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Table of contents
1.
Introduction
2.
Power Electronics Interview Questions for Freshers
2.1.
1. What is the power diode?
2.2.
2. What is Snubber Circuit?
2.3.
3. What is hard switching of the thyristor?
2.4.
4. What is Firing Angle?
2.5.
5. What is Universal  Motor?
2.6.
6. What is meant by PMDC?
2.7.
7. What is Reverse Power Relay?
2.8.
8. What are the several ways to enable SCR?
2.9.
9. What are Chopper's control strategies?
2.10.
10. Why is a tertiary winding used in a forward converter?
2.11.
11. What kind of switch is utilized in a switched-mode power supply?
2.12.
12. What time does a thyristor turn on?
2.13.
13. Why is it preferable to use a multiphase rectifier rather than a single-phase rectifier?
3.
Intermediate Power Electronics Questions and Answers
3.1.
14. What, in your opinion, is the main application for power electronics?
3.2.
15. Distinguish between a circuit breaker and an isolator?
3.3.
16. What conditions must be met for a gate pulse to activate an SCR?
3.4.
17. What distinguishes holding current from latching current in an SCR?
3.5.
18. What are the benefits of a GTO over a traditional thyristor?
3.6.
19. What function does the inter group reactor serve in a circuit for a single phase cyclo-converter?
3.7.
20. For high-frequency applications, which would you pick: MOSFET or IGBT?
3.8.
21. Why does a single-phase half-controlled bridge rectifier have a higher input power factor than a fully controlled bridge rectifier when both are powering RL loads at the same firing angle?
3.9.
22. What benefits come with using freewheeling diodes?
3.10.
23. Why is stepper motor efficiency so low?
4.
Advanced Power Electronics Questions and Answers
4.1.
24. Which do you think is better for high voltage applications, MOSFET or IGBT?
4.2.
25. What fundamental and necessary specifications must we obtain from the customer in order to construct the buck converter?
4.3.
26. What benefits does GTO have over SCR?
4.4.
27. List some of the purposes for a controlled rectifier.
4.5.
28. What does the term "inversion mode" mean?
4.6.
29. What are the various sorts of chopper configurations?
4.7.
30. Why are thyristors and diodes connected in antiparallel in inverter circuits?
4.8.
31. What are some uses for a series inverter?
4.9.
32. What are the drawbacks of the harmonics present in the inverter system?
4.10.
33. Compare CSI and VSI.
5.
Frequently Asked Questions
5.1.
How do I prepare for a power electronics interview?
5.2.
What are the basic electronics questions asked in interview?
5.3.
What are the main topics in power electronics?
6.
Conclusion
Last Updated: Mar 27, 2024
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Most Asked Power Electronics Interview Questions and Answers

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Introduction

Power electronics is a broad field of electrical engineering. It concerns the processing, control, and conversion of electric power. High voltages and currents are used in power electronics to supply power to electrical equipment and devices. These devices range from home air conditioners to industrial machinery. Over 80% of all generated power is reprocessed or repurposed through power electronic systems worldwide.

power electronics interview questions

 

In this article, you will interact with some power electronics interview questions. Examining typical interview questions could enable you to be successful when applying for jobs in this industry.

Power Electronics Interview Questions for Freshers

Let us now become acquainted with some important power electronics interview questions. You can toggle between easy, medium, and hard questions depending on your interviewing process.

1. What is the power diode?

Ans. A power diode is a diode that has two terminals, an anode and cathode, and two layers, P and N, and is used in power electronics circuits. This diode is more complicated in both its design and operation due to the modifications required to make low-power devices suitable for use in high-power applications. 
This diode performs a crucial function. It can be utilized as a rectifier in converter circuits, voltage regulation circuits, flyback/freewheeling diodes, reverse voltage protection, etc.

2. What is Snubber Circuit?

Ans. It is an electronic device that is used for suppressing voltage spikes that occur during the switching operations of relays and transistors. Voltage spiking is undesirable as it can damage the switching components of a circuit. It consists of a resistor and capacitor connected in parallel. They are commonly used in power supplies, inverters etc.

3. What is hard switching of the thyristor?

Ans. Hard switching of thyristor is the process of turning it off or on when it is under high voltage or high current conditions. It generates voltage spikes in the thyristor and stresses on the surrounding components. Snubber circuits can be used for suppressing the voltage and current transients generated due to hard switching.

