Three conventional grid integration methods for DFIG-based wind farms are compared.Start-up control strategies for both modular multilevel voltage source converter based high voltage direct current（VSC-HVDC）system and doubly-fed induction generator are discussed.The modular multilevel VSC-HVDC controller is designed for the reliable integration of wind farms.The proposed control strategies are simulated on the PSCAD/EMTDC platform.And it reveals that the modular multilevel VSC-HVDC system can reliably and effectively realize the start-up and integration of wind farms under different conditions，such as the stable operation condition and variable wind speed condition.