Page 18 - Rashid, Power Electronics Handbook

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Introduction

Dr. Philip Krein 1.1 Power Electronics De®ned ..................................................................... 1
Department of Electrical and 1.2 Key Characteristics ............................................................................... 2
Computer Engineering 1.2.1 The Ef®ciency Objective: The Switch 1.2.2 The Reliability Objective: Simplicity and
University of Illinois at
Urbana-Champaign Integration
341 William L. Everitt 1.3 Trends in Power Supplies....................................................................... 3
Laboratory 1.4 Conversion Examples............................................................................ 4
1406 West Green Street 1.4.1 Single-switch Circuits 1.4.2 The Method of Energy Balance
Urbana, Illinois 61801, USA
1.5 Tools for Analysis and Design ................................................................ 7
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 Summary ............................................................................................ 12
References ........................................................................................... 12

1.1 Power Electronics Defined 1 DEFINITION: Power electronics involves the study of
electronic circuits intended to control the ¯ow of elec-
It has been said that people do not use electricity, but rather trical energy. These circuits handle power ¯ow at levels
they use communication, light, mechanical work, entertain- much higher than the individual device ratings.
ment, and all the tangible bene®ts of both energy and Recti®ers are probably the most familiar example of circuits
electronics. In this sense, electrical engineering is a discipline that meet this de®nition. Inverters (a general term for dc-ac
very much involved in energy conversion and information. In converters) and dc-dc converters for power supplies are also
the general world of electronics engineering, the circuits common applications. As shown in Fig. 1.1, power electronics
engineers design and use are intended to convert information, represents a median point at which the topics of energy
with energy merely a secondary consideration in most cases. systems, electronics, and control converge and combine [1].
This is true of both analog and digital circuit design. In radio Any useful circuit design for the control of power must
frequency applications, energy and information are sometimes
address issues of both devices and control, as well as of the
on a more equal footing, but the main function of any circuit
energy itself. Among the unique aspects of power electronics
is that of information transfer.
are its emphasis on large semiconductor devices, the applica-
What about the conversion and control of electrical energy
tion of magnetic devices for energy storage, and special control
itself? Electrical energy sources are varied and of many types.
methods that must be applied to nonlinear systems. In any
It is natural, then, to consider how electronic circuits and
study of electrical engineering, power electronics must be
systems can be applied to the challenges of energy conversion
placed on a level with digital, analog, and radio-frequency
and management. This is the framework of power electronics,a
electronics if we are to re¯ect its distinctive design methods
discipline that is de®ned in terms of electrical energy conver-
and unique challenges.
sion, applications, and electronic devices. More speci®cally, The history of power electronics [2,3,4,5] has been closely
allied with advances in electronic devices that provide the
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Portions of this chapter are from P. T. Krein, Elements of Power
Electronics. New York: Oxford University Press, 1998. Copyright # 1998, capability to handle high-power levels. Only in the past decade
Oxford University Press Inc. Used by permission. has a transition been made from a ‘‘device-driven'' ®eld to an
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Copyright # 2001 by Academic Press.
All rights of reproduction in any form reserved.