Research On Control Of Wind Power Grid-connected System Based On UPFC

Under the double pressure of energy and environment,renewable energy power generation based on wind power has received extensive attention,and is gradually becoming large-scale and industrialized.Large-scale wind turbines began to flood into the power grid,and at the same time,the stability of the safe operation of the power grid also suffered a huge threat,which also hindered the further development of wind power,so it is imperative to improve the stability of wind power grid connection.UPFC,as the most flexible and versatile device in flexible AC transmission technology equipment,can not only control system power,but also control system voltage.Therefore,UPFC is introduced into wind power gridconnected system to reduce the impact of wind power access on power grid and improve the stability of wind power grid-connected.On the basis of analyzing the structure and aerodynamic characteristics of different types of wind turbines,the working principle and power generation characteristics of doubly-fed wind turbines are deeply studied.The mathematical model of doubly-fed wind turbines in three-phase static and two-phase rotating coordinate system is built by vector transformation method,and its control strategy is analyzed.The stator voltage oriented vector control and grid voltage oriented vector control methods are adopted for rotor side and grid side,respectively.The simulation model of grid-connected doubly-fed wind turbines is established by Matlab/Simulink simulation platform,and the simulation results are analyzed to verify the correctness and feasibility of theoretical analysis.The principle of UPFC is analyzed theoretically,the mathematical model of UPFC is established,and its control strategy is analyzed in detail.To solve the problem of under-voltage or over-voltage caused by the fluctuation of parallel access voltage and DC capacitor voltage caused by power imbalance in the regulation process of UPFC,the virtual inertia of UPFC DC capacitor is introduced,and the active power and reactive power control loop of its parallel converter are improved.A control strategy of UPFC parallel converter with virtual inertia of DC capacitor is proposed,and its single machine infinite bus simulation model is established by Matlab/Simulink simulation platform.The simulation results show that UPFC can not only adjust the active and reactive power of the system,but also control the fluctuation of system voltage and DC capacitor voltage.Finally,the transient control ability of UPFC to wind power grid-connected system is studied,and the model of doubly-fed wind power grid-connected system based on UPFC is built for simulation verification.The reactive power loss in wind power grid-connected system is calculated through theoretical analysis,so as to determine the capacity value of UPFC,and the influence of different capacity values of UPFC near the determined value on the compensation effect of doubly-fed wind power grid-connected system is analyzed to verify the rationality of the selected device capacity.The effect of UPFC on the stability of grid-connected doubly-fed wind power system under three-phase fault condition is further analyzed in detail.The results show that UPFC can improve the stability of grid-connected wind power generation.