How to prepare for

How to prepare power electronics for GATE and ESE?

For Electrical engineers, Power Electronics is one of the important core topics that one cannot skip when it comes to GATE and IES exam preparation. ESE exam is one of the most sought-after exams among technical graduates. It provides opportunity for graduates to work within their technical boundaries for the government along with all the facilities, dignity and career growth that an individual may seek. To clear the ESE and GATE exam in minimal time though, it is inevitable that one follows the correct preparation strategy for IES preparation.  However, to spend a lot of effort and time in preparation of any one subjec,t is a waste of both and must be avoided at all costs. It is always a good idea to strategize and plan your preparation before starting it. In lieu of the same lines, we try to present the preparation strategy for Power Electronics in this blog so that aspirants get an idea of what exactly is important from ESE exam point of view and can plan their studies accordingly.

Why to study Power Electronics:

As a Power electronics engineer, you would be required to deal with control of high-power applications. This high power needs to be controlled and converted according to the requirements of load with high efficiency. To get an even better idea, consider a power generator like turbine, which requires 6 KW of steam input to generate 1 KW of power at output. Now one can imagine the amount of losses that would occur here and how important it is to minimize these losses as a responsible Power engineer, when you work for the government. Since renewable energy sources like solar energy and wind energy are the future of power generation, it becomes important to study and learn about the suitable power converters that are used. This becomes important since the generated power is in one form and requirement at the grid end in another energy form. To bridge this gap between generating station source and grid station is the responsibility of a Power Engineer by using suitable power converters, which can be learnt through Power Electronics basics. Thus, apart from studying Power Electronics for GATE and ESE, it becomes important as an Electrical engineer, to learn about all the basics and various applications of the subject.

Applications of Power Electronics:

It finds a number of applications in various streams of Electrical engineering, some of which have been enlisted here:

  • Power electronics is applicable in AC drives and DC drives. With complete knowledge of both, basics of this subject and Electric machines, one can get complete understanding of AC drives and DC drives which is nothing but control of various electrical machines.
  • To understand a number of advanced concepts of Electrical engineering like FACTS (Flexible AC Transmission System), power quality, HVDC and reactive power control.
  • Power electronics also finds application in various modern-day technologies like traction, hybrid cars, robotics, aircrafts, X-rays, scanning machines, medical laboratories and also in telecommunication where we use power electronic converters.

About Power electronics:

Power electronics engineers mainly deal with control, conversion and conditioning of electric power using semiconductor devices such as switches with high efficiency. Power conversion is necessary to omit the mismatch between available energy form the source and required energy form. For example, available supply energy maybe 230 Volt, 50 Hz, 1-phase or 400 Volt, 50 Hz, 3-phase. Sometimes energy is stored in solar batteries of 12 V, 48 V or renewable sources like photo-voltaic solar cells or wind turbines. Whereas the requirement is 1-phase for domestic applications like bulb or fan or 3-phase loads like high power Induction motors, pumps, DC motors for variable speed control, integrated circuits, microprocessor using DC of 15 V, 5 V, 3.3 V or 1.5 V. In addition, fluctuations in supply voltage needs to be regulated, called conditioning of power supply. All this gives an adequate idea about what Power electronics is about and what has to be studied and learnt in this topic for IES exam preparation. Next are various basics required to learn the subject most efficiently.

To understand Power electronics: Subjects

Understanding of this subject for ESE and GATE exam requires various concepts of a number of other subjects from IES Electrical engineering syllabus. Following is a list of the subjects and the important topics from each that might be required:

  • Network theory: Knowledge of Laplace transform and inverse Laplace transform is necessary to solve differential equations while solving numerical questions.
  • Electric Machines: To get understanding of fundamentals of drives, it is advisable to study Electric Machines before Power electronics.
  • Signals and systems: To analyze wave-forms, a thorough knowledge of Fourier series is necessary.
  • Power systems: Basic concepts of Power systems are required to learn about applications of like FACTS, Reactive Power Control, power quality and HVDC.
  • Semiconductor Physics: Basics of semiconductor physics and semiconductor switches help to learn about Power Electronics switches since they are based on semiconductor switches.
  • A basic idea of analog electronics, digital signal processing, microcontrollers may also be helpful for design of control circuits.

Weightage of topics:

Power Electronics in GATE generally has a weightage of 8 to 10 marks. Whereas in ESE prelims 15 to 20 marks are dedicated to this subject. In stage-2 or Mains of ESE exam, Power Electronics becomes even more important with a weightage of 40 to 70 marks. Few topics are common to both GATE and ESE exam, whereas three topics are exclusively included for ESE exam only. Following is a table presenting topic wise weightage for topics common to both GATE and ESE exam:

1.       Power semiconductor devices1-2 marks3-4 marks5-10 marks
2.       AC to DC converters2-4 marks4-5 marks10-20 marks
3.       DC to DC converters4-5 marks3-4 marks15-25 marks
4.       DC to AC converters
5.       AC and DC drives1 mark1-2 marks0-5 marks

Here, DC to DC converters and DC to AC converters carry more weightage, especially in GATE and also take less time to prepare. This is, thus, one part of Power electronics that becomes important from examination point of view and must be revised multiple times after preparation before the exam. AC and DC drives may not even be asked sometimes and carries very little weightage otherwise also. In case you have less time left for IES preparation or have other important topics to finish, you can leave it for end or may even omit it. AC to DC converters has more weightage in Mains of ESE exam, so maybe avoided at time of ESE prelims but is necessary to learn before ESE mains.

The table above gives a clear picture of the topic wise weightage of Power electronics for various stages and exams. one can plan their preparation strategy for this exam accordingly There are three topics in the syllabus, though that are included exclusively for ESE and carry a weightage of 2 to 4 marks for ESE Prelims and 5 to 10 marks for ESE Mains:

  • Resonant converters- Used to reduce the switching losses in power conductors, even at high frequencies.
  • High frequency transformers and inductors- To learn about and rectify the problems experienced at high frequency for magnetic components like transformers and inductors.
  • Switched Mode Power Supplies