Power Electronics Semiconductor Switches

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1 Power Electronics Semiconductor Switches

2 Power Electronics Semiconductor Switches R.S. Ramshaw Department of Electrical and Computer Engineering University of Waterloo Ontario Canada SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

3 ISBN ISBN (ebook) DOI / First edition R.S. Rarnshaw Originally published by Chapman & Hall in 1993 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the OK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied. with regard to the accuracy of the information conlained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication data available Printed on permanent acid-free text paper, manufactured in accordance with the proposed ANSIINISO Z X and ANSI Z

4 CONTENTS PREFACE xiii Chapter 1 POWER CONDITIONING Introduction Power Electronics Power Modulation DC Supplies to a Load AC Supplies to a Load Waveform Distortion Average Values RMS Values Form Factor Harmonics Total Harmonic Distortion (THD) Average Power Power Semiconductor Switches Applications Summary Problems 23 Chapter 2 SWITCHES IN CIRCUITS Introduction DC to DC Conversion Buck Converter Boost Converter AC to DC Conversion Converter Performance and Operation Modes Single-phase Half-wave Converter Single-phase Bridge Converter DC to AC Conversion Centre-tapped Source Inverter Single-phase Bridge Inverter Three-phase Inverters Summary Problems Bibliography 89

5 -VI- Chapter 3 THE DIODE Introduction Diode Structure Diode I-V Characteristics Forward Bias Reverse Bias Ideal Diode Diode Models Diode Turn-on Diode Turn-off Diode Protection Overcurrent Overvoltage Transients Diode Ratings Applications and Analysis Ratings Rectification Diodes in Parallel and Series Summary Problems Bibliography 122 Chapter 4 THE BJT TRANSISTOR Introduction BJT Structure BJT I-V Characteristics Ideal Switch Nonideal Switch BlTModels BJT turn-on Turn-on Action Tum-on Losses BJT Turn-off Tum-off Losses Current Focusing BlT Power Dissipation BJT Base Drive Baker Clamp BJT Protection Overcurrent Overvoltage 153

6 -vii Safe Operating Area (SOA) Transients BJT Ratings and Applications Applications Summary Problems Bibliography Chapter 5 THE THYRISTOR 5.1. Introduction 5.2. Thyristor Structure 5.3. Thyristor Models Diode Model of the Thyristor Two-transistor Model of the Thyristor 5.4. Thyristor I-V Characteristics 5.5. Thyristor Turn-on Turn-on Losses Turn-on Circuits 5.6. Thyristor Turn-off Turn-off Circuits 5.7. Thyristor Power Dissipation 5.8. Thyristor Ratings 5.9. Thyristor Protection Main Power Circuit Gate Protection Thennal Considerations Thennal Resistance Transient Thennal Impedance Thyristors in Series and Parallel Thyristors in Series Thyristors in Parallel Summary Problems Bibliography

7 -viii - Chapter 6 THE MOSFET Introduction MOSFET Structure MOSFET I-V Characteristics MOSFET Models MOSFET Turn-on Turn-on Action Turn-on Losses MOSFET Turn-off Turn-off Losses MOSFET Gate Circuits MOSFET Protection Overvoltages Overcurrents Transients MOSFET Ratings and Applications Summary Problems Bibliography 293 Chapter 7 THEIGBT Introduction IGBT Structure IGBT I-V Characteristics IGBT Model IGBTTurn-on Turn-on Losses IGBT Turn-off Turn-off Losses IGBT Protection Overvoltages Overcurrent Transients IGBT Ratings and Applications Summary Problems Bibliography 323

8 -ix- ChapterS THETRIAC Introduction Triac Structure Triac Model Triac I-V Characteristics Triac Turn-on Turn-on Action Turn-on Losses Turn-on Circuits Triac Turn-off Triac Ratings Thermal Ratings Triac Protection Triac Applications AC-AC Conversion AC-DC Conversion Summary Problems Bibliography 353 Chapter 9 THEGTO Introduction GTO Structure G TO I-V Charac teris tics GTO Two-transistor Model GTOTurn-on GTO Turn-off GTO Gate Circuits GTO Protection GTO Ratings and Applications Summary Problems Bibliography 385

