Power conversion and control of wind energy systems

POWER CONVERSION AND CONTROL OF WIND ENERGY SYSTEMS

IEEE Press 445 Hoes Lane Piscataway, NJ 08855 IEEE Press Editorial Board Lajos Hanzo, Editor in Chief R. Abhari J. Anderson G. W. Arnold F. Cañavero

M. El-Hawary B-M. Hammerli M. Lanzerotti D.Jacobson

O. P. Malik S. Nahavandi T. Samad G. Zobrist

Kenneth Moore, Director of IEEE Book and Information Services (BIS)

POWER CONVERSION AND CONTROL OF WIND ENERGY SYSTEMS

BinWu Yongqiang Lang Navid Zargari Samir Kouro

IEEE PRESS SERIES |

GROWER ENGINEERING

♦IEEE IEEE Press

WILEY A JOHN WILEY & SONS, INC., PUBLICATION

Copyright © 2011 by the Institute of Electrical and Electronics Engineers, Inc. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. All rights reserved. Published simultaneously in Canada. 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, recording, scanning or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representation or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 5724002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-Publication Data: Power conversion and control of wind energy systems / Bin Wu ... [et al.], p. cm. — (IEEE Press series on power engineering ; 74) Summary: "The book covers a wide range of topics on wind energy conversion and control from the electrical engineering aspect. It includes wind generators and modeling, power converters and modulation schemes, operating principle of fixed and variable speed wind turbines, advanced generator control schemes, active and reactive power controls of individual wind and is a valuable reference book for academic researchers, practicing engineers, and other professionals. The book can also be used as a textbook for graduate level and final year undergraduate-level courses"— Provided by publisher. Includes bibliographical references and index. ISBN 978-0-470-59365-3 (hardback) 1. Wind energy conversion systems. I. Wu, B. (Bin), 1957TK1541.P685 2011 621.31'2136—dc22 2010045226 Printed in the United States of America. oBook ISBN: 978-1-118-02900-8 ePDFISBN: 978-1-118-02899-5 ePub ISBN: 978-1-118-02898-8 10 9 8 7 6 5 4 3 2 1

CONTENTS

Preface List of Symbols Acronyms and Abbreviations

xi xiii xxiii

1. Introduction 1.1 Introduction 1.2 Overview of Wind Energy Conversion Systems 1.2.1 Installed Capacity and Growth Rate 1.2.2 Small and Large Wind Turbines 1.2.3 Stand-Alone and Grid-Connected Applications 1.2.4 On-Land and Offshore Applications 1.2.5 Costs of Wind Energy Conversion Systems 1.3 Wind Turbine Technology 1.3.1 Horizontal- and Vertical-Axis Wind Turbines 1.3.2 Fixed-and Variable-Speed Turbines 1.3.3 Stall and Pitch Aerodynamic Power Controls 1.4 Wind Energy Conversion System Configurations 1.4.1 Fixed-Speed WECS without Power Converter Interface 1.4.2 Variable-Speed Systems with Reduced-Capacity Converters 1.4.3 Variable-Speed Systems with Full-Capacity Power Converters 1.5 Grid Code 1.5.1 Fault Ride-Through Requirements 1.5.2 Reactive Power Control 1.6 Summary References

1 1 2 2 3 3 4 8 9 10 12 12 13 14 14 17 20 20 21 22 22

2. Fundamentals of Wind Energy Conversion System Control 2.1 Introduction 2.2 Wind Turbine Components

25 25 26 v

CONTENTS

VI

2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 2.3 Wind 2.3.1 2.3.2

Turbine Blade Pitch Mechanism Gearbox Rotor Mechanical Brake Generator Yaw Drive Tower and Foundation Wind Sensors (Anemometers) Turbine Aerodynamics Power Characteristic of Wind Turbines Aerodynamic Power Control: Passive Stall, Active Stall, and Pitch Control 2.3.3 Tip Speed Ratio 2.4 Maximum Power Point Tracking (MPPT) Control 2.4.1 MPPT with Turbine Power Profile 2.4.2 MPPT with Optimal Tip Speed Ratio 2.4.3 MPPT with Optimal Torque Control 2.5 Summary References

