In view of the problems such as big generator amount and limited tower space existing during the traditional wind farm low voltage ride-through（LVRT） update reform， a new dynamic voltage restorer（DVR） topology based on modular multilevel converters（MMC） is proposed which can improve LVRT capability of wind farms by injecting a complementary voltage at the point of common coupling（PCC） while the grid voltage sags. Related control strategies and the modulating method are also proposed. PSCAD/EMTDC simulations are carried out to prove the correctness and effectiveness of the proposed topology and the related control strategy.