9 - x - Chapter 10 OTHER SWITCHES AND THE MCT I. Introduction The SIT I. SIT Structure SIT I-V Characteristics SIT Turn-off SIT Turn-on SIT Protection SIT Ratings and Applications The SITH 391 1O.3.I. SITH Structure SITH I-V Characteristics SITH Turn-off SITH Turn-on SITH Protection SITH Ratings and Applications Thyristors I. The ASCR TheGATI TheRCT TheMCT 397 1O.S.I. MCT Structure MCT I-V Characteristics MCTModels MCTTurn-on MCTTurn-off MCT Protection MCT Ratings and Applications Summary Problems Bibliography 409 APPENDIX 1 Rectifier Diode Data Sheets 410 APPENDIX 2 BJT Power Transistor Data Sheets 414 APPENDIX 3 Power MOSFET Data Sheets 418 APPENDIX 4 Thyristor Data Sheets 426 APPENDIX 5 IGBT Data Sheets 430 APPENDIX 6 Triac Data Sheets 434

10 -xi- APPENDIX 7 GTO Data Sheets APPENDIX 8 MeT Data Sheets APPENDIX 9 Answers to Problems APPENDIX 10 List of Symbols INDEX 454

11 PREFACE Power electronics plays a significant role in the application of electric power wherever there is a need to change voltage,.current or frequency from the standard values that are available. At the heart of power electronics is a fast acting switch that is used, not just to isolate the source from the load, but to modulate the power that reaches the load. This is an introductory text about semiconductor switches and their uses to modulate power to a form best suited to a load. Today the subject of power electronics has expanded to include not only power semiconductor devices, but also to incorporate converter topologies, analysis and simulation, control and estimation techniques and control hardware together with the attendant software. Each of these is a topic in its own right and is left for further study following this text. In the first part of the text there is a description of how power is converted from ac to dc, ac to ac, dc to dc and dc to ac forms in the terms of the periodic opening and closing of a single switch or a group of switches that are ideal That is, the basics of power conditioning are generalized. In the second part of the text, systems of supply, converter and load are described. The equations that govern the behaviour of those converters with ideal switches are formulated to provide the fundamentals of the analysis of power conditioning in basic circuits. The result is twofold. The basic responses of currents voltages and average power are determined for the input and output of the converter, starting with the simplest load and progressing to complex passive loads. Further, the performance factors that describe the goodness of power conversion are applied to each type of converter. This description is broadly based with simple analytical treatments of simple systems to show in first principles what is possible to be done with more complex switching systems. With this background to the use of semiconductor switches, the important switches are treated separately in the third and main part of the text. The purpose is to help the reader make a choice of the right switch for a particular application and to help in the use of the switches in circuits. For each switch there is a description of operation in general terms of a pn junction and charge flow under the influence of electric fields. The physics of operation is omitted, because the text is aimed at those who may have the desire to use switches in a converter. Circuit operation and switch control are the important objectives of this text. No switch is perfect. Accordingly, some attempt is made to accentuate the performance characteristics of the switch in terms of steady-state and transient operation. From this, the main forms of protection become evident. Design techniques for circuits and systems that incorporate switches are left to manufacturers' manuals. The analytical descriptions, that are given in this text, are mainly to show the principles of switch and circuit behaviour and to provide a

12 -xivbase so that manufacturers' data sheets and manuals can be used to the best effect. The best effect usually means minimum losses and waveforms as close to the ideal as possible. This book is intended as a text for readers who wish to become users of semiconductor switches and who wish to understand basics of power electronics and switch applications. It is for this reader that there are many worked examples and many more problems for practice. Hands-on experience quickly shows the fragility and limitations of power electronics circuits, just like solving problems enables rapid learning of principles and an acknowledgement of the limitations of our modelling and analytical tools. Many of the problems make use of chopper circuits to exemplify a switch's performance, because choppers provide extreme characteristics that are relatively easy to analyze. Although this book sets out to be a first course in the subject of power electronics, it does rely on the readers' familiarity with a fundamental electrical engineering course in circuit theory and its attendant mathematics. The level of analysis has increased in recent years. The knowledge of mathematics that is required has not changed much, but the complexity of the switched-circuit analysis has been extended by the availability of mathematical tools for computer aided analysis. There are software packages (MATLAB, MATHCAD etc.) available to take away the drudgery of solving a transcendental equation and to solve problems of Fourier analysis, of complex integrals or simultaneous transcendental equations that might have been left alone before. As this book is an introductory text, the bibliography given at the end of each chapter is an invitation for further reading. Acknowledgement and gratitude are due to Elizabeth Nicklin who has taken the author's scribblings and sketches and transformed them into the typeset text and figures set before you. The University of Auckland kindly provided the facilities for the preparation of the text. At the University of Auckland James Thompson was kind enough to solve many of the MATLAB problems and Grant Spencer gave his time generously to proof-read the final draft. Thanks are due to Philips Export B.V. and Harris Semiconductor for giving permission to reproduce their data sheets. Raymond Ramshaw Waterloo.

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