A new control system to strengthen the LVRT capacity of DFIG based on both crowbar and DC chopper circuits

Doubly-fed induction generator (DFIG) is one of important drive systems for wind turbine. It has been widely applied in the power grid today because of its less losses and simpler control strategies. Meanwhile, during voltage dips, the DFIG kept connecting with the grid can provide some reactive power so as to recover the grid voltage, which is called the ability of low voltage ride-through (LVRT). Generally, in the deep voltage sag of grid, a crowbar circuit is set to by-pass the rotor-side converter to protect the whole system. A DC chopper is effective to optimize the responses when the fault occurs. In this paper, the crowbar circuit and a DC chopper circuit are both used to limit the rotor current and DC-link voltage. A control strategy that is used for both of these two circuits is proposed. An index is set to evaluate the effectiveness of the protection. Simulation based on MATLAB/SIMULINK is made to verify theoretical analysis.