Research On Stability Of Grid-connected Wind Turbines Based On UPFC

Wind farms have been increasingly integrated into power systems over the last few decades because of the global energy crisis and the pressure on environmental protection,and gradually going to the road of large-scale and industrialization.When the wind speed is too large or the system has a short circuit fault,the wind turbine exert a relatively serious influence on the stability of the power grid during the grid connection.Its serious consequences include the collapse of the grid,the reduction of the safety and stability margin of the grid,and so on.The stability of wind farms has become a key factor restricting the development of wind power and wind power integration.So the corresponding measures need to be taken to improve the stability of the wind turbine connection.Unified power flow controller(UPFC)as the most powerful,the most comprehensive flexible ac transmission(FACTS)devices,which not only can control active power and reactive power of the system,but also can control the line node voltage amplitude and phase.Therefore this thesis use UPFC to resolve the stability problem of the wind turbines in the process of interconnection to the grid.Fristly,this paper summarizes construction and development situation of the dometic and foreign on the application of UPFC and wind turbine connection.Secondly,selectting the ordinary asynchronous wind turbine which currently caused a greater impact on the stability of the grid in the process of wind turbine connection as a research object,establish its mathematical model,and analyze the stability of the wind turbine in the process of grid connection.Then,according to the structure and working principle of UPFC,the mathematical model of UPFC is established,and its control strategy is determined.On the basis of this,the function and process of UPFC in improving the stability of the system are analyzed.Finally,modeling the wind turbine connection simulation models on Matlab/Simulink simulation platform.Studying the line and wind turbine power,reactive power and voltage fluctuations with/without UPFC when irregular changing of wind speed or the system has a short circuit fault,verifies the regulatory effect of UPFC in the process of wind turbine connection.