A coordinated and steadily fault ride through strategy under short-circuit fault of the wind power grid connected system based on the grid-forming control

Abstract

With the continuous improvement of the penetration level of wind power in the power system, the grid-forming mode of wind turbine will gradually become one of the main modes of system synchronization. The power electronic equipment based on grid-forming control has the ability of frequency dynamic regulation, reactive power voltage regulation, weak current network operation stability and island operation similar to the conventional synchronous generator, however, the problem of strong electromagnetic stress faced by power electronic equipment under grid-forming control will be the key factor restricting the wide application and promotion of grid-forming technology. In particular, the fault ride through problem of the wind turbine under the grid-forming control will face more severe challenges. This paper is based on a switched fault ride through strategy, that is, in case of power grid fault, it is quickly converted from grid-forming control under normal working conditions to the conventional current vector control, so as to facilitate fault current limiting and realize fast dynamic reactive power support. In this paper, a fault ride through optimization control strategy of grid-forming wind turbine is proposed. During the fault, the threshold setting of entering/ exiting the fault ride through control is optimized to form hysteresis control, so as to improve the switching misoperation of control strategy caused by the large fluctuation of grid voltage in the process of fault. Finally, simulation results show that the earlier switching back to the grid-forming control is not the more conducive to the stability of the system, and there is an optimal switching time. The results verify the proposed strategy can effectively improve the transient stability of power system with grid-forming mode of the wind turbine.