ffirs 30 August 2011; 14:59:40 Power Electronics A First Course ffirs 30 August 2011; 14:59:40 ffirs 30 August 2011; 14:59:40 Power Electronics A First Course NED MOHAN Oscar A. Schott Professor of Power Electronics and Systems Department of Electrical and Computer Engineering University of Minnesota Minneapolis, MN USA John Wiley & Sons, Inc. ffirs 30 August 2011; 14:59:40 VP & PUBLISHER: Don Fowley EDITOR: Dan Sayre PROJECT EDITOR: Nithyanand Rao EDITORIAL ASSISTANT: Charlotte Cerf MARKETING MANAGER: Christopher Ruel MARKETING ASSISTANT: Ashley Tomeck DESIGNER: James O’Shea SENIOR PRODUCTION MANAGER: Janis Soo SENIOR PRODUCTION EDITOR: Joyce Poh PSpice is a registered trademark of the OrCAD Corporation. SIMULINK is a registerd trademark of The Mathworks, Inc. This book was set in 10/12 TimesNewRoman by MPS Limited, a Macmillan Company, Chennai and printed and bound by Hamilton Printing. The cover was printed by Hamilton Printing. This book is printed on acid free paper. 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Upon completion of the review period, please return the evaluation copy to Wiley. Return instructions and a free of charge return mailing label are available at www.wiley.com/go/returnlabel. If you have chosen to adopt this textbook for use in your course, please accept this book as your complimentary desk copy. Outside of the United States, please contact your local sales representative. Library of Congress Cataloging-in-Publication Data Mohan, Ned. Power electronics : a first course / Ned Mohan. p. cm. Includes bibliographical references and index. ISBN 978-1-118-07480-0 (hardback : acid free paper) 1. Power electronics—Textbooks. 2. Electric current converters—Textbooks. I. Title. TK7881.15.M638 2012 621.3107—dc23 2011029128 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 ffirs 30 August 2011; 14:59:40 To my family and friends ffirs 30 August 2011; 14:59:40 ffirs 30 August 2011; 14:59:40 CONTENTS PREFACE xiii CHAPTER 1 POWER ELECTRONICS: AN ENABLING TECHNOLOGY 1 1.1 Introduction to Power Electronics 1 1.2 Applications and the Role of Power Electronics 2 1.3 Energy and the Environment: Role of Power Electronics in Providing Sustainable Electric Energy 4 1.4 Need for High Efficiency and High Power Density 8 1.5 Structure of Power Electronics Interface 9 1.6 Voltage-Link-Structure 11 1.7 Recent and Potential Advancements 16 References 16 Problems 17 CHAPTER 2 DESIGN OF SWITCHING POWER-POLES 21 2.1 Power Transistors and Power Diodes 21 2.2 Selection of Power Transistors 22 2.3 Selection of Power Diodes 24 2.4 Switching Characteristics and Power Losses in Power-Poles 25 2.5 Justifying Switches and Diodes as Ideal 30 2.6 Design Considerations 30 2.7 The PWM IC 33 References 33 Problems 34 Appendix 2A Diode Reverse-Recovery and Power Losses 35 CHAPTER 3 SWITCH-MODE DC-DC CONVERTERS: SWITCHING ANALYSIS, TOPOLOGY SELECTION AND DESIGN 38 3.1 DC-DC Converters 38 3.2 Switching Power-Pole in DC Steady State 38 3.3 Simplifying Assumptions 42 3.4 Common Operating Principles 43 ftoc 30 August 2011; 15:0:33 vii 3.5 Buck Converter Switching Analysis in DC Steady State 43 3.6 Boost Converter Switching Analysis in DC Steady State 45 3.7 Buck-Boost Converter Analysis in DC Steady State 50 3.8 Topology Selection 56 3.9 Worst-Case Design 57 3.10 Synchronous-Rectified Buck Converter for Very Low Output Voltages 57 3.11 Interleaving of Converters 58 3.12 Regulation of DC-DC Converters by PWM 58 3.13 Dynamic Average Representation of Converters in CCM 59 3.14 Bi-Directional Switching Power-Pole 61 3.15 Discontinuous-Conduction Mode (DCM) 62 References 68 Problems 68 CHAPTER 4 DESIGNING FEEDBACK