Research On Power Conversion And Optimal Control Of Variable Speed Wind Power Generation System

This thesis focuses on converter and maximum wind energy extraction control strategies for achieving the highest energy output of variable speed wind turbine power generation systems. Power electronic converters and controls provide the basic platform to accomplish the research of this thesis in both hardware and software aspects.In order to send wind energy to a utility grid, a variable speed wind turbine (VSWT) requires a power electronic converter to convert a variable voltage and variable frequency source into a fixed voltage fixed frequency supply. Generic single-phase and three-phase converter topologies, converter control methods for wind power generation, are introduced in the thesis for establishing variable-speed wind energy conversion systems.Variable speed wind power generation system modeling and simulation are essential methods both for understanding the system behavior and for developing advanced system control strategies. Wind generation system components, including wind turbine, 1-phase IGBT inverter, 3-phase IGBT inverter, synchronous generator, and rectifier, are modeled in this thesis using MATLAB/SIMULINK. The simulation results have been confirmed by field test results. Since the dynamic time constants for these individual models are much different, a creative approach has also been developed in this thesis to combine these models for entire wind power generation system simulation.Generic power electronic converters can possibly extract maximum wind energy only in the medium and high wind speed range when the generator output voltage is sufficient and the system is in rated power. In research into maximum power extraction strategies for low wind speeds, five power electronic topologies, namely uni-directional converter, double voltage rectifier, dc-link boost chopper, Multi-level matrix converter and Z-source converter have been proposed. These strategies are described, analyzed, and tested in this thesis research. Significant improvement in wind energy output provided by these innovations has been confirmed through both computer simulations and field test results.An advanced maximum wind energy extraction strategy relies not only on proper system hardware design, but also on sophisticated software control algorithms. Maximum wind power extraction algorithms for VSWT systems have been investigated, developed and presented extensively in journal and conference papers in recent years. Although these algorithms are based on different power conversion hardware structures, the principles of these algorithms can be roughly classified into three types, namely tip-speed-ratio control, power signal feedback control, and hill-climb searching control. Based on advanced hill-climb searching control, an intelligent maximum wind energy extraction control algorithm is proposed in this thesis. This algorithm has a unique on-line adaptation and optimization capability, which is able to achieve maximum wind energy conversion efficiency through continuously improving the performance of wind power generation systems. This algorithm is independent of wind power generation system characteristics, and does not need wind speed and turbine speed measurements. Therefore, it can be easily implemented into various wind energy generation systems with different turbine inertia and diverse system hardware environments. In addition to the detailed description of the proposed algorithm, computer simulation results are presented in the thesis to demonstrate the advantage of this algorithm. As a final confirmation of the algorithm feasibility, the algorithm has been implemented inside a power IGBT inverter, and tested with a wind simulator system in research laboratory. Test results were found consistent with the simulation results.The wind power generation system based on power converter rapidly becomes a key branch of wind power. Using advanced invert and control technology, the system could be operated at maximum power point under different wind speed. The novel wind energy conversion system has high efficiency, fast dynamic response.