27 29 30 32 33 33 35 36 37 38 39 42 43 45 46 46 47 47

3. Wind Generators and Modeling 3.1 Introduction 3.2 Reference Frame Transformation 3.2.1 abcldq Reference Frame Transformation 3.2.2 abclaß Reference Frame Transformation 3.3 Induction Generator Models 3.3.1 Construction 3.3.2 Space-Vector Model 3.3.3 dq Reference Frame Model 3.3.4 Simulation Model 3.3.5 Induction Generator Transient Characteristics 3.3.6 Steady-State Equivalent Circuit 3.4 Synchronous Generators 3.4.1 Construction 3.4.2 Dynamic Model of SG 3.4.3 Steady-State Equivalent Circuits 3.5 Summary References

49 49 50 51 53 55 55 56 58 59 61 65 71 72 75 80 85 85

4. Power Converters in Wind Energy Conversion Systems 4.1 Introduction 4.2 AC Voltage Controllers (Soft Starters) 4.2.1 Single-Phase AC Voltage Controller 4.2.2 Three-Phase AC Voltage Controller

87 87 88 89 92

CONTENTS

4.3 Interleaved Boost Converters 4.3.1 Single-Channel Boost Converter 4.3.2 Two-Channel Interleaved Boost Converter 4.3.3 Multichannel Interleaved Boost Converters 4.4 Two-Level Voltage-Source Converters 4.4.1 Sinusoidal PWM 4.4.2 Space Vector Modulation 4.4.3 Harmonic Analysis 4.5 Three-Level Neutral Point Clamped Converters 4.5.1 Converter Configuration 4.5.2 Space Vector Modulation 4.6 PWM Current Source Converters 4.6.1 Current Source Inverter Topology 4.6.2 Selective Harmonic Elimination 4.6.3 Space Vector Modulation 4.6.4 PWM Current Source Rectifier 4.7 Control of Grid-Connected Inverter 4.7.1 Voltage Oriented Control (VOC) 4.7.2 VOC with Decoupled Controller 4.7.3 Operation of Grid-Connected Inverter with VOC and Reactive Power Control 4.8 Summary References 5. Wind Energy System Configurations 5.1 Introduction 5.2 Fixed-Speed WECS 5.2.1 Single-Speed WECS 5.2.2 Two-Speed WECS 5.3 Variable-Speed Induction Generator WECS 5.3.1 Wound Rotor Induction Generator with External Rotor Resistance 5.3.2 Doubly Fed Induction Generator WECS with ReducedCapacity Power Converter 5.3.3 SCIG Wind Energy System with Full-Capacity Power Converters 5.4 Variable-Speed Synchronous Generator WECS 5.4.1 Configuration with Full-Capacity Back-to-Back Power Converters 5.4.2 Configuration with Diode Rectifier and dc/dc Converters 5.4.3 Configuration with Distributed Converters for Multiwinding Generators 5.5 Summary References

Vil

97 99 103 107 112 112 116 124 125 126 128 131 132 132 133 140 142 144 146 148 152 152 153 153 154 154 155 157 157 158 160 162 163 164 167 169 170

VIII

CONTENTS

6. Fixed-Speed Induction Generator WECS 6.1 Introduction 6.2 Configuration of Fixed-Speed Wind Energy Systems 6.2.1 Wind Turbine 6.2.2 Gearbox 6.2.3 Generator 6.2.4 Soft Starter 6.2.5 Reactive Power Compensation 6.2.6 Main Features and Drawbacks 6.3 Operation Principle 6.3.1 Fixed-Speed Operation of SCIG 6.3.2 Two-Speed Operation of Fixed-Speed WECS 6.4 Grid Connection with Soft Starter 6.5 Reactive Power Compensation 6.6 Summary References

