Energy storage based LVRT and stabilizing power control for direct-drive wind power system

To enhance low voltage ride through (LVRT) capability and stabilize output power of direct-drive permanent magnet wind power system, a new type of vanadium redox flow battery (VRB) based energy storage system (ESS) is added at DC-link bus of dual-PWM converters. Correspondingly, the control strategy of bi-directional DC/DC converter is developed to manage the VRB. VRB-based ESS can be used to improve LVRT capability effectively when the grid voltage sags and smooth the grid-injected power when the wind speed rapidly changes. The simulated model is established to analyze the operation characteristics in detail. The results show that the performances of the grid-connected operation are effectively improved for the direct-drive wind power system by using VRB-based ESS at DC-side, and the dynamic response is fast.