4. What is Firing Angle?

Ans. Firing angle is used for defining the angle of time delay between the zero-crossing of the input voltage waveform and the triggering of the thyristor to start conducting current. It is commonly known as the conduction angle or delay angle. The average power delivered can be controlled by adjusting the firing angle.

5. What is Universal  Motor?

Ans. Universal Motor is characterized as a motor that can run at nearly the same speed and output, whether it is powered by a, single-phase AC or DC supply.

The universal motor has the same construction as a series DC motor. Although both motors have identical internal and external appearances, a series DC motor cannot be operated as a universal motor.
Due to their low efficiency (between 25% and 35%), we are unable to use these motors in industrial applications. It features a high beginning torque and a characteristic of changeable speed. With no load, it operates at a dangerously fast speed.

6. What is meant by PMDC?

Ans. Permanent Magnet DC Motor is referred to as PMDC. Permanent magnet DC motors are more advanced than induction motors. Torque is generated by utilizing the power of electromagnetic principles. Permanent magnets are used to create the field poles of this particular type of DC motor.

For these motors, three different permanent magnet types are employed: 

  1.  Alnico Magnets
     
  2. Magnets made of ceramic
     
  3. Magnets made of rare earth
     

The main benefits of PMDC motors are low noise, small size, great efficiency, and affordable manufacture.

7. What is Reverse Power Relay?

Ans. The reverse power relay is a protective relay that prevents power from flowing backwards. When a generator runs in parallel with a utility or another generator, the relay prevents power from the bus bar or another generator from flowing back to the active generator when its output fails.

8. What are the several ways to enable SCR?

Ans. Different methods to enable SCR are 

  1. Forward voltage triggering
     
  2. Gate Triggering
     
  3. dv/dt triggering
     
  4. Temperature triggering
     
  5. Light triggering

9. What are Chopper's control strategies?

Ans. The control strategies of the chopper are

  1. Pulse Width Modulation
     
  2. Frequency Modulation
     
  3. Current Limit Control

10. Why is a tertiary winding used in a forward converter?

Ans. A tertiary winding is added to the Transformer in a forward converter so that the magnetizing current can return to the input source instead of cutting off the transistor. At the conclusion of each cycle, the Transformer's magnetizing current must be reset to zero. Without it, the Transformer might be pushed into saturation, harming the switching mechanism.

11. What kind of switch is utilized in a switched-mode power supply?

Ans. Metal-oxide-semiconductor field-effect transistor (MOSFET), which is employed in high-frequency operations, is the switching component in a switched mode power supply ”(SMPS)” . We need high-frequency operational devices like MOSFET in SMPS.

12. What time does a thyristor turn on?

Ans. When a thyristor has to switch on, a positive gate voltage is provided between the gate and the cathode. Charges are introduced into the inner layer, and the voltage at which forward breakdown occurs is lowered when the gate current is established. The forward breakdown voltage is lower, the higher the gate current.

13. Why is it preferable to use a multiphase rectifier rather than a single-phase rectifier?

Ans. Multiphase rectifiers are preferred for the following reasons:

  • Increased DC voltage.
     
  • Improved Transformer utilization rate.
     
  • More favorable input power factor.
     
  • Output current has less ripple content.
     
  • Lower ripple frequency due to smaller filter circuit characteristics.
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Intermediate Power Electronics Questions and Answers

We provide a list of 10 medium level power electronics interview questions in this segment. Examining typical interview questions could enable you to be successful when applying for jobs in this industry.

14. What, in your opinion, is the main application for power electronics?

Ans. Power electronics assists engineers in designing high-efficiency electrical systems for lighting, automation equipment, motor controls, and sophisticated microprocessor utilities. Power electronics concepts can be applied to the following fields:

  • Rectifier and inverter applications, 
  • Chopper applications,
  • Cyclo-converter applications,
  • AC to DC, DC to AC, AC to AC, and DC to DC conversion. 

Rectifier and inverter use include 

  • Electroplating,
  • Improved charging, 
  • Variable DC drives, 
  • Emergency lighting systems,
  • Uninterrupted power supply,
  • Frequency converters.

Rectifier and inverter circuits are used to convert AC to DC and DC to AC circuits.

15. Distinguish between a circuit breaker and an isolator?

Ans. Circuit breakers automatically activate in the event of a system error, however, isolators must not be used with a load. Both switches, isolators and circuit breakers, serve connections between circuit components and a power system.
In order to disconnect downstream and upstream circuits when fixing downstream circuits, isolators are manually operated off-loading devices. In the event of overload faults, short circuits, and other failures, circuit breakers are helpful on-load devices for severing circuits. Additionally, isolators have a lower breaking capacity than circuit breakers.

