Doubly Fed Induction Machine E-Book

Gonzalo Abad

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: IEEE Press Series on Power Engineering
• Sprache: Englisch

Seitenzahl: 773

Veröffentlichungsjahr: 2011

Beschreibung

This book will be focused on the modeling and control of the DFIM based wind turbines. In the first part of the book, the mathematical description of different basic dynamic models of the DFIM will be carried out. It will be accompanied by a detailed steady-state analysis of the machine. After that, a more sophisticated model of the machine that considers grid disturbances, such as voltage dips and unbalances will be also studied. The second part of the book surveys the most relevant control strategies used for the DFIM when it operates at the wind energy generation application. The control techniques studied, range from standard solutions used by wind turbine manufacturers, to the last developments oriented to improve the behavior of high power wind turbines, as well as control and hardware based solutions to address different faulty scenarios of the grid. In addition, the standalone DFIM generation system will be also analyzed.

Leseprobe

Contents

Cover

Series Page

Title Page

Copyright

Preface

Chapter 1: Introduction to A Wind Energy Generation System

1.1 Introduction

1.2 Basic concepts of a Fixed Speed Wind Turbine (FSWT)

1.3 Variable Speed Wind Turbines (VSWTs)

1.4 Wind Energy Generation System Based on DFIM VSWT

1.5 Grid Code Requirements

1.6 Voltage Dips and LVRT

1.7 VSWT Based on DFIM Manufacturers

1.8 Introduction to the Next Chapters

Bibliography

Chapter 2: Back-to-Back Power Electronic Converter

2.1 Introduction

2.2 Back-to-Back Converter based on Two-Level VSC Topology

2.3 Multilevel VSC Topologies

2.4 Control of Grid Side System

2.5 Summary

References

Chapter 3: Steady State of the Doubly Fed Induction Machine

3.1 Introduction

3.2 Equivalent Electric Circuit at Steady State

3.3 Operation Modes Attending to Speed and Power Flows

3.4 Per Unit Transformation

3.5 Steady State Curves: Performance Evaluation

3.6 Design Requirements for the DFIM in Wind Energy Generation Applications

3.7 Summary

References

Chapter 4: Dynamic Modeling of the Doubly Fed Induction Machine

4.1 Introduction

4.2 Dynamic Modeling of the DFIM

4.3 Summary

References

Chapter 5: Testing the DFIM

5.1 Introduction

5.2 Off-line Estimation of DFIM Model Parameters

5.3 Summary

References

Chapter 6: Analysis of the DFIM Under Voltage Dips

6.1 Introduction

6.2 Electromagnetic Force Induced in the Rotor

6.3 Normal Operation

6.4 Three-Phase Voltage Dips

6.5 Asymmetrical Voltage Dips

6.6 Influence of the Rotor Currents

6.7 DFIM Equivalent Model During Voltage Dips

6.8 Summary

References

Chapter 7: Vector Control Strategies for Grid-Connected DFIM Wind Turbines

7.1 Introduction

7.2 Vector Control

7.3 Small Signal Stability of the Vector Control

7.4 Vector Control Behavior Under Unbalanced Conditions

7.5 Vector Control Behavior Under Voltage Dips

7.6 Control Solutions for Grid Disturbances

7.7 Summary

References

Chapter 8: Direct Control of the Doubly Fed Induction Machine

8.1 Introduction

8.2 Direct Torque Control (DTC) of the Doubly Fed Induction Machine

8.3 Direct Power Control (DPC) of the Doubly Fed Induction Machine

8.4 Predictive Direct Torque Control (P-DTC) of the Doubly Fed Induction Machine at Constant Switching Frequency

8.5 Predictive Direct Power Control (P-DPC) of the Doubly Fed Induction Machine at Constant Switching Frequency

8.6 Multilevel Converter based Predictive Direct Power and Direct Torque Control of the Doubly Fed Induction Machine at Constant Switching Frequency

8.7 Control Solutions for Grid Voltage Disturbances, Based on Direct Control Techniques

8.8 Summary

References

Chapter 9: Hardware Solutions for LVRT

9.1 Introduction

9.2 Grid Codes Related to LVRT

9.3 Crowbar

9.4 Braking Chopper

9.5 Other Protection Techniques

9.6 Summary

References

Chapter 10: Complementary Control Issues: Estimator Structures and Start-Up of Grid-Connected DFIM

10.1 Introduction

10.2 Estimator and Observer Structures

10.3 Start-up of the Doubly Fed Induction Machine Based Wind Turbine

10.4 Summary

References

Chapter 11: Stand-Alone DFIM Based Generation Systems

11.1 Introduction

11.2 Mathematical Description of the Stand-Alone DFIM System

11.3 Stator Voltage Control

11.4 Synchronization Before Grid Connection By Superior PLL

11.5 Summary

References

Chapter 12: New Trends on Wind Energy Generation

12.1 Introduction

12.2 Future Challenges for Wind Energy Generation: What must be Innovated

12.3 Technological trends: How they can be Achieved

12.4 Summary

References

Appendix

A.1 Space Vector Representation

A.2 Dynamic Modeling of the DFIM Considering the Iron Losses

References

Index

IEEE Press445 Hoes LanePiscataway, NJ 08854

IEEE Press Editorial Board Lajos Hanzo, Editor in Chief

R. AbariT. ChenO. MalikJ. AndersonT. G. CrodaS. NahavandiS. BasuS. FarshchiM. S. NewmanA. ChatterjeeB. M. HammerliW. Reeve

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

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

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Library of Congress Cataloging-in-Publication Data:

Doubly fed induction machine: modeling and control for wind energy generation /

G. Abad... [et al.].

p. cm.

