Elements of power electronics krein pdf free download

A few hours of Web browsing confirms how much misinformation exists about power electronics and design of conversion circuits. Modem devices have reached the point at which they no longer limit the applications. Imaginative designers have found a huge variety of solutions to many types of power electronics problems.

It is essential to develop a system-level understanding of the needs and techniques, since a device focus can be unnecessarily constraining. Even so, books continue to be published following the practice of past treatments. Unfortunately, these two books tend to be best suited for students pursuing advanced de- grees. This new book owes its roots to the Wood text, and shares the philosophy of the Kas- sakian text.

However, from the outset it was planned for undergraduate students or other en- gineers with no prior power electronics background. Why study power electronics? First, because it is fun. Power electronic circuits and systems are the basic energy blocks needed for things that move, light up, cook a meal, fire a combustion cylinder, or display information on a video monitor.

To most students, circuit laws are lifeless mathematical equations. A power electronics engineer needs a working under- standing of circuits, semiconductor devices, digital and analog design techniques, electro- magnetics as it affects layout and device action, power systems and machines, and the inner action of major applications. Third, because of the challenge. Since power processing is needed just about everywhere, there are few areas with more variety of design tasks.

A power electronics expert might work on a 10 MW backup system one day, and on a 1 W system for battery processing the next. Fourth, because of the opportunity.

The next personal com- puter you buy will have a power supply as big as the rest of its electronics combined. It will place extreme performance demands on the supply, and will require total reliability. The power supply will be a significant fraction of the cost to build the computer. Yet the com- puter manufacturer employs dozens of hardware-software engineers for every power elec- tronics engineer.

The need is there, and will grow. The book is organized into five parts. Four are here in your hands. Part V, the laboratory supplement, is available through a World Wide Web site.

In Part I, the framework for power electronics is established. The three chapters in Part I offer a historical perspective, and es- tablish key framework concepts such as switching functions, equivalent methods for filter design, diode circuit analysis, and regulation. Part I1 covers all the major converter classes- dc-dc, ac-dc, dc-ac, ac-ac, and resonant converters-in considerable depth.

Students are of- ten surprised to learn that they can become effective designers of useful converters by the time they are through Chapter 4. Chapter 8 presents perhaps the first undergraduate text ma- terial on the emerging subject of resonant converters.

Part I11 covers the issues of compo- nents, from models for sources and loads to power semiconductors to the circuits that drive them. Unique features include the fundamental approach to magnetics design, coverage of wire sizing and parasitic resistance effects, and extensive examples.

Part IV introduces con- trol methods, again at the undergraduate level. Chapters 15 and 16 discuss general control issues and develop the popular frequency domain design approach. Chapter 17 provides a new perspective on an especially simple approach to large-signal control.

The book is big because of the breadth of the field. At the University of Illinois, there is just one course at present. We attempt to cover Chapters , 11, and 12 in detail, with briefer treatments of and The chapters are relatively independent, so a variety of course arrangements can be supported. As prerequisites, students should recognize that all their basic course work in electrical en- gineering will be brought to bear for the study of power electronics.

Prior courses in circuits, in electronics, in systems, and in electromagnetics are essential. Prior courses in electro- mechanics, analog or digital circuit and filter design, and power systems can be helpful, but are not vital. A few things are not here. Space and time do not permit detailed coverage of individ- ual applications. Motor control and telecommunications power are two examples.

It is not possible to provide adequate coverage for dc or ac motor control, or for telecommunications power system design. Beyond the introduction in Chapter 6, the motor control application is left to books from others. The telecommunications application is left to a number of d c 4 c converter examples. The book makes extensive use of computer tools, and students are encouraged to fol- low this lead. However, no floppy disk is included because few readers find time to learn the programs on such disks.

Instead, several example listings are given in the Appendix. A group of industry-based students developed extensive Mathcad applications. Some of these can be found on the site. Additional problems will be posted as well. Instructors can request Web access to problem solutions through the publisher. A few words on chapter problems: In this book, a great many of the problems have a design orientation.

This means the problems are open-ended, and not always completely spec- ified. Students are encouraged to think about the context of a problem, and fill in informa- tion when necessary. There are no tricks here. In general, each problem attempts to describe a real system. There are some exceptions in magnetics and capacitive components, in which the centimeter is common as the unit of length.

