The Investigation Of Operation And Control For A Variable-Speed Constant-Frequency Wind Power Generation System

It is of great significance to develop and utilize wind power, which is not only renewable but also without pollution when energy source scarcity and environment pollution are getting more and more serious. Wind power generation technique is improved greatly thanks to that more and more countries all over the world pay attention to it. With the increasing scale of wind power generation system, the investigation on wind power generation technique has been focused on improving the operation efficiency of wind power generation. For this reason, the technique of variable speed constant frequency (VSCF) operation which is capable of capturing the maxim wind power, becomes research hotspot.With the operation and control of an AC excited VSCF wind power generation system as the research subject, this dissertation made complete study by simulation and experiment. The main research contents include: the operation theory of doubly-fed induction generator(DFIG), the maxim wind power capture operation principle, decoupled control of DFIG active & reactive output power, grid-connection control and the study of dual PWM converter.First, this dissertation analyzes DFIG operation theory, including mathematic model of DFIG, coordinate transformation, DFIG operation characteristics, DFIG power relationship, which establishes the theoretical foundation for succeeding study. The second, based on the introduction of wind turbine operation characteristics, The maxim power capture scheme by the way of DFIG power control was put forward, which does not need wind speed measure and can be realized easily with fast dynamic performance and good robustness. The calculation method of the referenced active & reactive power of DFIG was discussed in detail, which aim at the maxim wind power capture and minimizing DFIG copper loss. In order to realize decoupled control of DFIG active & reactive power and to capture the maxim wind power, field oriented vector control technique was applied to DFIG control, A general control strategy based on stator flux oriented vector control was proposed as well. The third, based on the analysis of existent techniques of wind generator grid-connection, this dissertation discusses the grid-connection control principle which fits for the occasion of AC excited VSCF generator, and two kinds of control schemes which can be called grid-connection control with no-load and grid-connection control with isolated load were put forward. At last, the characteristics of dual PWM converter, which is used for DFIG excitation, and the difference between rotor-side converter and grid-sideconverter in control and function aspects was discussed. The control principle of grid-side converter, the function of which is to control the input power factor at grid side and DC bus voltage, was designed on the basis of the field oriented vector control.An integrated simulation model of AC excited VSCF wind power generation system was founded including wind turbine model and DFIG model. By time-sharing method, the grid-connection simulation subsystem and generation simulation subsystem in the model finished the whole simulation progress, which includes grid-connection control and the maxim wind power capture control. In order to make further experimental research, a DC motor was modified to simulate the operation characteristics of the wind turbine and a laboratory experimental system including two DSP and one PC as the digital controllers is built up. Based on these devices, the experimental research of DFIG output active & reactive power decoupled control, the maxim wind power capture operation, grid-connection control and the grid-side converter control were carried out with lots of experiment datum achieved. The experimental results testify the validity of the theory and the control strategy proposed by this dissertation.