I have already mentioned the metric of power process. High efficiency is a must for any processing system. The primary reason for this is not to save money on one’s electricity bill or conserve energy. Rather, according to power rule, it is impractical to design a low-efficiency converter which can produce high voltage output.
The next thing that you need to know is the application of power electronics. A basic design is modified according to the need of the application. Let’s consider an aerospace application of power electronics. In the power system of an earth-orbiting spacecraft, a solar array produces the main power bus voltage. A DC-DC converter converts the bus voltage into the regulated voltage required by the spacecraft payloads. Battery charge controllers interface the main power bus to the batteries; this controller may also have a DC-DC converter. The power systems of almost all spacecrafts and aircrafts follow this simple scheme.
On the other hand, in an electrically driven vehicle, batteries are charged by converters that draw high-factor sinusoidal current from a single-phase or a three-phase AC line. The batteries supply power to the variable-speed AC motors to propel the vehicle. The speed of the AC motor is controlled by the variation of the electrical input frequency. The inverter produces three-phase variable output to control the speed of the motor as well as the vehicle. In some applications, a DC-DC converter steps down the original voltage to a lower level according to the electronics need of the systems.
The list of examples may be endless. So instead of mugging up the nitty-gritty of individual systems, try to understand the function of the individual elements, so that you can use them to design the power system of your choice. You may put special emphasis on various common systems to recheck your understanding. A general understanding of locomotives, battery chargers for telecommunications, inverter systems for applications involving renewable energy generation such as wind and photovoltaic conversion, and also general power utility systems may help you comprehend any unknown power system that you may come across.
Know the elements of power electronics
Undoubtedly, one of the things that makes power electronics interesting is its incorporation of elemental concepts from diverse set of fields. As a power electronics professional, you may come across the basics of analogue circuits, electronic devices, control systems, power systems, magnetics, electric machines and even numerical solutions.
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In the IT/ITES segment, with energy efficiency and reduction of operational costs becoming critical business goals, two major trends in data centre infrastructure design are notable today: power efficiency and power distribution.
—Pramod Agashe, COO of APW
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Thus the practice of power electronics requires a broad understanding of electrical as well as electronics engineering. In addition, there are fundamental concepts which are unique to power electronics and require specialised study.
Let’s start with the switching mode. High-frequency switching makes converter modeling the central element of your study. You need to know how to put a converter in equilibrium. The principles of steady-state converter analysis including inductor-volt-second balance, capacitor charge balance and small ripple approximation are of great importance. Try to get a clear idea of how these principles are applied in boost (capable of voltage increase), buck (capable of voltage decrease) and cuk (capable of inverting the voltage priority) converters. For example, ripple approximation greatly simplifies the analysis, especially in a well-designed converter where the switching ripples in inductor current and capacitor voltage are comparatively small with respect to the DC component.
Another important element is circuit modeling. You are expected to understand how the DC transformer model is manipulated and solved using conventional circuit analysis techniques. How the models can be refined to account for loss elements such as inductor-winding resistance and semiconductor ‘on’ resistance and voltage drops?
Realise the field
Now that you are aware of the basic elements, it’s time to realise the modus operandi of the actual devices. Switch realisation would be a good starting point. Knowledge about majority carrier devices like MOSFETs and minority carrier devices like BJTs, IGBTs and thyristors is must. Additional knowledge like the operation of unidirectional switches to handle discontinuous conduction mode, may give you an edge over your competitors.
Converter circuit is another important matter that needs thorough understanding. Basically, circuit manipulation, transformer isolation along with circuit evaluation and design related skill sets are in high demand. Try to get familiar with converter dynamics and control. The basic understanding of modelling and averaging approaches will be an added advantage.
In the next step, you have to perform the actual design job by applying all those techniques and concepts discussed so far. Controller design and input filter design are the two major challenges in this field.
Your next challenge is to provide a solution for real-life systems. Go beyond your textbook and enter your own power electronics design laboratory. Try to collect some problems pertaining to AC and DC equivalent circuit modelling and resonant conversion and chalk out possible solutions. Last but not the least, update yourself on the latest technological advances in this field.
Prepare for the future challenges
Bear in mind that technological advances are meant to increase energy efficiency and reduce operational cost. As a result, the present era is solely dedicated to green energy and energy-saving equipment. Understand this hidden demand and keep pace with it. Your final-year project may be on the utilisation of solar energy or wind energy to run a traditional power system—a solar power fuel dispenser, for example. In fact, there are many ingenious ways to improve power efficiency through various innovations.
According to industry veterans like Pramod Agashe, COO of APW, traditional power distribution units often fail to cope with today’s high-density computing environments, so designing of efficient power distribution system for data centres may be a good challenge. Any of these real problems may be your next food for thought.
Perhaps, at this moment the dilemma about your career prospect is driving you nuts. Boost up your brain. Dig down the power field. It will provide you not only a secure job but the opportunity to be an active part of a nation-building story.
