Low voltage ride through technology for variable-speed constant-frequency direct-drive wind power systems

With the rapid increase of the variable-speed constant-frequency wind power in the transmission system,the grid codes are strict with grid-connected wind power system and demand that wind power system should keep connecting with the grid when the grid goes out of order,especially the grid voltage sags.And the direct-drive per-manent magnetic wind power system with full power converter has been demonstrated to have excellent operating characteristics under low voltage.So this paper presents the research of LVRT technology for VSCF direct-drive wind power system.The adverse effects of grid voltage sags on direct-drive wind power system are analyzed firstly.Then combined with existing related standards,the control requirements are proposed to make sure that direct-drive wind power system will succeed in low voltage ride through.Further,other types of low voltage ride-through tech-nology suitable for direct-drive wind power system are summarized,analyzed and compared fully.Finally,the latest progress and the development trend of LVRT technology are given.