CONTROLLERS IN SWITCH-MODE DC POWER SUPPLIES 74 4.1 Introduction and Objectives of Feedback Control 74 4.2 Review of Linear Control Theory 75 4.3 Linearization of Various Transfer Function Blocks 77 4.4 Feedback Controller Design in Voltage-Mode Control 83 4.5 Peak-Current Mode Control 86 4.6 Feedback Controller Design in DCM 91 References 93 Problems 93 Appendix 4A Bode Plots of Transfer Functions with Poles and Zeros 94 Appendix 4B Transfer Functions in Continuous Conduction Mode (CCM) (on accompanying website) 97 Appendix 4C Derivation of Parameters of the Controller Transfer Functions (on accompanying website: www.wiley.com/college/mohan) 97 CHAPTER 5 RECTIFICATION OF UTILITY INPUT USING DIODE RECTIFIERS 98 5.1 Introduction 98 5.2 Distortion and Power Factor 99 5.3 Classifying the “Front-End” of Power Electronic Systems 107 5.4 Diode-Rectifier Bridge “Front-Ends” 107 ftoc 30 August 2011; 15:0:33 viii Contents 5.5 Means to Avoid Transient Inrush Currents at Starting 113 5.6 Front-Ends with Bi-Directional Power Flow 114 Reference 114 Problems 114 CHAPTER 6 POWER-FACTOR-CORRECTION (PFC) CIRCUITS AND DESIGNING THE FEEDBACK CONTROLLER 116 6.1 Introduction 116 6.2 Operating Principle of Single-Phase PFCs 116 6.3 Control of PFCs 119 6.4 Designing the Inner Average-Current-Control Loop 120 6.5 Designing the Outer Voltage-Control Loop 122 6.6 Example of Single-Phase PFC Systems 124 6.7 Simulation Results 125 6.8 Feedforward of the Input Voltage 125 6.9 Other Control Methods for PFCs 125 References 127 Problems 127 Appendix 6A Proving that ^Is3 ^IL2 ¼ 1 2 128 Appendix 6B Proving that ~vd ~iL ðsÞ ¼ 1 2 ^Vs Vd R=2 1 þ sðR=2ÞC 129 CHAPTER 7 MAGNETIC CIRCUIT CONCEPTS 130 7.1 Ampere-Turns and Flux 130 7.2 Inductance L 131 7.3 Faraday’s Law: Induced Voltage in a Coil Due to Time-Rate of Change of Flux Linkage 133 7.4 Leakage and Magnetizing Inductances 134 7.5 Transformers 136 Reference 139 Problems 139 CHAPTER 8 SWITCH-MODE DC POWER SUPPLIES 141 8.1 Applications of Switch-Mode DC Power Supplies 141 8.2 Need for Electrical Isolation 142 8.3 Classification of Transformer-Isolated DC-DC Converters 142 8.4 Flyback Converters 142 8.5 Forward Converters 145 8.6 Full-Bridge Converters 148 ftoc 30 August 2011; 15:0:33 Contents ix 8.7 Half-Bridge and Push-Pull Converters 152 8.8 Practical Considerations 152 Reference 152 Problems 153 CHAPTER 9 DESIGN OF HIGH-FREQUENCY INDUCTORS AND TRANSFORMERS 155 9.1 Introduction 155 9.2 Basics of Magnetic Design 155 9.3 Inductor and Transformer Construction 156 9.4 Area-Product Method 156 9.5 Design Example of an Inductor 159 9.6 Design Example of a Transformer for a Forward Converter 161 9.7 Thermal Considerations 161 References 161 Problems 162 CHAPTER 10 SOFT-SWITCHING IN DC-DC CONVERTERS AND CONVERTERS FOR INDUCTION HEATING AND COMPACT FLUORESCENT LAMPS 163 10.1 Introduction 163 10.2 Hard-Switching in Switching Power-Poles 163 10.3 Soft-Switching in Switching Power-Poles 165 10.4 Inverters for Induction Heating and Compact Fluorescent Lamps 169 References 170 Problems 170 CHAPTER 11 APPLICATIONS OF SWITCH-MODE POWER ELECTRONICS IN MOTOR DRIVES, UNINTERRUPTIBLE POWER SUPPLIES, AND POWER SYSTEMS 172 11.1 Introduction 172 11.2 Electric Motor Drives 172 11.3 Uninterruptible Power Supplies (UPS) 184 11.4 Utility Applications of Switch-Mode Power Electronics 185 References 187 Problems 187 ftoc 30 August 2011; 15:0:33 x Contents CHAPTER 12 SYNTHESIS OF DC AND LOW-FREQUENCY SINUSOIDAL AC VOLTAGES FOR MOTOR DRIVES, UPS AND POWER SYSTEMS APPLICATIONS 189 12.1 Introduction 189 12.2 Bi-Directional Switching Power-Pole as the Building-Block 190 12.3 Converters for DC Motor Drives (2Vd , vo , Vd) 194 12.4 Synthesis of Low-Frequency AC 200 12.5 Single-Phase Inverters 201 12.6 Three-Phase Inverters 204 12.7 Multilevel Inverters 212 12.8 Converters for Bi-Directional Power Flow 213 12.9 Matrix Converters (Direct Link System) 214 References 221 Problems 221 Appendix 12A Space Vector Pulse-Width-Modulation (SV-PWM) 223 CHAPTER 13 THYRISTOR CONVERTERS 230 13.1 Introduction 230 13.2 Thyristors (SCRs) 230 13.3 Single-Phase, Phase-Controlled Thyristor Converters 232 13.4 Three-Phase, Full-Bridge Thyristor Converters 237 13.5 Current-Link Systems 243 Reference 244 Problems 245 CHAPTER 14 UTILITY APPLICATIONS OF POWER ELECTRONICS 247 14.1 Introduction 247 14.2 Power Semiconductor Devices and Their Capabilities 248 14.3 Categorizing Power Electronic Systems 248 14.4 Distributed Generation (DG) Applications 250 14.5 Power Electronic Loads 255 14.6 Power Quality Solutions 255 14.7 Transmission and Distribution (T&D) Applications 257 References 261 Problems 261 ftoc 30 August 2011; 15:0:33 Contents xi ftoc 30 August 2011; 15:0:33 PREFACE Role of Power Electronics in Providing Sustainable Electric Energy As discussed in the introductory chapter of this textbook, power electronics is an enabling technology for powering information technology and making factory automation feasible. In addition, power electronics has a crucial role to play in providing sustainable electric energy. Most scientists now believe that carbon-based fuels for energy production con- tribute to climate change, which is a serious threat facing our civilization. In the United States, the Department of Energy reports that approximately 40% of all the energy consumed is first converted into electricity. Potentially, use of electric and plug-in hybrid cars, high speed rails, and so on may increase this to even 60%. Therefore, it is essential that we generate electricity from renewable sources such as wind and solar, which at present represent only slightly over 4%, build the next-generation smarter and robust grid to utilize renewable resources often in remote locations, and use electricity in more energy-efficient ways. Undoubtedly, using electricity efficiently and generating it from renewable sources are the twin pillars of sustainability, and as described in this textbook, power electronic systems are a key to them both! This textbook focuses on Power Electronic Systems as one of the topics in an integrated Electric Energy Systems curriculum consisting of Power Electronics, Power Systems and Electric Machines and Drives. This textbook follows a top-down systems- level approach to Power Electronics to highlight interrelationships between these sub- fields within this curriculum, and is intended to cover both the fundamentals and practical design in a single-semester course. This textbook follows a building-block approach to power electronics that allows an in-depth discussion of several important topics that are left out in a conventional course, for example, designing feedback control, power-factor-correction circuits, soft- switching, and Space-Vector PWM, which is a PWM technique, far superior to Sine- PWM, to name a few. Topics in this book are carefully sequenced to maintain continuity and student interest throughout the course. In a fast-paced course with proper student background, this book can be covered from front-to-back in one semester. However, the material is arranged in such a way that an instructor, to accommodate the students’ background, can either omit an entire topic or cover it quickly to provide just an overview using the accompanying slides, without interrupting the flow. fpref 30 August 2011; 9:40:5 xiii