If units are not listed explicitly, SI units should be assumed. Appendix B provides a review of some of the unit issues. The stan- dard gives procedures for creating combination symbols. Unusual symbols, such as that for an ideal ac current source, attempt to follow the procedures. There are dozens of numerical examples and hundreds of numerical problems in this text.

It is important to be aware of significant digit issues. A real circuit application com- monly has only about two significant digits.

Tolerances on capacitors, inductors, and timing elements are wide. However, in power electronics we are often interested in small differ- ences for efficiency measurements or other detailed information. It is important that small differences not be lost to round-off error in repeated calculations. In examples here, digits are carried through, and round-off is performed only as the last step in the computation. I am indebted to the many students who have given their insight and their active help in bringing this text about.

Richard Bass, now at Georgia Institute of Technology, shared many suggestions on the lab material and as we began to use these notes in place of a published text.

Pallab Midya, now at Motorola Corporation, along with Dr. Bass, provided some of the insights now present in Chapter 17 and in the lab sections of Part V. A special debt is owed to Riidiger Munzert, who spent many hours proofreading during his exchange visit from Technische Hochschule Darmstadt. He helped me simplify the English throughout the text, and made personal contributions to Chapter Final round preparation could not have been completed without the efforts of four cur- rent students.

Matthew Greuel created most of the lab figures. Daniel Logue found a way to build camera-ready computer output for simulation figures. Richard Muyshondt created sev- eral simulations and assisted with proofreading.

I am very grate- ful for all of this assistance. My colleagues in power electronics have made many constructive suggestions. The ideas from David Torrey of Rensselaer Polytechnic Institute have been particularly useful, and I appreciate the encouragement. The comments of Thomas Sloane of Alpha Technolo- gies were especially significant and challenging. Others provided encouraging comments too numerous to be mentioned here.

I am grateful for the support of my wife, Sheila Fitzgerald Krein, and family in this project. They have tolerated the long hours and extra workload with grace. It has been a dif- ficult time because of some family tragedies, and I deeply appreciate their forbearance. Many power conversion circuits and control techniques are the subject of active patent pro- tection. The author cannot guarantee that specific circuits or methods described in the text are available for general use.

This is especially true of resonant conversion material in Chap- ter 8. Power electronics by its nature is an excellent subject for laboratory study.

However, it brings many more hazards than more familiar areas of electronics. Readers who plan ex- perimental work in the field should take proper safety precautions in the laboratory.

Mathcad is a registered trademark of Mathsoft, Inc. Mathematica is a registered trade- mark of Wolfram Research, Inc. Matlab is a registered trademark of The Mathworks, Inc. Figure 1. Top: Niagara Falls. As we commemorate years since this invention and first practical use, electricity has become the energy of choice for modem life.

Electrical energy consumption continues to grow, especially as a fraction of all energy used. Let us take a few moments to consider why this medium is so important. Energy in electrical form has major advantages:. A few metal wires can transmit the energy needs of an entire city. It is atomic in character and thus comes in small packages. Virtually any energy need or power rate, from tiny communication circuits to gigawatt lasers, can be met electrically.

What about some of the alternatives? Moving water has been used as an energy source for centuries. The Niagara River in North America and the Nile River in Africa have enough flow and sufficient elevation change to provide many thousands of megawatts to surround- ing cities.

The simplest way to transport this kind of power by water is obvious: pipe a river to an energy destination point! A much cheaper method is to convert a river's energy in a hydroelectric plant, then move it over an electrical transmission line. All of the awe-inspir- ing energy represented by Niagara Falls the American side is shown in Figure 1. Heat is also common as a basic energy form.

In many large cities, low-pressure steam from power plants is piped to buildings as a source of space heat or process steam. The low temperature of any reasonable heat source precludes wide use of energy in this form. A one- volt battery, for example, has potential energy that corresponds to a thermal source at 50,OOO"C.

Waste heat cannot come close to the broad applications of any electrical source. Energy con- version from heat is another critical issue. All conversion is limited fundamentally by the Sec- ond Law of Thermodynamics and therefore by the Camot cycle efficiency.