173 173 174 174 175 175 176 176 177 177 177 179 180 184 188 189

7. Variable-Speed Wind Energy Systems with Squirrel Cage Induction Generators 7.1 Introduction 7.2 Direct Field Oriented Control 7.2.1 Field Orientation 7.2.2 Direct FOC for SCIG Wind Energy Systems 7.2.3 Rotor Flux Calculator 7.2.4 Dynamic and Steady-State Analysis of Direct FOC WECS 7.3 Indirect Field Oriented Control 7.3.1 Principles of Operation of Indirect FOC 7.3.2 Steady-State Analysis of Indirect FOC SCIG Wind Energy System 7.4 Direct Torque Control 7.4.1 Principle of Direct Torque Control 7.4.2 Switching Logic 7.4.3 Stator Flux and Torque Calculator 7.4.4 Transient Analysis of SCIG WECS with DTC 7.4.5 Steady-State Analysis of SCIG WECS with DTC 7.5 Control of Current Source Converter Interfaced WECS 7.5.1 Introduction 7.5.2 Control ofCSC WECS with Variable a and Fixed m 7.5.3 Steady-State Analysis of CSC WECS 7.6 Summary References

191

8. Doubly Fed Induction Generator Based WECS 8.1 Introduction 8.2 Super-and Subsynchronous Operation of DFIG

237 237 238

191 192 192 193 195 197 204 204 206 210 210 211 214 215 217 223 223 225 228 235 235

CONTENTS

8.3 Unity Power Factor Operation of DFIG 8.3.1 Steady-State Equivalent Circuit of DFIG with Rotor-Side Converter 8.3.2 Torque-Slip Characteristics of DFIG WECS 8.3.3 Steady-State Analysis of DFIG WECS with PFS = 1 8.3.4 Simplified Calculations 8.4 Leading and Lagging Power Factor Operation 8.5 Stator Voltage Oriented Control of DFIG WECS 8.5.1 Principle of Stator Voltage Oriented Control (SVOC) 8.5.2 System Block Diagram 8.5.3 Dynamic Performance of DFIG WECS 8.5.4 Steady-State Performance of DFIG WECS 8.6 DFIG WECS Start-Up and Experiments 8.7 Summary References

IX

240 240 246 249 251 252 254 254 259 261 265 269 272 273

9. Variable-Speed Wind Energy Systems with Synchronous Generators 9.1 Introduction 9.2 System Configuration 9.3 Control of Synchronous Generators 9.3.1 Zero ¿-Axis Current (ZDC) Control 9.3.2 Maximum Torque Per Ampere (MTPA) Control 9.3.3 Unity Power Factor (UPF) Control 9.3.4 Comparison ofZDC, MTPA and UPF Controls 9.4 SG Wind Energy System with Back-to-Back VSC 9.4.1 Nonsalient SG WECS with ZDC and Optimal Torque Control 9.4.2 Transient and Steady-State Analysis of Nonsalient SG WECS 9.4.3 Salient-Pole SG WECS with MTPA and Rotor Speed Feedback Controls 9.4.4 Transient and Steady-State Analysis of Salient-Pole SG WECS 9.4.5 Grid-Side MPPT Control Scheme 9.5 DC/DC Boost Converter Interfaced SG Wind Energy System 9.6 Reactive Power Control of SG WECS 9.7 Current Source Converter Based SG Wind Energy Systems 9.7.1 CSC Wind Energy Systems with Firing Angle Control 9.7.2 CSC Wind Energy System with Reactive Power Control 9.8 Summary References

