Study of Fault Current Characteristics of the DFIG Considering Dynamic Response of the RSC

During nonsevere fault conditions, the crowbar protection is not activated and the rotor windings of a doubly fed induction generator (DFIG) are still excited by the ac/dc/ac converter. In these cases, the dynamic response of a rotor-side converter (RSC) has a large influence on the fault current characteristics of the DFIG. In this paper, an analysis method for the fault current characteristics of the DFIG under nonsevere fault conditions is proposed. First, the dynamic response of the RSC is analyzed on condition that the external power control loop is shut down and the reference signals of the inner rotor current control loop are kept constant. Then, the simplified calculation models of the rotor fault current are established according to different design principles of the inner rotor current controller. Based on it, the fault characteristics of the stator current are studied and the analytical expressions of the stator fault current are obtained. Finally, digital simulation results validate the analytical results. The proposed analysis method is applicable for the study of fault current characteristics of DFIG with different control strategies for low-voltage ride through. The research results are helpful to the construction of adequate relaying protection for the power grid with penetration of DFIGs.