Study of torque characteristics of DFIG during the voltage sag

In order to analyze the adapt ability of doubly-fed induction generator (DFIG) happens, and achieve the capability of low voltage ride through of DFIG, it is necessary to study the process of electromagnetic transient when the power grid fault happens. In this paper, using the characteristics equation of DFIG, to establish the state space equation of describing the electromagnetic transient process, and derive the analytic rule in the domain time of the current of stator and rotor dq coordinate system when the voltage drop under varying degrees. Therefore, deriving the relationship between the electromagnetic torque of DFIG during the transition mechanism with rotor excitation voltage characteristics, so to provide adequate theoretical basis for protecting the transmission system. In order to verify the correctness of theoretical analysis, the voltage sag transient model of DFIG of 1.5MW on matlab simulation platform is created. The simulation results show that the waveforms of analyzing the transient voltage drop are basically the same, it means the transient analysis is correct. Through the analysis can help to assess the operation characteristics of voltage sag and the design the control technology.