Abstract

Large-scale integration of Wind Generators (WGs) with distribution systems is underway right across the globe in a drive to harness green energy. The Doubly Fed Induction Generator (DFIG) is an important type of WG due to its robustness and versatility. Its accurate and efficient modeling is very important in distribution systems planning and analysis studies, as the older approximate representation method (the constant PQ model) is no longer sufficient given the scale of integration of WGs. This thesis proposes a new three-phase model for the DFIG, compatible with unbalanced three-phase distribution systems, by deriving an analytical representation of its three major components, namely the wind turbine, the voltage source converter, and the wound-rotor induction machine. The proposed model has a set of nonlinear equations that yields the total three-phase active and reactive powers injected into the grid by the DFIG as a function of the grid voltage and wind turbine parameters. This proposed model is integrated with a three-phased unbalanced power flow method and reported in this thesis. The proposed method opens up a new way to conduct power flow studies on unbalanced distribution systems with WGs. The proposed DFIG model is verified using Matlab-Simulink. IEEE 37-bus test system data from the IEEE Distribution System sub-committee is used to benchmark the results of the power flow method.

Highlights

  • The results presented in this chapter reveal that the detailed modeling of the Doubly Fed Induction Generator (DFIG) can overcome the inaccuracies of the traditional model used by many utilities to solve the power flow

  • The proposed model accounts for a wind turbine, two VSCs connected back-to-back through a DC link and a wound rotor induction machine (WRIM) (Wound Rotor Induction Machine)

  • It is possible to further expand the model proposed in this thesis by incorporating these detailed losses to get an even more accurate picture of the DFIG

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Summary

Chapter 1

The first section of this chapter provides a brief background of wind electric generators and their scale of integration in power systems. The second section reviews the relevant literature and provides the logic behind the ideas and applications proposed in this thesis. The third section describes the scope and objective of this research and presents the thesis outline

Background
Review of Related Research
Motivation of this research
Chapter 2 Wind Energy Systems
Wind Energy Conversion Systems
Yaw Control
Electrical Power Control and Wind Electric Generators
Structure
Operating Principle
Chapter 3 Proposed Model of DFIG type WG
VSC with DC link Model
Three Phase WRIM Model
Proposed Complete DFIG Model Algorithm
Chapter 3 Proposed Model of DFIG type WG Measurements
Comparison of Results for both DFIG Models
Chapter 4 New Load Flow approach with the proposed DFIG Model
12 Voltage solution
Chapter 4 New Load Flow approach with the proposed DFIG Model Step 11
Integration of DFIG models in Power flow Analysis – Two Approaches
Conventional Power Flow approach with traditional DFIG Model (LF-1)
New Power Flow approach with the proposed active DFIG Model (LF-2)
Validation of Proposed New Approach of Power Flow
Conclusions
Suggestions for Future Research
General equations used in WRIM model and DFIG algorithm
Input Data file for Matlab Power flow program
Main Program file reads the data file and all other function files
Line segments impedance and admittance matrices
Findings
Power Balance Equation Solve function F = myfunfr012(X)
Full Text
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