Wind generation has become the most important alternate energy source and has experienced increased progress in India during the past decade. While it has great potential as an alternative to less environmentally friendly energy sources, there are various technical challenges that cause wind to be considered negatively by many utilities. Wind energy conversion systems suffer from the fact that their real power generation is closely dependent on the local environmental conditions.
The Doubly Fed Induction Generator (DFIG) based wind turbine with variable-speed variable-pitch control scheme is the most popular wind power generator in the wind power industry. This machine can be operated either in grid connected or standalone mode.
In this thesis, a detailed electromechanical model of a DFIG-based wind turbine connected to power grid as well as separately operated wind turbine system with different sub-systems is developed in the MATLAB/SIMULINK environment and its equivalent generator and turbine control structure is realized. In this regard following configurations have been considered:
• DFIG with Battery storage sub-system
• DFIG with Buck-Boost converter
• DFIG with transformer
• DFIG with 3-winding transformer
Addition of battery storage and buck-boost converter sub-systems into the system enables not only dispatching of generator power but also decreases the variability in their reactive power requirements. The full control over both active and reactive power is possible by the use of transformer between DFIG and rotor side converter.
The steady state behavior of the overall wind turbine system is presented and the steady state reactive power ability of the DFIG is analyzed. It has been shown that major part of the reactive power should be supplied from rotor side converter to reduce the overall rating of the generator.
The DFIG with above mentioned sub-systems is connected to grid. The total harmonic distortion analysis and efficiency are carried out. It is found that DFIG with transformer in between machine and rotor side converter has lowest THD (2.29%) and DFIG with 3-winding transformer has maximum efficiency (above 93%).
Table of Contents
CHAPTER 1: INTRODUCTION
1.1 GENERAL
1.2 BACKGROUND
1.3 WIND ENERGY
1.4 STATE OF ART
1.4.1 Classification of Wind Turbine
1.4.2 Types of Wind Generators
1.5 DOUBLY-FED INDUCTION GENERATOR
1.5.1 Advantages of DFIGs
1.6 POWER CONVERTERS
1.7 ENERGY STORAGE SYSTEMS
1.7.1 Advantages of ESS
1.7.2 Types of ESS
1.8 BUCK-BOOST CONVERTER
1.8.1 Main Advantage of Buck-Boost Converter
1.9 POWER SYSTEM INTERCONNECTION
1.9.1 Transformer
1.9.2 Advantages of Transformer in Rotor Circuit of DFIG
1.10 WIND POWER CHALLENGES
1.11 TECHNICAL CHALLENGES
1.12 PROBLEM FORMULATION AND METHODOLOGY
1.13 OUTLINE OF THESIS
CHAPTER 2: LITERATURE REVIEW
2.1 GENERAL
2.2 LITERATURE REVIEW
CHAPTER 3: MODDELING, OPERATION AND CONTROL OF DFIG
3.1 GENERAL
3.1.1 DFIG Based Wind Energy Conversion System
3.1.2 Steady-State Equivalent Circuit
3.2 REACTIVE POWER CONTROL
3.2.1 Reactive Power Sources
3.2.2 Optimum Reactive Power Distribution
3.3 TRANSIENT MODELS AND CONTROL OF DFIG
3.3.1 Power Converter Controls
3.3.1.1 Rotor Side Converter Control
3.3.1.2 Current Regulator Control
3.3.2. Grid Side Converter Control
3.3.2.1 The Simulink Model of Current Regulator Control and Dc Voltage Regulator
3.4 SPEED CONTROL
3.5 AC VOLTAGE REGULATION
3.6. DECOUPLED CONTROL OF ACTIVE AND REACTIVE POWERS
3.7 CONCLUSIONS
CHAPTER 4: INTERCONNECTION OF DFIG WITH DIFFERENT SUB-SYSTEMS
4.1 INTEGRATION OF ENERGY STORAGE SUB-SYSTEM
4.1.1 Energy Storage Sub-System
4.1.2 DFIG with Energy Storage Sub-System
4.1.3Simulink Based Model of DFIG with Battery Energy Storage Sub-System
4.1.4 Energy Storage Control
4.1.5 Grid Side Converter
4.1.6 Energy Storage System Characteristics
4.1.6.1 Operating Characteristics at Constant Wind Speed
4.1.6.2 Operating Characteristics at Variable Wind Speed
4.2 DFIG WITH BUCK/BOOST CONVERTOR
4.2.1 Series Compensation Concept
4.2.2 Buck and Boost Mode
4.2.3Simulink Based Model of DFIG with Buck-Boost Converter Sub- System
4.2.3.1 Buck-Boost Converter Control
4.2.4 Buck-Boost Converter Characteristics
4.2.4.1 Operating Characteristics at Constant Wind Speed
4.2.4.2 Operating Characteristics at Variable Wind Speeds
4.3 DFIG WITH TRANSFORMER IN ROTOR SIDE CIRCUIT
4.3.1 Simulink Based Model of DFIG with Transformer in Between Machine and Rotor Side Converter
4.3.2 Transformer Characteristics
4.3.2.1 Operating Characteristics at Constant Wind Speed
4.3.2.2 OPERATING CHARACTERISTICS AT VARIABLE WIND SPEEDS
4.4 DFIG WITH 3-WINDING TRANSFORMER
4.4.1 Simulink Model of DFIG with 3-winding Transformer
4.4.2 3-Winding Transformer Characteristics
4.4.2.1 Operating Characteristics at Constant Wind Speed
4.4.2.2 OPERATING CHARACTERISTICS AT VARIABLE WIND SPEEDS
4.4 CONCLUSIONS
CHAPTER 5: INTERCONNECTION OF DFIGS WITH GRID
5.1 GENERAL
5.2 INTERCONNECTION OF DFIGS
5.3 NORMAL WIND FARM OPERATION
5.3.1 Real Power Flow
5.3.2 Voltage Regulation
5.4 ANALYSIS OF TOTAL HARMONIC DISTORTION
5.5 EFFICIENCY OF DFIG WITH DIFFERENT SUB-SYSTEMS
5.6 CONCLUSIONS
CHAPTER 6: SUMMARY, CONCLUSIONS AND FUTURE WORK
6.1 SUMMARY AND CONCLUSION
6.2 FUTURE WORK
Objectives and Research Scope
This thesis aims to develop and verify a simplified electromechanical model of a Doubly Fed Induction Generator (DFIG) to analyze its performance under transient and short-term voltage stability conditions, while exploring various grid-support configurations to enhance power efficiency and reduce harmonic distortion.
