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ADDIS ABABA UNIVERSITY
ADDIS ABABA INSTITUTE OF TECHNOLOGY (AAiT)
SCHOOL OF ELECTRICAL & COMPUTER ENGINEERING
DEPARTMENT OF ELECTRICAL ENGINEERING

STUDY OF DOUBLY FED INDUCTION GENERATOR CONTROL UNDER
GRID FAULT CONDITIONS

A thesis submitted to Addis Ababa Institute of Technology, School of
Graduate Studies, Addis Ababa University
in partial fulfillment of the requirement for the Degree of Master of Science in
Control Engineering

By
Teshale Tadesse
Advisor: Dr. Mengesha Mamo
ADDIS ABABA, ETHIOPIA
June, 2016
ADDIS ABABA UNIVERSITY
ADDIS ABABA INSTITUTE OF TECHNOLOGY (AAiT)
SCHOOL OF ELECTRICAL & COMPUTER ENGINEERING
DEPARTMENT OF ELECTRICAL ENGINEERING

STUDY OF DOUBLY FED INDUCTION GENERATOR CONTROL UNDER
GRID FAULT CONDITIONS

By:-TESHALE TADESSE
APPROVED BY BOARD OF EXAMINERS
_______________________ __________________
Chairman, Department of Graduate Committee Signature
Dr. Mengesha Mamo __________________
Advisor Signature
Dr. Getachewu Biru __________________
Internal Examiner Signature
Prof. N.P. Singh __________________
External Examiner Signature
Study of Doubly Fed Induction Generator Control under Grid Fault 2016

Conditions

Declaration

I, the undersigned, declare that this thesis work is my original work, has not been presented for a degree in
this or any other universities, and all sources of materials used for the thesis work have been fully
acknowledged.
Teshale Tadesse _____________________
Name Signature

Place: Addis Ababa Institute of Technology, Addis Ababa University, Addis Ababa

Date of Submission: May, 2016

This thesis has been submitted for examination with my approval as a university advisor.
Dr. Mengesha Mamo _____________________
Advisor‘s Name Signature
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Study of Doubly Fed Induction Generator Control under Grid Fault 2016

Conditions

Acknowledgement
Primarily, I would like to give glory to God and the Virgin Mary without which the completion of this thesis
would have been unthinkable. Next, I would like to express my deepest gratitude to my advisor, Dr.
Mengesha Mamo for his expertise guidance, constructive comments, suggestions and encouragement. He
has been a constant source of inspiration throughout this work. I am also grateful to thank Mr. Andinet
Negash for his kind help , advices and materials support. Last but not least, I would like to thank my family,
classmate Amdail Shefaw, friends who stood always by my side.

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CONTROL ENGINEERING | Acknowledgement
Study of Doubly Fed Induction Generator Control under Grid Fault 2016

Conditions

Abstract
Wind power is growing rapidly around the world as a means of dealing with the world energy shortage and
associated environmental problems. A wind electrical generation system is the most cost effective of all the
environmentally clean and safe renewable energy sources in world.
In this thesis, double fed induction generator and grid system are modeled under normal conditions of the
grid system and under grid faulty conditions. Any abnormalities associates with grid are going to affect the
system performance. Taking this into account, the performance of double fed induction generator (DFIG)
variable speed wind turbine under network faults is studied using simulation developed in
MATLAB/SIMULINK results show the fault behavior of the double fed induction generator when a sudden
short circuit and voltage dip on the grid side. After the clearance the short circuit fault and voltage dip the
proportional integral controller manages to restore the wind turbine‘s normal operation.
The three-phase fault model is done by giving a fault equivalent resistance value of 0.01Ω and voltage dip at
grid side with the value of 0.45p.u. At this time, the current, voltage, active power and reactive power value
of DFIG is fluctuating between 0.2p.u and 1.36p.u, 0.7p.u and 1.12p.u, 0 and 6MW, 0.75 and 0.42MVAr,
respectively. But in order to operate at normal operation the DFIG current and voltage value is at 1p.u. The
maximum active power that generated from DFIG is 9MW. To stabilize the system the proportional integral
controller compare the reference voltage and current with generated and minimize the error between voltage
and current. The proportional integral controller minimizes the error by decreasing the rising time and
makes the value of current and voltage to 1p.u. The detailed results of steady state and faulty or three-phase
short circuit on grid system has been noted and analyzed with proper justification. In order to increase the
fault ride through capabilities of the system, crowbar protection and series dynamic resistor could be added
to the system.
This thesis done by modeling and simulating of the controller using Matlab/Simulink in wind turbine system
integrated with grid system. Finally, we observed and interpreted the result with Matlab/Simulink
simulation software.
Keywords:- , doubly fed induction generator; wind turbine; proportional integral controller;
MATLAB/SIMULINK;
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Study of Doubly Fed Induction Generator Control under Grid Fault 2016

