Rashid Power Electronics Handbook

3. Auflage 2011
ISBN: 978-0-12-382037-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 1362 Seiten

Power electronics, which is a rapidly growing area in terms of research and applications, uses modern electronics technology to convert electric power from one form to another, such as ac-dc, dc-dc, dc-ac, and ac-ac with a variable output magnitude and frequency. It has many applications in our every day life such as air-conditioners, electric cars, sub-way trains, motor drives, renewable energy sources and power supplies for computers. This book covers all aspects of switching devices, converter circuit topologies, control techniques, analytical methods and some examples of their applications. Designed to appeal to a new generation of engineering professionals, Power Electronics Handbook, 3rd Edition features four new chapters covering renewable energy, energy transmission, energy storage, as well as an introduction to Distributed and Cogeneration (DCG) technology, including gas turbines, gensets, microturbines, wind turbines, variable speed generators, photovoltaics and fuel cells, has been gaining momentum for quite some time now.smart grid technology. With this book readers should be able to provide technical design leadership on assigned power electronics design projects and lead the design from the concept to production involving significant scope and complexity. - Contains 45 chapters covering all aspects of power electronics and its applications - Three new chapters now including coverage Energy Sources, Energy Storage and Electric Power Transmission - Contributions from more than fifty leading experts spanning twelve different countries

Autoren/Hrsg.

Rashid, Muhammad H.

Leseproben

1

Introduction

Philip T. Krein, Ph.D.

Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, USA

1.1 Power Electronics Defined

1.2 Key Characteristics

1.2.1 The Efficiency Objective –The Switch

1.2.2 The Reliability Objective –Simplicity and Integration

1.3 Trends in Power Supplies

1.4 Conversion Examples

1.4.1 Single-Switch Circuits

1.4.2 The Method of Energy Balance

1.5 Tools for Analysis and Design

1.5.1 The Switch Matrix

1.5.2 Implications of Kirchhoff's Voltage and Current Laws

1.5.3 Resolving the Hardware Problem –Semiconductor Devices

1.5.4 Resolving the Software Problem –Switching Functions

1.5.5 Resolving the Interface Problem –Lossless Filter Design

1.6 Sample Applications

1.7 Summary

    References

1.1 Power Electronics Defined1

It has been said that people do not use electricity, but rather they use communication, light, mechanical work, entertainment, and all the tangible benefits of energy and electronics. In this sense, electrical engineering as a discipline is much involved in energy conversion and information. In the general world of electronics engineering, the circuits engineers design and use are intended to convert information. This is true of both analog and digital circuit design. In radio-frequency applications, energy and information are on more equal footing, but the main function of any circuit is information transfer.

What about the conversion and control of electrical energy itself? Energy is a critical need in every human endeavor. The capabilities and flexibility of modern electronics must be brought to bear to meet the challenges of reliable, efficient energy. It is essential to consider how electronic circuits and systems can be applied to the challenges of energy conversion and management. This is the framework of , a discipline defined in terms of , and More specifically,

DEFINITION involves the study of electronic circuits intended to control the flow of electrical energy. These circuits handle power flow at levels much higher than the individual device ratings.

Rectifiers are probably the most familiar examples of circuits that meet this definition. Inverters (a general term for dc–ac converters) and dc–dc converters for power supplies are also common applications. As shown in Fig. 1.1, power electronics represents a median point at which the topics of energy systems, electronics, and control converge and combine [1]. Any useful circuit design for an energy application must address issues of both devices and control, as well as of the energy itself. Among the unique aspects of power electronics are its emphasis on large semiconductor devices, the application of magnetic devices for energy storage, special control methods that must be applied to nonlinear systems, and its fundamental place as a central component of today's energy systems and alternative resources. In any study of electrical engineering, power electronics must be placed on a level with digital, analog, and radio-frequency electronics to reflect the distinctive design methods and unique challenges.

FIGURE 1.1 Control, energy, and power electronics are interrelated.

