The operation stability of doubly-fed induction generator(DFIG)under weak grid condition has been a focus of research recently. The equivalent input admittance model of DFIG based wind turbine is built in synchronous reference frame. System dynamics

phase-locked loop(PLL)and rotor side controllers including power controller and current controller are considered in this model. The influence of rotor inductance on the system stability is investigated based on the generalized Nyquist criterion(GNC)

which proves that the incensement of rotor inductance has a positive impact on the system stability. PLL is a critical component in the system

which may propagate the grid voltage perturbations to the control system and have an adverse impact on the stability of DFIG based wind turbine system. Compared with the conventional virtual inductance based control strategy

the improved control strategy takes the influence of PLL dynamics into consideration. GNC proves that the proposed method can effectively improve the operation stability of DFIG based wind turbine under the weak grid condition. An 1. 5 MW DFIG based wind turbine detailed model is built in MATLAB/Simulink and simulation results verify the validity of theoretical analysis.