In the case of ther- mal conversion, the Carnot limit is very restrictive. The Camot limit is much less important in electrical sys- tems. This is not to say that energy in electrical form does not come without problems. Con- sider that:. Energy storage in electrical form is difficult.

Electricity takes a wide range of different forms. The form best suited for large-scale en- ergy transport, for instance, is not the best form for digital logic circuits. Table 1. Storage remains one of the key limiting factors in the application of electricity. The only de- vice which actually stores electrons is the capacitor. The stored energy is given by k! The following example illustrates the feeble energy capabilities of typical capacitors. Example 1.

How much energy does this capacitor store? How long will this energy support a 60 W light bulb? A pF capacitor in a V circuit stores iCV2, or The energy stored in this capacitor will keep the bulb burning for At higher voltage, perhaps V, the capacitor can maintain the bulb for 3. A one-liter capacitor can store a thousand joules or so. In contrast, a liter of gasoline stores about 10 MJ as burned in a typical engine.

Electrical energy storage will be difficult for years to come. We see electrical energy in dc batteries or ac line supplies, single-phase circuits or three-phase circuits, 5 V or 3. Each of these myriad forms has its own purpose, and any applica- tion is best matched to a particular type of source. Electrical engineering differs from other engineering disciplines in part because it works with the intangibles of atomic physics.

In the strictest sense, people do not use electricity. As in Figure 1. Electrical engineering is concerned with con- version among these many forms. The goal of an energy conversion process is to best serve the needs of a consumer, while supporting highly efficient generation and transport of energy.

Consider a few subdisciplines of electrical engineering, with their conversion roles:. The device here, rated at p F at V, can keep a 60 W light bulb burning for only 3. Electromechanics engineers consider conversions between mechanical and electrical en- ergy forms. There are many other examples, but a basic issue has been left out: What about con- version, with emphasis on energy flow, among the various forms of electrical sources?

This is the framework of power electronics. Power electronics engineers design circuits to con- vert electrical energy among its many useful forms. Circuits Magnetics Power. This suggests that power electronics is one of the broadest subdisciplines of electrical engineering. Many students find that the study of power electronics shows them how electrical engineering fits together as a cohesive discipline. It is helpful to have a more specific definition.

Definition:Power electronics involves the stud? These circuits handle power flow at levels niuch higher than the individual device ratings. As shown in Figure 1. Although power electronics stands distinct from other electronics areas, most students and engineers have some familiarity with a few of the major applications.

Rectifiers, or cir- cuits for ac to dc conversion, are well-known examples of energy conversion circuits. In- verters, or dc to ac converter circuits, have been important for nearly a century.

Since the s, new semiconductor technologies have dramatically broadened practical possibilities for conversion circuits. A universal characteristic of power electronic circuits is that they manage the flow of electrical energy between some sort of source and a load.

The parts in a circuit must direct electrical flows, not impede them. Small components able to manipu- late heavy energy flows are of interest, analogous to valves in a plumbing system.

Let us consider some examples in an attempt to better understand the definition. Motto, ed. PA: Westinghouse, In North America, a typical stereo receiver converts 60 Hz ac energy and very low-power FM electromagnetic signals into substantial power levels at au- dio frequency. Is this power electronics? Maybe, but most amplifier circuits do not really handle high relative energy levels, and the most common types are not usually considered examples of power electronics.

A com- mercial W amplifier usually is designed with transistors big enough to dissipate the full W. The devices are used primarily to reconstruct the audio information rather than to manipulate energy flows.

In this situation, the ratio of energy handled to the device energy consumption is about 1 : 1. On the other hand, more specialized power electronics amplifiers do exist.

They are common in portable communications products, automotive systems, and telephone prod- ucts. This device is specified for peak reverse voltage of V, average forward current of 1 A, and power dissipation of 1 W. Is this a power electronic circuit?

The diode is rated for 1 W, yet is controlling W at the circuit output. The cir- cuit controls more than times as much energy as its devices consume. Rectifiers are clas- sical examples of power electronic circuits.