275

Appendix A. Per-Unit System

317

Appendix B. Generator Parameters B. 1 Squirrel Cage Induction Generators

319 319

275 276 277 277 279 281 282 289 289 291 294 296 301 302 304 308 308 312 315 315

X

CONTENTS

B.2 Doubly Fed Induction Generators B.3 Synchronous Generators

322 324

Appendix C. Problems and Solutions

327

Index

449

IEEE Press Series on Power Engineering

PREFACE

Wind energy is clean and sustainable. It is one of the fastest growing renewable energy resources. The conversion of wind kinetic energy into electric energy is of a multidisciplinary nature, involving aerodynamics, mechanical systems, electric machines, power electronics, control theory, and power systems. In the past, a number of books have addressed some of these subjects. This book explores the power conversion and control of wind energy conversion systems (WECS) from the electrical engineering perspective. It provides a comprehensive and in-depth analysis of wind generators, system configurations, power converters, control schemes, and dynamic/steady-state performance of various practical wind energy systems. The book contains nine chapters. Chapter 1 provides a market survey and an overview of wind turbine technology, wind energy system classifications, costs, and grid codes for wind power integration. Chapter 2 introduces the fundamentals and control principles of wind energy systems, including wind turbine components, aerodynamics, stall and pitch controls, and maximum power point tracking schemes. Chapter 3 presents commonly used wind generators, including squirrel cage induction generators, doubly fed induction generators, and synchronous generators. The dynamic and steady-state models of these generators are also derived to facilitate the analysis of wind energy systems in the subsequent chapters. Chapter 4 discusses various power converters and PWM schemes used in wind energy systems. Both voltage and current source converters are presented with an emphasis on high-power wind energy system. Chapter 5 presents a general overview of configurations and characteristics of major practical WECS. Chapter 6 focuses on fixed-speed, inductor generator based wind energy systems; important issues such as grid connection, two-speed operation, and reactive power compensation are discussed. Chapter 7 deals with wind energy systems with variable-speed, squirrel cage induction generators (SCIG), in which typical system configurations and advanced control schemes such as field oriented controls (FOC) and direct torque control (DTC) are elaborated. Chapter 8 discusses doubly fed induction generator (DFIG) systems, where the subsynchronous and supersynchronous modes of operation are investigated. Chapter 9 is dedicated to variable-speed, synchronous generator wind systems, in which various control schemes, including zero d-axis current (ZDC) control, maximum xi

XII

PREFACE

torque per ampere (MTPA) control, and unity power factor (UPF) control, are analyzed in detail. To help the reader understand the principle and operation of various wind energy conversion systems, we have developed more than 30 case studies in the body of the book and more than 100 solved problems in Appendix C—Problems and Solutions. Therefore, this book is not only for academic researchers and practicing engineers as a reference book, but also suitable for graduate students and final-year undergraduate students as a textbook. We would like to express our sincere appreciation to Mr. Venkata Yaramasu, our Ph.D. student in the Laboratory for Electric Drive Applications and Research (LEDAR) at Ryerson University, for his great assistance in preparing the appendices and the first three sections of Chapter 4. We would like to thank our postdoctoral fellows and graduate students in LEDAR, in particular, Dr. Victor F. Liu, Dr. Moya J. Dai, Mr. Ning Zhu, and Mr. Ehsan Al-Nabi, for their kind assistance in preparing the manuscript. Our special thanks go to Wiley/IEEE Press editors for their great help and support. We also wish to acknowledge the support and inspiration of our families during the preparation of this book. BINWU YONGQIANG LANG NAVID ZARGARI SAMIR KOURO

Toronto, Ontario, Canada January 2011

LIST OF SYMBOLS

A sweep area of turbine rotor blades C, filter capacitor of current source inverter Cp power coefficient of blade Cp.max maximum power coefficient of blade filter capacitor of current source rectifier Cr D duty cycle of boost converter Z>! coefficient (Z), = L s L r - L„) in the m o d e l o f induction generators E DC capacitor voltage of three-level NPC converter battery voltage in DC link circuit / fundamental frequency of inverter output voltage fcr frequency of carrier wave in sinusoidal pulse width modulation fg frequency of the grid fm frequency of modulating wave in sinusoidal pulse width modulation f„ cut-off frequency of a first-order low-pass filter fs stator frequency of induction or synchronous generators fsp sampling frequency in space vector modulation fsw switching frequency of solid-state switching device fsw.inv equivalent switching frequency of inverter phase-a current of AC voltage controller phase-a current of the grid phase-a rotor current of induction generator phase a stator current of induction or synchronous generator phase-a PWM current of current source inverter phase-a PWM current of current source rectifier '■awr phase-6 current of AC voltage controller phase-6 current of the grid ibr phase-è rotor current of induction generator ibs phase-c stator current of induction or synchronous generator ibwi phase-Z) current of current source inverter phase-c current of AC voltage controller icid d-axis filter capacitor current in current source inverter