Research On Control Of AC Excitation For VSCF DFIG Wind Power Generation System

Wind energy is a clean and renewable energy resource. Nowadays, under the stress of energy shortage and environmental pollution, developing wind energy is becoming an important choice to resolve energy and environment problem, the rate of wind generation capacity to the world's power output is increasing expressly. Among all of the wind power generation scheme, doubly fed induction generator (DFIG) is an attractive and booming approach that provides variable speed and constant frequency (VSCF) wind power generation with high efficiency. The thesis is devoted to an in-depth research on the control of AC-excited DFIG for VSCF wind power generation, and designs and develops a laboratory platform dedicated to the research and development of DFIG.An ac excitation converter is inserted in the rotor circuit, the converter need only be rated to handle the rotor power. The rotor excitation currents are changed to realized VSCF running and power control via the converter. Two level voltage source back-to-back PWM converter is used as ac excitation converter for its simple main-circuit and reliable performance, the target of controlling the rotor-side converter is realizing grid-connect, decoupled control of active and reactive power and capturing the maximum wind energy, the task of the grid-side converter are realizing unit power factor and providing constant dc voltage.This thesis analyzes the operation theory of DFIG, then the model of DFIG in synchronous coordinate system is made and analyzed, based on grid voltage oriented vector control strategy a control scheme for grid-connect is designed, after introducing of wind turbine operation characteristics, The maximum power capture scheme by the way of DFIG power control was put forward. According to the control scheme of the rotor-side PWM converter, A Simulation of the system is researched by Matlab/Simulink.Based on the vector control principle, the dq model is used to control the grid-side converter's input current. The dual-close-loop controller of the rectifier in the doubly-fed generating system is analyzed, and the dq model based on current state decoupling and grid voltage compensation control strategy is put forward to develop a grid-side converter. An feedforward control strategy is proposed to improve the resistance of disturbances, in order to get rid of the resonance of LCL filter, a solusion is desigened. In this thesis the process of PI controller design is detailedly introduced, then a model of this converter in Matlab/Simulink is researched.In the end, a laboratory emulation platform used dual DSPs as the control chip is developed, the hardware and software of this wind power generation system is designed. The experimental results testify the validity of the theory and the control strategy proposed by this thesis.