The Design And Application Of Fault Ride Through Scheme On Doubly-fed Induction Generator

In recent years,the change of wind power generation technology has taken place quickly,the proportion of wind farms in grid is also growing.Therefore,requirements for wind farm system has become more and more strict,the ability of fault ride through(FRT)is stricter than others among them.Doubly fed induction generator(DFIG)has become an important research subject because of its good control performance and power decoupling control.Therefore,this paper has a more detailed study of the DFIG's fault ride through capability.Firstly,researches operation theory and mathematical model of DFIG in this paper,then makes further discussion on DFIG's internal control strategy,analysis the traditional vector control strategy and power regulation characteristics of grid side converter(Grid Side Converter,GSC)and rotor side converter(Rotor Side Converter,RSC),which lays the foundation for further research on how to improve the FRT capacity of DFIG.Then,in order to improve low voltage ride through(LVRT)capacity of DFIG,this paper proposes a new control strategy when the voltage of grid dips.RSC control strategy is: it uses "de-excitation control" on rotor side when the grid voltage drops slightly.The active Crowbar is put into in order to protect inverter safety when grid voltage falls seriously.GSC uses reactive power control mode which can provide reactive power to support network voltage.Finally,the proposed control strategy is applied to "wind farm of Inner Mongolia-Zhengxiangbaiqi-Northlongyuanzheligentu",transforming wind turbines which have weak LVRT capacity and testing them after transformation to verify the effectiveness of the control scheme.During grid voltage drops,wind turbines which have weak LVRT capacity will happen off-grid accident,the response of reactive power compensation device is slow so that the excess reactive power injected into power grid after the fault is cleared,then voltage of grid rise in excess which leads to high voltage off-grid accident.In order to solve this problem,this paper analyzes the causes of grid voltage rises and the transient process of voltage swells,proposing a high voltage ride through(HVRT)control strategy.However,due to the limitation of scene condition,this control strategy is verified by PSCAD/EMTDC simulation software in this paper.