Applications of power electronics are expanding exponentially. It is not possible to build practical computers, cell phones, personal data devices, cars, airplanes, industrial processes, and a host of other everyday products without power electronics. Alternative energy systems such as wind generators, solar power, fuel cells, and others require power electronics to function. Technology advances such as electric and hybrid vehicles, laptop computers, microwave ovens, flat-panel displays, LED lighting, and hundreds of other innovations were not possible until advances in power electronics enabled their implementation. Although no one can predict the future, it is certain that power electronics will be at the heart of fundamental energy innovations.

The history of power electronics [2–5] has been closely allied with advances in electronic devices that provide the capability to handle high power levels. Since about 1990, devices have become so capable that a transition from a “device-driven” field to an “applications-driven” field continues. This transition has been based on two factors: (1) advanced semiconductors with suitable power ratings exist for almost every application of wide interest, and (2) the general push toward miniaturization is bringing advanced power electronics into a growing variety of products. Although the devices continue to improve, their development now tends to follow innovative applications.

1.2 Key Characteristics

All power electronic circuits manage the flow of electrical energy between an electrical source and a load. The parts in a circuit must direct electrical flows, not impede them. A general power conversion system is shown in Fig. 1.2. The function of the power converter in the middle is to control the energy flow between a source and a load. For our purposes, the power converter will be implemented with a power electronic circuit. Because a power converter appears between a source and a load, any energy used within the converter is lost to the overall system. A crucial point emerges: to build a power converter, we should consider only lossless components. A realistic converter design must approach 100% efficiency.

FIGURE 1.2 General system for electric power conversion. (From [2], © 1998, Oxford University Press, Inc.; used by permission.)

A power converter connected between a source and a load also affects system reliability. If the energy source is perfectly reliable (it is available all the time), then a failure in the converter affects the user (the load) just as if the energy source had failed. An unreliable power converter creates an unreliable system. To put this in perspective, consider that a typical American household loses electric power only a few minutes a year. Energy is available 99.999% of the time. A converter must be better than this to prevent system degradation. An ideal converter implementation will not suffer any failures over its application lifetime. Extreme high reliability can be a more difficult objective than high efficiency.

1.2.1 The Efficiency Objective –The Switch

A circuit element as simple as a light switch reminds us that the extreme requirements in power electronics are not especially novel. Ideally, when a switch is on, it has zero voltage drop and will carry any current imposed on it. When a switch is off, it blocks the flow of current regardless of the voltage across it. The , the product of the switch voltage and current, is identically zero at all times. A switch therefore controls energy flow with no loss. In addition, reliability is also high. Household light switches perform over decades of use and perhaps 100,000 operations. Unfortunately, a mechanical light switch does not meet all practical needs. A switch in a power supply may function 100,000 times each second. Even the best mechanical switch will not last beyond a few million cycles. Semiconductor switches (without this limitation) are the devices of choice in power converters.

A circuit built from ideal switches will be lossless. As a result, switches are the main components of power converters, and many people equate power electronics with the study of switching power converters. Magnetic transformers and lossless storage elements such as capacitors and inductors are also valid components for use in power converters. The complete concept, shown in Fig. 1.3, illustrates a Such a system consists of an electrical energy source, an electrical load, a , and a control function.

FIGURE 1.3 A basic power electronic system. (From [2], © 1998, Oxford University Press, Inc.; used by permission.)

The power electronic circuit contains switches, lossless energy storage elements, and magnetic transformers. The controls take information from the source, the load, and the designer, and then determine how the switches operate to achieve the desired conversion. The controls are built up with low-power analog and digital electronics.

Switching devices are selected based on their rating –the product of their voltage and current ratings –rather than on power dissipation ratings. This is in contrast to other applications of electronics, in which power dissipation ratings dominate. For instance, a typical stereo receiver performs a conversion from ac line input to audio output. Most audio amplifiers do not use the techniques of power electronics, and the semiconductor devices do not act as switches. A commercial 100-W amplifier is usually designed with transistors big enough to dissipate the full 100W. The semiconductor devices are used primarily to reconstruct the audio information rather than to manipulate the energy flows. The sacrifice in...