Conditions

Contents
Acknowledgement .............................................................................................................................................................i
Abstract ..............................................................................................................................................................................i
Contents ........................................................................................................................................................................... iii
List of Figures .................................................................................................................................................................. vii
List of Tables ..................................................................................................................................................................... ix
List of Abbreviations ......................................................................................................................................................... x
1. Chapter One: Introduction ....................................................................................................................................... 1
1.1. Background ...................................................................................................................................................... 1
1.2. Statement of the Problem ............................................................................................................................... 5
1.3. Objective of Thesis ........................................................................................................................................... 6
1.3.1. General Objective ..................................................................................................................................... 6
1.3.2. Specific Objectives ................................................................................................................................... 6
1.4. Literature Review ............................................................................................................................................. 6
1.5. Motivation for this Thesis ................................................................................................................................ 8
1.6. Contribution of the Thesis................................................................................................................................ 8
1.7. Thesis Outline ................................................................................................................................................... 9
2. Chapter Two: Induction Machines ......................................................................................................................... 10
2.1. Introductions .................................................................................................................................................. 10
2.2. Dynamic d-q Model ........................................................................................................................................ 11
2.2.1. Axes Transformation .............................................................................................................................. 12
2.2.2. Synchronously Rotating Reference Frame-Dynamic Model (Kron's equation) ..................................... 14
2.2.3. The Equivalent Circuit of a DFIG ............................................................................................................. 14
2.2.4. The Equivalent Circuit of a DFIG under Fault Conditions ....................................................................... 16
2.3. Wind Turbine and Wind Energy Conversion System ..................................................................................... 19
2.3.1. Wind Turbine .......................................................................................................................................... 19
2.3.2. Annual Wind Distribution ....................................................................................................................... 22
2.3.3. Power Extracted from the Wind ............................................................................................................ 23
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Conditions

2.4. Doubly Fed Induction Generator ................................................................................................................... 28
2.4.1. Fixed Speed Wind Turbine Generators .................................................................................................. 28
2.4.2. Variable Speed Wind Turbine Generators ............................................................................................. 28
2.4.3. The Advantage of a DFIG Configuration ................................................................................................. 29
2.5. Classification of Wind Turbine based on Generation Technologies .............................................................. 30
2.5.1. Type 1: Fixed-Speed Wind Turbines ....................................................................................................... 31
2.5.2. Type 2: Variable-Slip Wind Turbines ...................................................................................................... 31
2.5.3. Type 3: Doubly-Fed Induction Generator (DFIG) Wind Turbines ........................................................... 32
2.5.4. Type 4: Full-Converter Wind Turbines ................................................................................................... 33
2.6. Operating Principle of DFIG............................................................................................................................ 34
2.6.1. DFIG Capability Curves and the Coordinated Reactive Power Controller.............................................. 35
2.6.1.1. Two- Mass Model ............................................................................................................................... 35
2.6.1.2. DFIG Reactive Power Capability Characteristics ................................................................................ 35
2.7. Double Fed Induction Generator under Fault ................................................................................................ 37
2.7.1. Introduction ........................................................................................................................................... 37
2.7.2. DFIG Wind Turbine under Grid Fault Condition ..................................................................................... 37
2.7.3. DFIG Wind Turbine Behavior Immediately after the Fault .................................................................... 38
2.7.4. DFIG Wind Turbine Behavior at Fault Clearance Time ........................................................................... 38
2.8. DFIG Protection Schemes during Grid Faults ................................................................................................. 39
2.8.1. Crowbar Protection ................................................................................................................................ 39
2.8.2. DC-Chopper ............................................................................................................................................ 39
2.8.3. Series Dynamic Resistor ......................................................................................................................... 39
3. Chapter Three: Power Flow Control in Wind Turbine ............................................................................................ 41
3.1. Overall Power Flow in DFIG Wind Turbine System during Grid Fault ............................................................ 41
3.1.1. Mechanical Linkage ................................................................................................................................ 42
3.1.1.1. Aerodynamic Input ............................................................................................................................. 42
3.1.1.2. Mechanical Output ............................................................................................................................. 42
3.1.1.3. Inherent Short-Term Storage and Damping....................................................................................... 43
3.1.1.4. Aerodynamic and Mechanical Control ............................................................................................... 43
3.1.2. Electrical Linkage .................................................................................................................................... 43
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Conditions

