Along with the development of offshore wind farm and the application of high voltage direct current transmission technology, the problem of the fault ride through had been serious when the AC side of the wind farm faults. Aiming at it, a new flywheel energy storage system for fault ride through was presented, which was based on modular multilevel converter and dual three phase asychronous motor, and design the controller of the system. The flywheel energy storage system used the modular multilevel converter technology to construct the high power and high voltage converter, and the capacity expansion has been obtained. In order to improve the reliability of the flywheel energy storage system, a dual threephase asychronous motor drive was adopted, and the redundancy had been gained. Then a dual threephase asychronous motor drive control algorithm which could balance the capacitor voltage of each module was designed. At last, based on the MATLAB/Simulink platform, the model of the wind farm and the flywheel energy storage system had been simulated and studied. And the simulation verified the functions of the flywheel energy storage system and the performances of the driven control strategy.