16. What conditions must be met for a gate pulse to activate an SCR?

Ans. The following conditions must be met for an SCR to be activated by a gate pulse:

  • The forward-biased mode of SCR should be used between the gate and cathode, a positive gate voltage.
     
  • To make sure that the anode current exceeds the latching current, the gate pulse width should be set.

17. What distinguishes holding current from latching current in an SCR?

Ans. The latching current, which is associated with the SCR turn-on procedure, is the minimal current needed by the anode to maintain the forward conduction condition after the gate current has been removed. 

The holding current, which has to be reached by an anode in order for it to achieve an off status, is related to the SCR turn-off process. If the latching current, for instance, is 5 mA, then the holding current can halt conduction if it falls below 5 mA.

18. What are the benefits of a GTO over a traditional thyristor?

Ans. In comparison to a traditional thyristor, a GTO(Gate Turn-off thyristor) has the following advantages:

  1. GTO switches more quickly.
     
  2. Its ability to handle surge current is comparable to that of an SCR.
     
  3. At turn-on, it has a higher di/dt rating.
     
  4. GTO circuits are smaller and lighter than SCR circuit units.
     
  5. GTO is more effective.
     
  6. Due to the removal of commutation chokes, the GTO unit's acoustical, electromagnetic noise has been minimized.

19. What function does the inter group reactor serve in a circuit for a single phase cyclo-converter?

Ans. There will be a net potential difference across the two converters, which causes a circulating current even though the output voltages of the two converters have the same average value and different output voltage waveforms as a function of time. An Inter-group reactor can be inserted to stop this circulating current. Therefore, circulating current is limited using intergroup reactors.

20. For high-frequency applications, which would you pick: MOSFET or IGBT?

Ans. Given that a MOSFET has lower switching losses than an IGBT when used in high-frequency applications doing so may be advantageous. The ideal practice is to limit the frequency range for high-frequency applications to 200 kHz and for low-frequency applications to 20 kHz. The cost advantage of MOSFET over IGBT is another perk of this technology.

21. Why does a single-phase half-controlled bridge rectifier have a higher input power factor than a fully controlled bridge rectifier when both are powering RL loads at the same firing angle?

Ans. Even after having the same firing angle, a single phase half controlled bridge rectifier has a higher input power factor than a fully controlled bridge rectifier because some energy is returned to the source by the inductor in a completely controlled bridge rectifier, the input power factor of a single phase half bridge rectifier is larger than that of a fully controlled bridge rectifier of RL load for the same firing angle.

Consequently, less electricity will be sent to the load. Where supplied power to load/source volt-ampere equals power factor of input supply.

22. What benefits come with using freewheeling diodes?

Ans. The following are the benefits of utilizing freewheeling diodes:

  • Improved input power factor Greater load current waveform leads to improved load performance. 
     
  • During the freewheeling phase, energy held in L is transferred to R, increasing converter efficiency overall. 
     
  • The load voltage V0 is prevented from going negative by the freewheeling diode.

23. Why is stepper motor efficiency so low?

Ans. In contrast to Dc motors, the current consumption of a stepper motor is independent of load. When they are not working at all, they draw the most current. They consequently frequently run hot. At high speeds, the impedance increases, which results in a decrease in the voltage needed to run the constant current control.

Click on the following link to read further: Javascript Interview Questions and Answers

Advanced Power Electronics Questions and Answers

In this section, we offer a list of 10 advanced power electronics interview questions. 

24. Which do you think is better for high voltage applications, MOSFET or IGBT?

Ans. IGBT is required for high-voltage applications. MOSFETs are low voltage electronics, hence. They have a lower voltage rating than IGBT, for example. Generally speaking, MOSFETs are appropriate for applications with breakdown voltages under 250V. Applications with a breakdown voltage of up to 1000V are suitable for IGBTs.

25. What fundamental and necessary specifications must we obtain from the customer in order to construct the buck converter?

Ans. The customer must provide the following information to us:

  1. The voltage at Output Voltage input VOUT VIN
     
  2. Current Output (load current) IOUT
     
  3. Maximum voltage permitted for ripple on the output side
     
  4. The converter's effectiveness

26. What benefits does GTO have over SCR?

Ans. Some of the benefits of GTO over Scr are mentioned below:

  • Reduction in cost, weight, and volume due to eliminating forced commutation's commutating components.
     