3.1.2.1. Grid Side Transmission Lines .............................................................................................................. 43
3.1.2.2. Point of Interconnection to Substation .............................................................................................. 44
3.1.2.3. Generators and Power Converters .................................................................................................... 44
3.1.2.4. Power Converters ............................................................................................................................... 44
3.2. Power Balance Relations ................................................................................................................................ 44
3.2.1. Active Power Balance ............................................................................................................................. 44
3.2.2. Reactive Power Balance ......................................................................................................................... 47
3.3. Modes of Operation of DFIG .......................................................................................................................... 48
3.3.1. Characteristics of the DFIG Wind Turbine System ................................................................................. 48
3.3.1.1. Sub-synchronous Motoring ................................................................................................................ 49
3.3.1.2. Super-synchronous Motoring ............................................................................................................ 50
3.3.1.3. Super-synchronous Generating ......................................................................................................... 50
3.3.1.4. Sub-synchronous Generating ............................................................................................................. 51
4. Chapter Four: Controller Design ............................................................................................................................ 52
4.1. Introduction .................................................................................................................................................... 52
4.2. Parameter Selection of the Actuator .............................................................................................................. 52
4.3. Proportional-Integral Controller ..................................................................................................................... 54
4.4. Design of Inner Control Loop ........................................................................................................................ 58
4.5. Design of Outer Control Loop ....................................................................................................................... 61
5. Chapter Five: Simulation and Result Discussion .................................................................................................... 64
5.1. Introduction ................................................................................................................................................... 64
5.2. Simulation Model Description ....................................................................................................................... 64
5.2.1. Detail Description of Simulink Model ........................................................................................................ 64
5.2.2. Physical System of the DFIG Wind Turbine Connected to the Grid System .............................................. 65
5.2.3. Wound Rotor Induction Machine Parameters ........................................................................................... 65
5.3. Operational Characteristics of a DFIG at Normal Condition of the Grid System ........................................... 66
5.3.1. Converter Control System .......................................................................................................................... 66
5.3.1.1. Rotor Side Converter Control System .................................................................................................... 66
5.3.1.2. Grid Side Converter Control System ...................................................................................................... 70
5.3.1.3. Pitch Angle Control System .................................................................................................................... 72
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Conditions

5.4. Simulation Block Diagram and Results ........................................................................................................... 73
5.4.1. Simulation Result of DFIG under without Grid Fault Conditions ............................................................... 74
5.4.2. Simulation Result of DFIG under Grid Fault Conditions with PI controller ................................................ 79
5.4.2.1. Simulation of a voltage sag/dip on the 15kV system and short-circuit on grid side.......................... 80
5.4.2.1.1. Simulation Result Discussion for Wind Turbine Side ......................................................................... 81
5.4.2.1.2. Simulation Result Discussion for Grid Side Parameters ..................................................................... 83
5.4.3. DFIG Wind Turbine System Disconnected from Grid System .................................................................... 85
5.4.4. Simulation of a voltage sag/dip on the 15kV system and short-circuit on grid side without controller ... 90
6. Chapter Six: Conclusions, Recommendations and Future Works .......................................................................... 93
6.1. Conclusions .................................................................................................................................................... 93
6.2. Recommendation ........................................................................................................................................... 93
6.3. Future Works .................................................................................................................................................. 93
REFERENCES ................................................................................................................................................................... 95
APPENDIX ....................................................................................................................................................................... 98
Appendix A:1.5MW DFIG Parameters ........................................................................................................................ 98
Appendix B: Doubly fed induction generator modeling ............................................................................................. 99
Appendix C: Transfer Functions the Modified Inner Loop Control Structure .......................................................... 101
Appendix D: The Outer Loop Transfer Function ...................................................................................................... 102
Appendix E: Initialization Script ............................................................................................................................... 103

