A combined protection and control strategy to enhance the LVRT capability of a wind turbine driven by DFIG

In order to enhance the low voltage ride-through (LVRT) capability of a wind turbine driven doubly fed induction generator (DFIG) this paper proposes a combined protection and control strategy including the Active Crowbar and Battery Energy Storage System. The conventional crowbar is activated to protect the rotor side converter during the fault interval, premature removal the crowbar will not achieve good purpose of protection for the converter, too late removal will make the motor absorption the reactive power too much from the grid. This problem can be improved by using a control scheme which is auto-switching the crowbar according to the size of rotor current. Furthermore, under fault condition the voltage will ripple in the DC link side, a battery energy storage system (BESS) connected to the DC bus is proposed which is controlled to attenuate the DC voltage ripple via absorbing the redundant power stored in the DC link capacitor. Simulation results show the effectiveness of this combined protection and control strategy.