Wednesday, April 1, 2015

Power Electronics Interview Questions and Answers: Part-4

Power Electronics Interview Questions with Answers:

           Here, we had collected Various Power Electronics and Drives related Interview questions, Viva Questions. We are appending the new Q & A whenever we are getting from readers.
Some of the questions are asked to Experienced candidates based on their previous experience. If it is not related to your field, just ignore it.

[Q] 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] What is inverter? What are the types of Inverter?
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] What is chopper?
It is equivalent to a dc transformer in ac circuit. The Chopper is a static switch which is used to get the variable dc output voltage from a constant dc input voltage.
Chopper basics, types and principle of operation is discussed in a separate page. Click here to know more about Choppers

Step down chopper:
 In this circuit, the average output voltage [VO = D . VS] is less than the input supply voltage. It is also known as Buck converter.

Step up chopper:
It is also known as Boost converter. Here the average output voltage [VO = VS / 1 - D]  is more than the input supply voltage.

[Q] What is load commutation?
In load commutation, the load current flowing through the thyristor either becomes zero or is transferred to another device from the conducting SCR.

[Q] What is meant by pulse triggered devices?
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] What is level-sensitive devices? give some examples
Some of the level sensitive devices are
In order to keep these devices in the ON state condition, we have to apply  gate current/voltage continuously to these devices.

[Q] What is meant by GTO?
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] What are the types of GTO?
Asymmetrical GTO
Symmetrical GTO

[Q] What does 10V AC mean? Is it the RMS voltage or Peak voltage or Average voltage?
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] When we have to connect the SCRs in a parallel manner?
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] Define Gate Charge in MOSFET?
The gate charge is defined as the amount of charge required for the device during turn-on and turn-off time. It is the most important parameter we have to consider while selecting the MOSFET. The switching speed of the MOSFET depends on the speed at which the gate driver can charge or discharge the input gate charge.

More Power Electronics Interview Questions:
Power Electronics Interview Questions: Set-1
Power Electronics Technical Interview Questions

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