Fixed-speed Asynchronous Wind Turbine Model And Transient Stability

With the increase of wind power installed capacity，high penetration leve l ofwind power system has become a great challenge to the safety and reliability of thepower system.Compared with the traditional power system,the stability and powerquality of wind power system are even worse.Wind power changes the power flowof power system,the power on transmission line and the whole inertia of thesystem,and the transient characteristics of wind turbine and power system aredifferent from each other,so that they influence each other when the wind turbineare connected to power system. Fixed-speed asynchronous wind turbine has simplestructure and control strategy,it will lose stability when the grid faults till relayprotection acts and wind turbines are cut off. Also this kind of wind turbine can notcontrol the balance of its active power and reactive power and doesn’t have theability of Low Voltage Ride-Through (LVRT),so that this kind of wind farm can’tmeet the requirement of State Grid about wind farm connected to the grid. Thetransient stability and LVRT of grid-connected wind farms are investigated in thispaper.The wind farms which contain fixed-speed asynchronous wind turbine basedon induction generator are investigated in this paper, and the transient stability ofwind tuib ine models with different masses are investigated in this paper. The windturbines in previous investigation are mostly single lumped mass models, whichneglect the effect of elastic shaft and gear box of the wind turbine mechanicalstructure. The two-masses shaft model is analysed and simulated in this paper,andthe transient stability is discussed.The transient stability of wind turbine includes voltage stability and speedstability. This paper discusses the stability limit of the single lumped mass windturbine and the two-masses wind turbine,deduce the critical clearing time(CCT) ofthe single lumped mass wind turbine and the two-masses wind turbine, andanalyses the effect of CCT with different wind turbine parameters. Simulationresults prove the correctness of the theoretical results.According to the characteristics of fixed-speed asynchronous wind turbine,this paper improves the transient stability of fixed-speed asynchronous windturbine and realize the ability of LVRT.by paralle lling S tatic Sync hro no usCompe nsa tor (STATCOM), Series Dynamic Braking Resistors(SDBR) and usingSTATCOM and SDBR together.Parallel STATCOM can provide reactive power rapidly to wind farms andimprove the terminal voltage partly during the fault,and then make the voltagerecover rapidly after the fault,so that it can reduce the speed of the rotor of generator;SDBR can regulate the active power of wind turbine during thefault,consume the active power that can’t be transported to the grid.So that it canrudece the speed of the rotor and improve the termina l vo ltage greatly,in order toimprove the transient stability of wind turbine. But both two method have theirlimitation,so this paper combine these two methods,presents a method that useSTATCOM and SDBR together to improve the transient stability of windfarms.This method can regulate active power and reactive power of wind farmsduring the fault and after the fault,realize the ability of LVRT,and reduce therequirement of STATCOM.