This device has a rated collector-emitter breakdown voltage of 30 V, a maximum collector current of 0. In a conventional analog circuit, it usually handles energy within its 0. In principle, the device can manipulate the flow of 0. Its manufacturer reports that it has a maximum continuous drain current rating of 15 A, maxi- mum drain-source breakdown voltage of V, and rated power dissipation of W. This transistor is rated for W, yet it can control the flow in a 6 kW circuit. Several manufacturers have developed power electronic controllers for domestic refrigera- tors, air conditioners, and even electric vehicles based on this device and its relatives.

Power electronics designers tend to look mainly at voltage and current ratings of a de- vice. Semiconductors of modest size can handle the energy levels in a typical home or com- mercial establishment. Semiconductor circuits for lighting, industrial motors, and even lo- comotives are in regular use.

High-power applications lead to some interesting issues. For example, in an inverter, the semiconductors often manipulate 20 times their rated power or more.

A small design er- ror or minor change could alter this somewhat, perhaps to a factor of This small change might put large additional stresses on the devices, leading to quick and catastrophic failure.

The associated excitement leads to a black magic view of the subject. Many engineers find out the hard way that power semiconductors make fast, but expensive, fuses. In the s, two major inventions determined the course of electric power systems. George Stanley built a practical transformer, and so allowed convenient conversion among various voltage levels for ac. Nikola Tesla invented the polyphase ac system, and with it showed an easy method for converting electrical energy into mechanical energy.

The advantages of low- frequency ac were compelling to designers as early as the s. Such systems form the ba- sis of power systems worldwide. However, many applications require direct current for proper operation. Electrochem- ical processes and most electronic circuits are among these. Until recently, dc motors were the choice for motion control applications. Rectification has become a more acute is- sue with the rise of electronics and computers. A personal computer often uses dc power at five or more different voltages, ranging from the internal 3 V battery for the real-time clock to 15 kV or more for the accelerating voltage in the cathode-ray tube display.

The next gen- eration may well see a revolution in superconducting materials, which will bring new con- version requirements.

Modem conversion needs reach well beyond rectifiers, and include:. A typical system not only needs multiple levels, but it often requires them to be mutually isolated so that their loads remain separate.

Rectification is one example e. An- other example is conversion between the 50 Hz system used in about half the world and the 60 Hz system used in the other half.

Mobile systems such as aircraft often use higher frequencies. Much higher frequencies are used for induction heating. Waveshape conversion square, sine, triangle, others. Sinusoidal waveforms for power minimize interference with frequency-multiplexed communication systems. They have other advantages in steady-state ac systems.

However, sine waves are not always best for power conversion or motors. Square waves are better for rectification. Triangle or trape- zoid waves are used in some motors. Single-phase ac power is by far the most widely available form of electrical energy. However, polyphase sources are by far the best form when energy is to be converted and transported. This type of conversion is important for introducing speed control and motor efficiency improvements into household appliances, for instance.

How do we accomplish these conversions? Originally, the straightforward way was to link a motor and generator on the same mechanical shaft, as in Figure 1. For example, an ac motor powered with ac electricity could drive a dc generator and thus perform ac to dc conversion. This process converts electricity to mechanical form along the way. This method sometimes still applies when power levels are very high beyond 1 MW or so , provided that the desired frequencies match available motors and generators.

Commercial machines are generally rated for dc, for 50 Hz, and for 60 Hz. There are a few electric railway systems rated for lower frequencies such as Some of the difficulties with this process of electromechanical conversion include:.

Limited conversion ranges and functions. Slow response times and limited control capability. In the past, the distinction was made between rotating converters based on machines, and static converters based on electronic circuits.

The term static power conversion has given way to the more general term power. The general nature of the conversion issues at hand can be summarized as follows:. Electricity must always be converted back and forth to the energy forms of interest to people.

Electrical engineers are in the business of energy conversion. Whether the issue involves information processing, motors, communication systems, remote sensing, or device fab- rication, electrical energy is the means to an end. Electricity is easy to control. A light switch, a volume knob, or a cathode ray tube ma- nipulate electrons with speed and precision.

