Contents I. Introduction
WIND energy is an effective way to deal with the energy crisis and environmental problems [1] –[2] . With the increasing penetration rate of the wind power generation in power system, the doubly-fed induction generator (DFIG)-based wind turbine (WT) has been generally used in numerous wind power generation system due to the independent power regulating capability, variable speed constant frequency operation and low rating converter [3] –[4] . However, limited by the distribution of the wind energy, the large-scale DFIG wind farms are usually located in the remote areas, which connected grid via long transmission lines, the short circuit ratio (SCR) of the system is lower [5] –[6] . The standard of low voltage ride through (LVRT) for existing grid code is based on the strong power grid [7] . Therefore, when the severe fault occurs in the weak grid, the traditional LVRT strategy of WTs may not conducive to maintaining voltage stability of the point of common coupling (PCC) and the system has a risk of the small signal instability [8] . In addition, due to the weak grid severe fault, the wind farm approximate island operations, therefore, the dynamic performance of the DFIG WTs during the weak grid fault may cause the WTs losing synchronism with the power grid. Therefore, the dynamic stability of the DFIG WTs during weak grid fault should be further investigated.
