Wind electrical power systems are recently getting lot of attention, because
they are cost competitive, environmental clean and safe renewable power
source, as compared with fossil fuel and nuclear power generation. A special
type of induction generator, called a doubly fed induction generator (DFIG),
is used extensively for high-power wind applications. They are used more
and more in wind turbine applications due to ease controllability, high
energy efficiency and improved power quality.
This thesis aims to develop a method of a field orientation scheme for
control both the active and reactive powers of a DFIG driven by a wind
turbine.The proposed control system consists of a wind turbine that drives a
DFIG connected to the utility grid through AC-DC-AC link. The main
control objective is to regulate the dc link voltage for operation at maximum
available wind power.This is achieved by controlling the and axes
components of voltages and currents for both rotor side and line side
converters using PI controllers. The complete dynamic model of the
proposed system is described in detail. Computer simulations have been
carried out in order to validate the effectiveness of the proposed system
during the variation of wind speed. The results prove that , better overall
performances are achieved, quick recover from wind speed disturbances in
addition to good tracking ability.
Generally, any abnormalities associated with grid asymmetrical faults are
going to affect the system performance considerably. During grid faults,
unbalanced currents cause negative effects like overheating problems and
mechanical stress due to high torque pulsations that can damage the rotor shaft, gearbox or blade assembly. Therefore, the dynamic model of the
DFIG, driven by a wind turbine during grid faults has been analyzed and
developed using the method of symmetrical components. The dynamic
performance of the DFIG during unbalanced grid conditions is analyzed and
described in detail using digital simulations.
A novel fault ride-through (FRT) capability is proposed (i.e. the ability of
the power system to remain connected to the grid during faults) with suitable
control strategy in this thesis. In this scheme, the input mechanical energy of
the wind turbine during grid faults is stored and utilized at the moment of
fault clearance, instead of being dissipated in the resistors of the crowbar
circuit as in the existing FRT schemes. [...]
Table of Contents
CHAPTER (1) INTRODUCTION
1-1 General
1-2 Thesis Objectives
1-3 Thesis Outlines
CHAPTER (2) LITERATURE REVIEW
2-1 Introduction
2-2 Synchronous Generators Driven by a fixed speed Turbine
2-2-1 Wound Field Synchronous Generator (WFSG) Driven by a wind turbine
2-2-2 Permanent-Magnet Synchronous Generator (PMSG) Driven by a wind turbine
2-3 Induction Generators Driven by a variable speed wind turbine
2-3-1 Squirrel Cage Induction Generator (SCIG) Driven by a wind turbine
2-3-2 Doubly Fed Induction Generator (DFIG) Driven by a wind turbine
2-4 Field oriented Control
2-4-1 Direct field oriented control of a wind driven DFIG
2-4-2 Indirect field oriented control of a wind driven DFIG
2-5 Enhancement techniques of DFIG performance during grid faults
2-5-1 Traditional techniques for protection of wind turbines during grid faults
2-5-2 Crowbar protection technique
2-5-2-1 Series antiparallel thyristors LVRT technique
CHAPTER (3) Field Orientation Control of a Wind Driven DFIG Connected to the Grid
3-1 Introduction
3-2 System description
3-3 Dynamic modeling of the DFIG
3-3-1 Turbine model
3-3-2 Induction machine model
3-4 DC Link model
3-5 Complete system model
3-6 Field oriented control of DFIG
3-7 Complete system configuration
3-8 Simulation results and discussions
CHAPTER (4) Dynamic Performance of a Wind Driven Doubly Fed Induction Generator During Grid Faults
4-1 Introduction
4-2 Dynamic Model of a DFIG System
4-3 Mathematical Model of DFIG System Under Unbalanced Grid Voltage
4-4 System Description
4-5 Simulation results and discussions
CHAPTER (5) Enhancement of Fault Ride through Capability of a Wind Driven Doubly Fed Induction Generator Connected to the Grid
5-1 Introduction
5-2 System under study and proposed FRT scheme
5-3 Control strategy of the proposed FRT scheme
5-4 Choice of size of storage inductor
5-5 Simulation results and discussions
CHAPTER (6) Conclusions and Recommendations
6-1 Conclusions
6-2 Recommendations for future work
Objectives and Research Themes
The thesis focuses on the performance and control of a Doubly Fed Induction Generator (DFIG) driven by wind turbines, specifically addressing the challenges of maintaining system stability during unbalanced grid faults. The primary objective is to develop a field orientation control method for optimal power regulation and to introduce a novel fault ride-through (FRT) scheme that utilizes stored mechanical energy to enhance grid connectivity during fault conditions.
- Mathematical modeling of DFIG-based wind energy conversion systems.