Includes bibliographical references.

ISBN 978-0-470-76865-5 (hardback)

1. Induction generators–Mathematical models. 2. Induction generators–Automatic control. 3. Wind turbines–Equipment and supplies. I. Abad, G. (Gonzalo), 1976-

TK2451.D68 2011

621.31′6–dc22

2011006741

ePDF ISBN: 978-1-118-10494-1

ePub ISBN: 978-1-118-10495-8

oBook ISBN: 978-1-118-10496-5

10 9 8 7 6 5 4 3 2 1

Preface

Over the last years, there has been a strong penetration of renewal energy resources into the power supply network. Wind energy generation has played and will continue to play a very important role in this area for the coming years.

Doubly fed induction machine (DFIM) based wind turbines have undoubtedly arisen as one of the leading technologies for wind turbine manufacturers, demonstrating that it is a cost effective, efficient, and reliable solution. This machine, a key element of the wind turbine, is also known in the literature as the wound rotor induction machine (WRIM). It presents many similarities with the widely used and popular squirrel cage induction machine (SCIM). However, despite the parallelism of both machines, the DFIM requires its own specific study for an adequate understanding.

Although there have been a significant number of excellent textbooks on the subject of induction machine modeling and control, books containing a significant portion of material related to the DFIM are less common. Therefore, today this book seems to be the unique and comprehensive reference, exclusively dedicated to the DFIM modeling and control and applied to wind energy generation.

This book provides the reader with basic and advanced knowledge about DFIM based wind turbines, including market overview and tendencies, discussing realistic and practical problems with numerical and graphical illustrative examples, as well as providing guidance to help understand the new concepts.

The technical level of the book increases progressively along the chapters, covering first basic background knowledge, and later addressing advanced study of the DFIM. The book can be adopted as a textbook by nonexpert readers, undergraduate or postgraduate students, to whom the first chapters will help lay the groundwork for further reading. In addition, a more experienced audience, such as researchers or professionals involved in covered topics, would also benefit from the reading of this book, allowing them to obtain a high level of understanding and expertise, of DFIM based wind turbines.

It must be mentioned that, by means of this book, the reader not only will be able to learn from wind turbine technology or from the DFIM itself, but also enhance his/her knowledge on AC drives in general, since many aspects of this book present universal character and may be applied to different AC machines that operate on different applications.

On the other hand, it is the belief of the authors that what makes this DFIM based wind turbine technology cost effective (i.e., its reduced size converter requirement due to the double supply nature of the machine), makes its study challenging for new readers. The combination and coordination of the converter supply and grid supply, compared to single supplied machines such as asynchronous or synchronous machines, lead us to a more enriching environment in terms of conceptual understanding.

In addition, the direct grid supply can be a disadvantage, when the machine must operate under a faulty or distorted grid voltage scenario; especially if its disconnection must be avoided, fulfilling the generation grid code requirements. This mainly occurs because the stator windings of the machine are directly affected by those perturbations. In order to move forward with these problematic but realistic and unavoidable situations, additional active hardware protections or increased size of supplying converter are commonly adopted, accompanied by special control adaptations. Because of this, the work focuses on voltage disturbance analysis for DFIM throughout the book.

It is clear that this work is not intended to be a defense of DFIM based wind turbines, as the best technological solution to the existing alternative ones. Instead, the objective of this book is to serve as a detailed and complete reference, of the well established wind turbine concept.

No matter what the future holds, DFIM based wind turbines have gained an undoubtedly distinguished place that will always be recognized in the history of wind energy generation.

Finally, we would like to first express our sincere gratitude to Professor M. P. Kazmierkowski, for encouraging us to write this book. We wish to also thank everyone who has contributed to the writing of this book. During the last ten years, there have been a significant number of students, researchers, industry, and university colleagues who have influenced us, simply with technical discussions, or with direct and more concise contributions. Thanks to your daily and continuous support, this project has become a reality.

To conclude, we would like also to acknowledge IEEE Press and John Wiley & Sons, for their patience and allowance of the edition of the book.

Gonzalo Abad Jesús López Miguel A. Rodríguez Luis Marroyo Grzegorz Iwanski

Chapter 1

Introduction to A Wind Energy Generation System

1.1 Introduction

The aim of this chapter is to provide the basic concepts to understand a wind energy generation system and the way it must be operated to be connected to the utility grid.

It covers general background on wind turbine knowledge, not only related to the electrical system, but also to the mechanical and aerodynamics characteristics of wind turbines.