Electrical supplies are needed in a variety of subtly different forms: ac, dc, high or low voltage, high or low current, and so on. Some applications of electricity are not compatible. Voltage transformation with magnetic transformers requires ac. Many chemical processes require dc. Ac motors operate at speeds that depend on the source frequency. Dc motors have speeds that can be adjusted as a function of voltage or current. Conversion of electricity among its various forms is important for a wide range of appli- cations.

Compact electronic components with adequate ratings are available, so that electronic al- ternatives to motor-generator sets can be built. While rectification has always been a key issue, there are many possible conversion objec- tives. The technological significance of many of these is growing as new applications be- come available. In many ways, the search since the s for better rectifier methods has grown into the en- tire field of power electronics. The basic form of the diode rectifier circuit was discussed in the nineteenth century, and the modem 50 kW rectifier in Figure 1.

What makes the early idea significant is the recognition that the underlying process is fundamentally nonlinear, and cannot be done with any combination of linear circuit elements such as resistors, capacitors, and inductors.

One familiar nonlinear device is a rectifying diode-an element that conducts differ- ently depending on the direction of current flow. While the silicon P-N junction diode is the most common example today, many other technologies yield a rectifying two-terminal element. One early example is the selenium diode, used by C. Fritts in a rectifier circuit as early as The development of the vacuum tube diode about twenty years later was essential to practical applications, but it is interesting that semiconductor rectifiers existed well before the invention of vacuum tubes.

The vacuum diode is limited in fundamental ways by the low current density possible in a vacuum system. A major improvement came when mercury was included in rectifier tubes. The mercury arc tube opened the way to multimegawatt power levels, even at volt- ages as low as a few hundred volts.

A paper by Charles Proteus Steinmetz considered the performance of mercury tubes for rectification. The waveforms in that paper can easily be duplicated in modern rectifier systems, and represent a broad selection of the possibili- ties of power rectification. A typical rectifier system, dating from the s, used mercury arc tubes to convert power from a 50 Hz V bus into V dc for a railway locomotive. Arc tubes are still used in certain specialized circumstances, such as rectification beyond 1 MV.

Since before the invention of the transistor, semiconductor diodes have dominated at all but the highest power levels. By the late s, single devices formed from sele- nium, copper oxide, and other nonlinear materials were manufactured commercially. The P-N junction diode appeared late in the s, and now is the dominant technology, although Schottky barrier diodes offer an alternative in many low-voltage situations.

Devices with ratings up to about 3 A and V are manufactured in huge lots. Diodes rated at more than 15 kV are readily available, and currents up to about A also can be achieved although not both simultaneously. One figure of merit is the power handling rating-the product of voltage and current ratings. Individual diodes exist with power handling capabil- ities above 36 MW. The fabrication methods for diodes have evolved rapidly. Today, hundreds of diodes with power handling ratings up to perhaps W each can be fabricated on a single silicon wafer.

The highest power devices use the opposite method: Individual diodes formed from complete single wafers are available today, even for 20 cm wafers and larger. One of the biggest challenges with large single devices is packaging: Making a A connection to a thin, brittle disk 20 cm across is a formidable task.

Complementing the packaging challenge is the challenge to find improved materials for higher power handling. Germanium is sometimes used, but it is more sensitive to high tem- peratures than silicon. Gallium arsenide power rectifiers have entered the commercial arena, and other compound materials are being examined for power rectifiers. Silicon carbide and even diamond film promise new opportunities to reach extreme power levels during the com- ing decades.

In many cases, the distinction between a rectifier and an inverter is artificial: In a rectifier, energy flows from an ac source to a dc load. In an inverter, the flow is from a dc source to an ac load. An inverter thus has much the same function as a rectifier, except for the direc- tion of energy flow. Such a circuit provides dual rectifier and inverter operation. The example in Figure 1. Although a dual use rectifier and inverter circuit is possible in principle, the rectifier diode does not support such a circuit.

A diode, as a true two-terminal element, is a passive device. This means that its behavior is determined solely by terminal conditions, and there is no direct opportunity for adjustment or other control. One of the most important power electronic devices, the silicon-controlled rectifier or SCR, addresses this need for control.

The SCR, introduced in , provides the function of a diode with the addition of a third terminal for control. The conventional SCR will not con- duct unless a signal is applied to this control terminal, or gate.