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Conditions

List of Figures
Figure 1.1 DFIG wind turbine integrated with grid system ............................................................................................. 4
Figure 2.1 Stationary frame a-b-c to d-q axes transformation ....................................................................................... 13
Figure 2.2 Stationary frame d-q to synchronous rotating frame d-q .............................................................................. 13
Figure 2.3 The equivalent circuit of d-axis .................................................................................................................... 15
Figure 2.4 The equivalent circuit of q-axis .................................................................................................................... 15
Figure 2.5 The equivalent circuits of q-axis under fault conditions ............................................................................... 16
Figure 2.6 The equivalent circuits of d-axis under fault conditions ............................................................................... 17
Figure 2.7 Block diagram of wind energy conversion system ....................................................................................... 20
Figure 2.8 Weibull distributions for wind speeds: 5.4m/s, 6.8m/s and 8.2m/s .............................................................. 23
Figure 2.9 A 1.5MW wind turbine curves ..................................................................................................................... 27
Figure 2.10 General wind turbine characteristics curve ................................................................................................ 29
Figure 2.11 Fixed-speed wind turbine schematics ......................................................................................................... 31
Figure 2.12 Variable-slip wind turbine schematics ........................................................................................................ 32
Figure 2.13 DFIG wind turbine schematics ................................................................................................................... 33
Figure 2.14 Full-converter wind turbine schematics ...................................................................................................... 33
Figure 2.15 DFIG capability curve; a) RSC and b) GSC ............................................................................................... 36
Figure 2.16 DFIG rotor equivalent circuits with all protection schemes ....................................................................... 40
Figure 3.1 DFIG power flow control ............................................................................................................................. 41
Figure 3.3 Overall energy flows in grid systems ........................................................................................................... 42
Figure 3.4 Natural curve of slip for the DFIG (full load torque and current) ................................................................ 49
Figure 3.5 Power flow in sub-synchronous motoring mode .......................................................................................... 50
Figure 3.6 Power flow in the super-synchronous motoring mode ................................................................................. 50
Figure 3.7 Power flow in the super-synchronous generating mode ............................................................................... 51
Figure 3.8 Power flow in sub-synchronous generating mode ........................................................................................ 51
Figure 4.1 Proportional control of a first-order plant ..................................................................................................... 52
Figure 4.2 PI controller system ...................................................................................................................................... 56
Figure 4.3 Standard cascading control structure ............................................................................................................ 58
Figure 4.4 Top: the d-axis control loop regulating Q, Bottom: the q-axis control loop regulating P .......................... 58
s s
Figure 4.5 Top: standard PI configuration, Bottom: Tapia's modified configuration .................................................... 59
Figure 4.6 Outer control loops-Top: reactive power loop; Bottom: real power loop..................................................... 63
Figure 5.1 Overview of the simulation .......................................................................................................................... 65
Figure 5.2 Wind turbine power characteristics curve .................................................................................................... 68
Figure 5.3 Matlab/Simulink of voltage control system in rotor side of DFIG ............................................................... 69
Figure 5.4 Matlab/Simulink of power control system in rotor side of DFIG ................................................................. 69
Figure 5.5 Matlab/Simulink of current control system in rotor side of DFIG ............................................................... 70
Figure 5.6 GSC control system ...................................................................................................................................... 71
Figure 5.7 Grid side current control system Matlab/Simulink diagram ......................................................................... 71
Figure 5.8 Phasor simulation of wind farm using DFIG wind turbines ......................................................................... 73
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