- Implementation of field-oriented control for active and reactive power regulation.
- Dynamic analysis of DFIG performance under various grid fault conditions.
- Development of a cost-effective fault ride-through (FRT) scheme to prevent generator disconnection.
- Validation through extensive MATLAB/SIMULINK simulation studies.
Excerpt from the Book
2.5.1. Traditional Techniques for Protection of a Wind Driven DFIG During Grid Faults
In the past, the protection requirements of wind turbines were focused on safe-guarding the turbines themselves. When the network suffers any transient disturbance such as voltage sag or short circuit fault, the wind turbine generators are usually disconnected from the grid as soon as the occurrence of voltage dip in the range of 70–80%. However, with large integration of wind generators in the power system network, loss of considerable part of wind generators following a transient disturbance is not preferable. Tripping of numerous wind generators during transient disturbance can further risk the stability of power system thereby contributing to amplification of the effect of the disturbance that has originated.
According to recent grid code requirement [26], wind generators should remain connected and actively support the grid during network fault or any other transient disturbance. Therefore, it has become inevitable for existing and new upcoming wind generators to be equipped with ‘‘fault ride-through (FRT) or low voltage ride-through (LVRT) or zero voltage ride through (ZVRT) schemes’’ to avoid their disconnection from the power system network during grid faults. Moreover, FRT is extremely important for maintaining system reliability and voltage stability, especially in areas where concentration of wind power generation facilities are high.
Summary of Chapters
CHAPTER (1) INTRODUCTION: Provides an overview of wind energy, the motivations for using DFIG in wind farms, and outlines the core objectives of the thesis.
CHAPTER (2) LITERATURE REVIEW: Reviews existing wind generation technologies, various generator types, and current control methods, including traditional FRT protection techniques.
CHAPTER (3) Field Orientation Control of a Wind Driven DFIG Connected to the Grid: Presents the dynamic model of the DFIG system and details the field-oriented control scheme designed for active and reactive power management.
CHAPTER (4) Dynamic Performance of a Wind Driven Doubly Fed Induction Generator During Grid Faults: Analyzes the transient behavior of the DFIG system under various unbalanced grid conditions using the method of symmetrical components.
CHAPTER (5) Enhancement of Fault Ride through Capability of a Wind Driven Doubly Fed Induction Generator Connected to the Grid: Introduces a novel FRT scheme that stores mechanical energy to improve DFIG stability during grid faults and performs extensive simulation validations.
CHAPTER (6) Conclusions and Recommendations: Summarizes the key findings regarding the proposed FRT scheme's effectiveness and provides suggestions for future research using artificial intelligence.
Keywords
Wind energy, Doubly Fed Induction Generator, DFIG, Grid faults, Field oriented control, Fault ride-through, FRT, LVRT, Renewable energy, Power electronics, MATLAB, SIMULINK, Symmetrical components, Wind turbine, Power system stability.
Frequently Asked Questions
What is the core focus of this research?
The research focuses on controlling wind-driven Doubly Fed Induction Generators (DFIG) to improve performance and maintain grid connectivity during unstable grid conditions and faults.
What are the primary themes addressed in the work?
Key themes include the dynamic modeling of DFIGs, the implementation of field-oriented control (FOC) for power management, and the design of novel fault ride-through (FRT) strategies.
What is the main research objective?
The primary goal is to enhance the fault ride-through capability of DFIGs, allowing them to stay connected to the grid during faults instead of being disconnected.
Which scientific methodology is utilized?
The study utilizes mathematical modeling, the method of symmetrical components for analyzing grid faults, and extensive computer simulations performed in MATLAB/SIMULINK.
What topics are discussed in the main body?
The main body covers the theoretical background of DFIG systems, field orientation principles, modeling of system dynamics during faults, and the design and simulation of a new FRT scheme.
How is the work characterized by keywords?
The work is characterized by terms such as DFIG, Fault ride-through, Field oriented control, Grid integration, and Wind power system stability.
How does the proposed FRT scheme differ from traditional crowbar methods?
Unlike the crowbar method, which dissipates excess energy as heat, the proposed FRT scheme stores the input mechanical energy of the wind turbine during a fault and utilizes it after fault clearance.
What is the benefit of the proposed FRT scheme according to the simulation results?
The simulation results demonstrate that the proposed scheme effectively reduces transient oscillations, prevents generator disconnection, and provides rapid reestablishment of terminal voltage following a fault.
- Citar trabajo
- Mahmoud Mossa (Autor), 2013, Control of a Wind Driven Doubly Fed Induction Generator During Grid Faults, Múnich, GRIN Verlag, https://www.grin.com/document/209083
