LVRT Control Of The Double-fed Windfarm Via VSC-HVDC Grid-connected System

Large scale wind farms connected with VSC-HVDC transmission system, the electric energy delivery, will become a new form of wind power transmission. Especially in the wind energy resources in China is rich area, due to the limited transmission capacity of the transmission system, wind energy can not be outside send out, resulting in a waste of resources. Therefore, the wind power generator and the VSC-HVDC grid connected wind, large scale delivery, is the future of large scale wind sending a realistic choice. Doubly fed wind turbine wind farm is currently using more models, which has the advantages of high performance price ratio, easy to control etc.. However, the Rotor Doubly fed wind turbine through an AC-DC-AC process, again sent the wind sent the Internet terminal, the stator is directly connected with the power grid, when the power failure, over current and over voltage phenomenon of the system, causing great disturbances of the doubly fed wind machine, easy to cause the fan off network operation of grid connected system, interference, caused very big, can not meet the low voltage ride through.(1)Research on wind unit equivalent method, the number of typhoons machine is equivalent to the single blower, easy controlling wind unit. The principle and control method of doubly fed wind generator, respectively in the three-phase static coordinate and coordinate system, the mathematical model was established; conducts the research to the network side PWM and the rotor side PWM, the establishment of mathematical model, the corresponding at the same time, analyzes its control principle.(2)Mathematical model and control strategy research and fan unit is connected to VSC-HVDC, respectively, in the three-phase static coordinate system and the coordinate system, the mathematical model was established; at the same time to study the design of current control strategy, the outer loop power controller. Because the fan network fault, VSC-HVDC three level structure connected research and fan unit, for the subsequent analysis of the rectifier and the inverter will pave the way for the impact effect.(3)Research on the problem of the fan through the VSC-HVDC low voltage ride through. Mainly for the grid side fault occurs, the fault point voltage drop will occur, the grid side admission functional capacity greatly reduced. However, the wind a chance to continue transmission of electric energy to the system, it will cause the DC side power accumulation appeared, indirect cause of DC side voltage rise, when the failure is serious when, will cause damage to components of rectifier and inverter. Therefore, solving the problem of low voltage fan through a VSC-HVDC grid connected doubly fed wind machine through, from the traditional low voltage through empirical method, based on MATLAB/Simulink simulation platform, build the double fed wind farm by the incorporation of the LVRT model of VSC-HVDC, taking in the DC side of the application method of unloading device, unloading process, the simulation validation the method. At the same time, voltage sag, to study the influence of fault period, the impact of the rectifier and the inverter, provides a theoretical reference for the practical engineering application..