ABSTRACT
Power Electronics deals with the applications of solid state electronic devices in the control and conversion of electric power. Power Electronics has seen a tremendous growth in recent times and almost all the applications today use power electronic devices in some or the other form. Hence it becomes essential to study the advantages of these devices, which made it so popular.
CHAPTER ONE
- INTRODUCTION
The systems and machines of our world depend on power electronics for the ability to run efficiently and sustainably. Power electronics is the application of solid-state electronics for the control and conversion of electric power. It applies to both the systems and products involved in converting and controlling the flow of electrical energy, allowing the electricity needed for everyday products to be delivered with maximum efficiency in the smallest and lightest package.
The evolution of power electronics is over the past 100-plus years. It includes electrical machines, mercury-arc rectifiers, gas tube electronics, Mas, power semiconductor devices, converter circuits, and motor drives. Wherever possible it gives the name of the inventor and the year of invention for important technologies. It is important to note, however, that inventions are generally developed by a number of contributors working over a period of time. The history of power electronics is so vast that it is impossible to review it within a few pages. More information is available in the references.
Power electronics is a technology that deals with the conversion and control of electrical power with high-efficiency switching mode electronic devices for a wide range of applications. These include as dc and ac power supplies, electrochemical processes, heating and lighting control, electronic welding, power line volt–ampere reactive (VAR) and harmonic compensators, high-voltage dc (HVdc) systems, flexible ac transmission systems, photovoltaic and fuel cell power conversion, high-frequency (HF) heating, and motor drives. We can define the 21st century as the golden age of power electronics applications after the technology evolution stabilized in the latter part of the past century with major innovations.
Power electronics is ushering in a new kind of industrial revolution because of its important role in energy conservation, renewable energy systems, bulk utility energy storage, and electric and hybrid vehicles, in addition to its traditional roles in industrial automation and high-efficiency energy systems. It has emerged as the high-tech frontier in power engineering. From current trends, it is evident that power electronics will play a significant role in solving our climate change (or global warming) problems, which are so important.
Power electronics has recently emerged as a complex and multidisciplinary technology after the last several decades of technology evolution made possible by the relentless efforts of so many university scientists and engineers in the industry. The technology embraces the areas of power semiconductor devices, converter circuits, electrical machines, drives, advanced control techniques, computer-aided design and simulation, digital signal processors (DSPs), and field-programmable gate arrays (FPGAs), as well as artificial intelligence (AI) techniques.
The history of power electronics goes back more than 100 years. It began at the dawn of the 20th century with the invention of the mercury-arc rectifier by the American inventor Peter Cooper Hewitt, beginning what is called the “classical era” of power electronics. However, even before the classical era started, many power conversion and control functions were possible using rotating electrical machines, which have a longer history.
1.1 DEFINITION OF POWER ELECTRONICS
A field of electrical engineering that deals with the application of power semiconductor devices for the control and conversion of electric power.
1.2 OBJECTIVE OF THE STUDY
The main objective of this work is to deal with the study of the part of engineering that deals with the application application of power semiconductor devices for the control and conversion of electric power.
1.3 SCOPE OF THE PROJECT
The capabilities and economy of power electronics system are determined by the active devices that are available. Their characteristics and limitations are a key element in the design of power electronics systems. Formerly, the mercury arc valve, the high-vacuum and gas-filled diode thermionic rectifiers, and triggered devices such as the thyratron and ignitron were widely used in power electronics. As the ratings of solid-state devices improved in both voltage and current-handling capacity, vacuum devices have been nearly entirely replaced by solid-state devices.
1.4 SIGNIFICANCE OF THE STUDY
Mass Production: Due to huge development in the production techniques of semiconductor devices, these semiconductor based power electronic devices are now produced in huge bulk and hence have resulted into very low price. These devices are available in a variety of voltage and current ratings to choose from.
Highly Reliable: Since these devices have no mechanical moving parts, there are very less failure chances and hence has a very rugged performance and long life, provided it is operated under rated conditions.
Highly Efficient: In most of the applications these devices acts as a switch and we know that in both the modes of the switch, i.e. ON and OFF the power loss in it is very less, and the switching losses are also very low.
Negligible Maintenance: Again due to absence of mechanical moving parts, the power electronic systems require almost nil maintenance.
Fast: In comparison to mechanical or electro-mechanical devices the power electronic systems have way faster dynamic response.
Size: These power electronic systems are very small in size when compared to mechanical systems for similar power ratings and hence less weight, less floor space, less handling issues, less installation cost, less packing and transportation prices and many more.
1.5 LIMITATION OF THE STUDY
Power electronic systems suffer from some limitation also. The following are some of them:
Harmonics: this is the only serious disadvantages of power electronic systems that it injects considerable harmonics both the sides, to the connected load side and to the power source side. Since the converters alter the sinusoidal waveform according to the requirement, harmonics are generated in the output voltage and current of the converter and also in the input current to the converter. Now these harmonics create a lot of trouble on both the sides.
On the load side if we have motors, harmonics cause problems such as excess heating, more acoustic noise, torsional vibration of motor shaft, commutation issues in DC motors, etc. Hence nowadays we have special VFD motors which are designed to better handle the effects of harmonics. Apart from this we also have filter circuits to limit the harmonics to the load. On the supply side also harmonics create a lot of trouble. The performance of other equipments connected to the same supply is seriously affected. Harmonics in supply lines also leads to radio interference with communication lines, audio and video equipments. Apart from this the input side transformer also gets overheated and its efficiency gets reduced. Special converter transformers are used when the output has considerable power electronic systems, such as motor drives in industries. Harmonics also increases skin effect in the cables and hence more heating. Thus we need to install filters in the input side also.
Low Power Factor: Certain power electronic converters operate at very low input power factor and hence it might be required to install reactive power compensation equipments.
Low Overload Capacity: Power electronic devices work on rated voltage and current provided proper heat evacuation system is provided. Excess current causes hot spots at junctions and burning of devices. High dv/ dt leads to false triggering and hence a power electronic device along with it needs compulsory protection arrangements such as snubber circuit etc.
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