  • Reduction of commutation chokes results in a decrease in electromagnetic and acoustic noise.
     
  • Increased turn-off speed that allows for high switching frequency.
     
  • Improved converter effectiveness.

27. List some of the purposes for a controlled rectifier.

Ans. The purposes of a controlled rectifier are:

  • Dc motor drives are used in steel rolling mills, printing presses, textile mills, and paper mills.
     
  • Traction DC
     
  • Processes involving electrochemistry and electrometallurgy
     
  • Drives for portable hand tools
     
  • Power sources with magnets
     
  • Transmission system using HVDC

28. What does the term "inversion mode" mean?

Ans. The voltage at the dc terminal in a single phase full converter over 900 is negative. Power thus flows from source to load, and the converter functions as a line commutated inverter. Current is positive while source voltage Vs is negative. This is referred to as synchronous mode or inversion mode.

29. What are the various sorts of chopper configurations?

Ans. Choppers can be categorized into the following types based on the direction of the current and voltage.

  1. Chopper in the First Quadrant, Type A
     
  2. Chopper from the Second Quadrant, Type B
     
  3. Type B helicopter with two quadrants or Type C
     
  4. A Type C or Type D two-quadrant helicopter
     
  5. Type E or four-corner helicopter 

30. Why are thyristors and diodes connected in antiparallel in inverter circuits?

Ans. When the main thyristors are turned off, the diodes linked in antiparallel will still permit the current to flow since the load current for RL loads will not be in phase with the load voltage. This is why we connect thyristors and diodes antiparallel. They are known as feedback diodes.

31. What are some uses for a series inverter?

Ans. At a high output frequency, between 200 Hz and 100 kHz, the thyristorised series inverter generates a waveform that is roughly sinusoidal. Induction heating, sonar transmitters, ultrasonic generators, and fluorescent lights are a few examples of fixed output applications where it is frequently employed.

32. What are the drawbacks of the harmonics present in the inverter system?

Ans. The major drawbacks are the following:

  • Harmonic currents will cause the induction motors to overheat. The motor's ability to support a load will be reduced as a result.
     
  • Harmonics from power rides can interfere with the operation of the control and regulating circuits if they are not properly protected. This can lead to malfunctions.
     
  • Harmonic currents result in losses in the ac system and, on occasion, even resonance. Resonance circumstances may impact the instruments and metering.
     
  • Torque pulsation caused by the harmonic current can be helpful on critical loads.

33. Compare CSI and VSI.

Ans.

VSI (Voltage Source Inverter)

CSI (Current Source Inverter)

A DC voltage source with a low or insignificant impedance supplies power to the VSI. A DC voltage source with a high impedance provides CSI with a variable current source.
The nature of the load impedance determines the waveform and magnitude of the load current. A DC voltage source with a high impedance provides CSI with a variable current source.
VSI requires feedback diodes. The CSI does not require any feedback diodes.
In VSI diodes are connected in parallel. In CSI diodes are connected in series.

Frequently Asked Questions

How do I prepare for a power electronics interview?

To prepare for a power electronics interview, first of all, you must clear all your core concepts regarding power electronics. Then, you should look over the previously asked interview questions to find out the pattern and level of the questions. Finally, you should work on you confidence and communication skills.

What are the basic electronics questions asked in interview?

Some primary electronic questions asked in an interview are: What is a passband? What is an ideal voltage source? How and when do you use a resistor? How to use a capacitor? What is a diode? What do you mean by thermal conductivity?

What are the main topics in power electronics?

The main topics in power electronics are electronic circuits, silicon carbide, thermal conductivity, capacitors, diodes, gallium nitride, dielectric material, semiconductor physics, electric motors, mechanical actuators, control systems, electromagnetic devices, etc.

Conclusion

We ended up going over power electronics interview questions in this article, which were divided into easy, medium, and difficult levels. It is an excellent resource for learning about power electronics. We hope these interview questions will assist you in preparing for your dream career.

We advise you to read a few of our interview articles to broaden your knowledge.

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Refer to our Guided Path to upskill yourself in DSACompetitive ProgrammingJavaScriptSystem Design, and many more! If you want to test your competency in coding, you may check out the mock test series and participate in the contests hosted on Coding Ninjas Studio!


But suppose you have just started your learning process and are looking for questions from tech giants like Amazon, Microsoft, Uber, etc. For placement preparations, you must look at the problems, interview experiences, and interview bundles.

All the best, and Happy learning!

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