Modeling Of Doubly-Fed Wind Turbine And Research On LVRT Technology

In recent years,wind power still develop rapidly,installed capacity continues to increase,wind power has become an important part of China’s energy structure.The stable operation of wind power and the ability to deal with the failure of power grid is the urgent problem to be solved at present.This paper studies the demand for converter protection during grid failure.The main research work carried out are:The main components of the double-fed wind turbine system are established,including mathematical models of wind turbines,transmission chains,generators and converters.The mathematical model of the two-phase rotating coordinate system is deduced according to the coordinate system conversion method,which lays the foundation for the design and simulation of the subsequent control strategy.The converter control strategy of the doubly fed wind turbine is analyzed,and the corresponding controller model is established.The variation of the parameters of the wind turbine is analyzed empirically.Based on the traditional control strategy,the influence of the stator excitation current on the transient oper ation characteristics of the doubly fed wind turbine is analyzed.The applicability of the improved control under different fault depth is analyzed and the simulation results show that the control method over current has a certain role,but in the deeper power grid failure,the control has some limitations.According to the existing research,a detailed model of the super capacitor overvoltage protection circuit is established,and the charge and discharge characteristics of the circuit and the overpressure protection capability are simulated and analyzed.The simulation results show that the super capacitor protection circuit has good charge and discharge characteristics,and can better suppress the DC bus voltage fluctuation,and provide the overvoltage protection of the unit DC bus during the low voltage fault.In addition,the paper summarizes the supercapacitor capacitance and the line inductance estimation method,and analyzes the influence of the inductance parameter on the charge and discharge current,and provides some guidance for the equipment selection.