The Study Of AC Excited Variable-Speed Constant-Frequency Wind Power Generation System

With the lack of general energy sources and the worsening of environment problems increasingly,it is provided with very important meanings to abate energy lack by using renewable energy source. Because of its outstanding merits, wind power is paid great attention in the exploitation of renewable energy source, and the wind power technology has become the research hotspot of many country's scholars.The variable-speed constant-frequency (VSCF) wind power generation system using doubly fed induction generator (DFIG) improves the efficiency of wind power. The system can adjust the active and reactive power separately, and improve the stability of electric power system. The key technology of VSCF doubly fed induction generator system is studied in the paper.Firstly, based on the analysis of the dynamic mathematical model of DFIG and its stator-flux-oriented vector control strategy, a dual-closed-loop PI adjuster is designed. Simulation study is carried out on the platform of Matlab/Simulink, the results show the AC excited DFIG wind power generation system can capture the max power energy and realize decoupled control of the active and reactive power.Secondly, comparing two methods of AC-excited DFIG grid-connection control,no-load grid-connection and isolated load grid-connection. The control strategy of DFIG no-load grid-connection is deduced. The simulation results validate the disturbance to the grid is small, and the strategy realize the soft connection between generator and grid.At last, the principle of SVPWM is analyzed and validated. According to power relationship and the demand of AC excited generation system, a dual PWM converter with the capacity of energy bidirectional flow is designed. It also analyzed the basic theory and mathematical model of three-phase voltage source PWM rectifier. The current control with fixed switching frequency and grid voltage forward-fed is used, realizes the control of input power factor at grid side and DC bus voltage. Simulation results show that the converter can satisfy the demand of AC excited generation system, such as low harmonic, high power factor, fast dynamic respond and energy bidirectional flow.