In Section 1.2 the components and basic concepts of a fixed speed wind turbine (FSWT) are explained, as an introduction to a modern wind turbine concept; also, energy extraction from the wind and power–torque coefficients are also introduced.

In Section 1.3 a simple model for the aerodynamic, mechanical, and pitch systems is developed together with a control system for a variable speed wind turbine (VSWT). This section explains the different configurations for the gearbox, generator, and power electronics converter, used in a VSWT.

Section 1.4 describes the main components of a wind energy generation system (WEGS), starting with a VSWT based on a doubly fed induction motor (DFIM); then a wind farm electrical layout is described and finally the overall control strategy for the wind farm and the wind turbine.

In Section 1.5, the grid integration concepts are presented since the rising integration of wind power in the utility grid demands more constraining connection requirements.

Since the low voltage ride through (LVRT) is the most demanding in terms of control strategy, Section 1.6 deals with the LVRT operation description. The origin, classification, and description of voltage dips are given in order to understand specifications for the LVRT. The section finishes by describing a grid model suitable to validate the LVRT response of wind turbines.

Section 1.7 provides a survey of solutions given by different wind turbine manufacturers. And finally a 2.4 MW VSWT is numerically analyzed.

To conclude, the next chapters are overviewed in Section 1.8.

1.2 Basic concepts of a Fixed Speed Wind Turbine (FSWT)

1.2.1 Basic Wind Turbine Description

The basic components of a wind turbine are described by means of a fixed speed wind turbine, based on a squirrel cage (asynchronous machine) and stall–pitch power control. This technology, developed in the late 1970s by pioneers in Denmark, was widely used during the 1980s and 1990s, and was the base of wind energy expansion in countries like Spain, Denmark, and Germany during the 1990s.

The main manufacturers developing this technology have been Vestas, Bonus (Siemens), Neg-Micon and Nordtank, in Denmark, Nordex and Repower in Germany, Ecotècnia (Alstom), Izar-Bonus and Made in Spain, and Zond (Enron-GE) in the United States. At present, many other small manufacturers and new players such as Sulzon in India or GoldWind in China are in the market.

The first fixed speed wind turbines were designed and constructed under the concept of reusing many electrical and mechanical components existing in the market (electrical generators, gearboxes, transformers) looking for lower prices and robustness (as the pioneers did when they manufactured the first 25 kW turbines in their garages in Denmark). Those models were very simple and robust (most of them are still working, and there is a very active secondhand market).

To achieve the utility scale of 600,750, and 1000 kW, development of wind turbines took only ten years, and around two-thirds of the world's wind turbines installed in the 1980s and 1990s were fixed speed models.

Before we describe the FSWT, let's have a look at the main concepts related to this technology:

The fixed speed is related to the fact that an asynchronous machine coupled to a fixed frequency electrical network rotates at a quasifixed mechanical speed independent of the wind speed.The stall and pitch control will be explained later in the chapter, but is related to the way the wind turbine limits or controls the power extracted from the wind.

Figure 1.1 shows the main components of a fixed speed wind turbine.

Figure 1.1 Main components of a fixed speed wind turbine.

The nacelle contains the key components of the wind turbine, including the gearbox and the electrical generator. Service personnel may enter the nacelle from the tower of the turbine.

To the left of the nacelle we have the wind turbine rotor, that is, the rotor blades and the hub. The rotor blades capture the wind and transfer its power to the rotor hub. On a 600 kW wind turbine, each rotor blade measures about 20 meters in length and is designed much like the wing of an aeroplane.

The movable blade tips on the outer 2–3 meters of the blades function as air brakes, usually called tip brakes. The blade tip is fixed on a carbon fiber shaft, mounted on a bearing inside the main body of the blade. On the end of the shaft inside the main blade, a construction is fixed, which rotates the blade tip when subjected to an outward movement. The shaft also has a fixture for a steel wire, running the length of the blade from the shaft to the hub, enclosed inside a hollow tube.

During operation, the tip is held fast against the main blade by a hydraulic cylinder inside the hub, pulling with a force of about 1 ton on the steel wire running from the hub to the blade tip shaft.

When it becomes necessary to stop the wind turbine, the restraining power is cut off by the release of oil from the hydraulic cylinder, thereby permitting centrifugal force to pull the blade tip outwards. The mechanism on the tip shaft then rotates the blade tip through 90 degrees, into the braking position. The hydraulic oil outflow from the hydraulic cylinder escapes through a rather small hole, thus allowing the blade tip to turn slowly for a couple of seconds before it is fully in position. This thereby avoids excessive shock loads during braking.

The tip brakes effectively stop the driving force of the blades. They cannot, however, normally completely stop blade rotation, and therefore for every wind speed there is a corresponding freewheeling rotational speed. The freewheeling rotational speed is much lower than the normal operational rotational speed, so the wind turbine is in a secure condition, even if the mechanical brake should possibly fail.

The hub of the rotor is attached to the low speed shaft of the wind turbine. The low speed shaft of the wind turbine connects the rotor hub to the gearbox. On a 600 kW wind turbine, the rotor rotates relatively slowly, about 19–30 revolutions per minute (rpm).