltage of entire on time is not required. The advantage of pulse triggering is, it will avoid the hard triggering.

Ex. Thyristor, GTO

[Q-19] " Six MOSFETs connected in a bridge configuration (having no other power device) MUST be operated as a Voltage Source Inverter (VSI) ". This statement is 

A. True, because being majority carrier devices, MOSFETs are voltage driven

B. True, because MOSFETs have inherently anti parallel diodes

C. False, because it can be operated both as current source Inverter (CSI) or a VSI

D. False, because MOSFETs can be operated as excellent constant current sources in the saturation region.

[A] D

[Q-20] What is meant by GTO?

[A]GTO-gate turn off thyristor It is a three terminal, four layer PNPN  Power Semiconductor device that can be turned on by a positive gate current and can be turned off by a reverse gate current.

[Q-21] What does 10V AC mean? Is it the RMS voltage or Peak voltage or Average voltage?

[A]In general,  AC voltages and currents are mentioned in RMS values only. It is sensible to compare with steady DC voltages and currents.

For example 230V AC supply means, 230Vrms AC Supply.

[Q-22] When we have to connect the SCRs in a parallel manner?

[A]To meet the high current demand we will connect the SCRs in a parallel manner.Similarly to meet the high voltage demand we have to connect the SCRs in series.

[Q-23] What is AC voltage controller?

It is defined as the power electronics converter which converts the fixed AC voltage into a variable AC voltage without change in the frequency.

[Q-24] What is inverter? What are the types of Inverter?

[A]A device which converts dc power into ac power at desired output voltage and frequency is called as Inverter.

Inverters are broadly classified into

Voltage Source Inverter (VSI)

Current Source Inverter (CSI)

[Q-25]Circuit turn-off time of an SCR is defined as the time 

A. Taken by the SCR to turn off

B. Required for SCR current to become zero

C. For which the SCR is reverse biased by the commutation circuit

D. For which the SCR is reverse biased to reduce its current below the holding current

[A]C

Above we shared some basic interview question on power electronics for electrical engineers.