1.College of Energy and Power Engineering, Inner Mongolia University of Technology, Hohhot 010051, China;2.School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China

In order to improve the operation characteristics of the direct drive-doubly fed hybrid wind power system under non-ideal grid voltage in a distributed wind power application scenario, a scheme is proposed to realize the flexible fault voltage ride-through in the hybrid distributed wind power system by applying the unified power quality conditioner (UPQC) with a nine-switch converter. Focusing on the control of the nine-switch converter, based on the analysis of the DC-side voltage sharing relationship of the nine-switch converter, the third harmonic injection modulation method for the nine-switch converter is studied to improve the DC voltage utilization rate. Considering the difference in the DC voltage demand of the nine-switch converter, a strategy of dynamically assigning modulation ratio limiting based on the degree of voltage failure is designed. Through the simulation analysis of the above schemes under voltage sag, rise, and harmonics and asymmetrical conditions, the feasibility of the nine-switch converter to optimize the operation characteristics of direct drive-doubly fed hybrid distributed wind power is verified.