- Electromechanical modeling of DFIG in MATLAB/SIMULINK environment.
- Integration of sub-systems including battery energy storage, buck-boost converters, and specialized transformers.
- Analysis of grid support capabilities through active and reactive power control under constant and variable wind speeds.
- Evaluation of Total Harmonic Distortion (THD) and system efficiency across different DFIG configurations.
Excerpt from the Book
1.1 GENERAL
With the development of societies and comfort life style, the utilization of electric power is increased day-by-day and the gap between demand and supply is increasing around the world. Electric power generation through non renewable power plants leads to polluting the air and also decreasing the fossil fuels. Due to limited fossil fuel resources and large environmental problems caused by them, renewable energy sources like solar power, wind power in particular are developing quickly in the world. Wind energy is one of the fastest growing renewable sources of energy in the world. The generation of wind power is clean and non-polluting; it does not harm the environment. During the last decade use of wind energy has raised substantially, and its share in total energy production has increased to a great extent. There are many countries around the world that are spending on wind projects from the research to installation .Wind energy is a very clean and suitable solution to be one the answers for increasing energy demand.
Summary of Chapters
CHAPTER 1: INTRODUCTION: This chapter introduces the growing necessity of wind energy, its background, and the research objectives regarding DFIG-based systems.
CHAPTER 2: LITERATURE REVIEW: This chapter provides an up-to-date survey of research papers and existing techniques concerning DFIG modeling and control strategies.
CHAPTER 3: MODDELING, OPERATION AND CONTROL OF DFIG: This chapter details the steady-state modeling, transient control algorithms, and reactive power control strategies for the DFIG system.
CHAPTER 4: INTERCONNECTION OF DFIG WITH DIFFERENT SUB-SYSTEMS: This chapter evaluates the performance of the DFIG when integrated with battery storage, buck-boost converters, and various transformer configurations.
CHAPTER 5: INTERCONNECTION OF DFIGS WITH GRID: This chapter analyzes the impact of the DFIG system on grid stability and presents a comparative harmonic distortion and efficiency analysis.
CHAPTER 6: SUMMARY, CONCLUSIONS AND FUTURE WORK: This chapter synthesizes the research findings and outlines potential future improvements, such as cost reduction and optimized voltage regulation control.
Keywords
Doubly-Fed Induction Generator, DFIG, Wind Energy Conversion System, WECS, Battery Energy Storage System, BESS, Buck-Boost Converter, Grid Interconnection, Reactive Power Control, Total Harmonic Distortion, THD, Power Efficiency, MATLAB, SIMULINK, Voltage Regulation.
Frequently Asked Questions
What is the primary focus of this thesis?
The thesis focuses on modeling and analyzing the Doubly Fed Induction Generator (DFIG) to improve grid stability and power quality using various sub-systems such as battery storage and custom transformer configurations.
What are the key thematic areas?
The study covers DFIG modeling, control algorithms, reactive power management, harmonic distortion analysis, and system integration strategies for wind farms.
What is the core objective of the research?
The primary goal is to develop a simplified DFIG model in MATLAB/SIMULINK to study how the generator can provide grid support through precise control of active and reactive power.
Which scientific methodology is utilized?
The researcher employs numerical simulation using MATLAB/SIMULINK to build electromechanical models, perform harmonic analysis via FFT tools, and evaluate performance under variable wind conditions.
What topics are discussed in the main body of the text?
The main body examines steady-state and transient models, control structures for rotor and grid side converters, and the comparative performance of various integration techniques like buck-boost converters and 3-winding transformers.
Which keywords define this work?
The work is characterized by terms such as DFIG, WECS, BESS, Harmonic Distortion, Reactive Power Control, and Grid Interconnection.
How does the buck-boost converter affect the DFIG performance?
The buck-boost converter is used to manage DC-link voltage fluctuations, improving the system's ability to dispatch power and regulating output more effectively than a standard configuration.
Why is the 3-winding transformer highlighted in the results?
The research concludes that the DFIG with a 3-winding transformer achieves high efficiency (above 93%) and effective harmonic management compared to other tested sub-systems, despite the higher cost of implementation.
- Quote paper
- Akshay Kumar (Author), 2014, DFIG-based Wind Power Conversion System Connected to Grid, Munich, GRIN Verlag, https://www.grin.com/document/279068