Once a gate signal is present, the device operates more or less as a conventional diode. In this way, the gate permits ad- justment of the conduction behavior, and leads to the concept of an adjustable diode. The SCR was not the first technology to provide controlled rectifier function. By the s, passive circuit methods were combined with vacuum diodes to create similar func- tions. Grid control was used with mercury arc tubes to provide controlled rectification by the s.

The cycloconverter-a complicated controlled rectifier adapted for ac-ac con- version-was introduced in about Photographer: Peter S. The device brought about a revolution in electronic power conversion. Such familiar applications as variable- speed kitchen appliances and lamp dimmers rely on the SCR and its relatives for control.

It is sometimes said that power electronics began when the SCR was introduced. Once a controlled rectifier can be built, the step to inverters is a small one.

Inverters are the critical conversion method for most alternative energy resources. Sources as diverse as wind energy, solar panels, battery banks, and superconducting magnetic energy storage SMES rely on inverter circuits to transfer their energy to an ac power grid. The SCR re- mains crucial for these kinds of systems. Very high power levels have always been an important application for inverters and controlled rectifiers. This is because dc power is the most economical form for transmission of energy over very long distances.

Beyond about km or so, wavelength effects begin to bring trouble to ac power networks. Resonances and reflections can affect behavior or cre- ate failures. Dc power avoids these fundamental problems, and high-voltage dc HVDC power transmission remains an important application.

Pacific coast is rated at up to kV and MW. These levels are far beyond the capacity of any individual device, and large series and parallel combinations of devices must be used to provide diode or controlled rectifier functions. In this particular case, each line terminal can act either as a rectifier or inverter there are two sets of devices at each end so that the line power can be adjusted for seasonal changes in energy flow. Some installations elsewhere in the world sup- port only unidirectional power flow.

Two of the fastest-growing inverter applications are not as well served by the SCR. These are circuits for independent backup power and circuits for control of ac motors.

Two small modem commercial units are shown in Figure 1. The most straightforward inverter cir- cuits use timing information from the ac voltage source to control their operation. Backup circuits and motor controllers do not have access to this qort of time reference information. Without such timing information, inverter control can be complicated. Motor control and backup applications were difficult to build from electronic circuits until relatively recently.

One early ex'ample was the Stir-Lec I, an experimental electric vehicle built by General Mo- tors in This car used SCRs in an innovative but Complicated arrangement to convert dc power from batteries for an ac motor.

Both backup power and ac motor control systems were considered to be classical ap- plications of motor-generator sets prior to the semiconductor revolution. Diesel-driven gen- erator systems remain the standard choice for large backup power sources. Battery backup is common in dc applications, such as telephone networks and communication equipment.

Batteries are becoming more common in small backup applications. Equipment rated for the kW range is now readily available. The growth in low-power battery-backup inverters can be attributed in part to devel- opments in transistor technology. Toggle navigation. Main Elements of Power Electronics.

Power electronics is an enabling technology for almost all electrical applications. The field is growing rapidly because electrical devices need electronic circuits to process their energy. Elements of Power Electronics, the first undergraduate book to discuss this subject in a conceptual framework, provides comprehensive coverage of power electronics at a level suitable for undergraduate student engineers, students in advanced degree programs, and novices in the field.

It aims to establish a fundamental engineering basis for power electronics analysis, design, and implementation, offering broad and in-depth coverage of basic material. The texts unifying framework includes the physical implications of circuit laws, switching circuit analysis, and the basis for converter operation and control. Dc-dc, ac-dc, dc-ac, and ac-ac conversion tasks are examined and principles of resonant converters and discontinuous converters are discussed.

Models for real devices and components are developed in depth, including models for real capacitors, inductors, wire connections, and power semiconductors. Magnetic device design is introduced, and thermal management and drivers for power semiconductors are addressed. Control system aspects of converters are discussed, and both small-signal and geometric controls are explored. Many examples show ways to use modern computer tools such as Mathcad, Matlab, and Mathematica to aid in the analysis and design of conversion circuits.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying. ISBN I 1. Power electronics. K74 62 1. Power electronics is one of the broadest growth areas in electrical technology. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising.

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