Rotor current dynamics of doubly fed induction generators during grid voltage dip and rise

The influence of grid voltage dip on doubly fed induction generators (DFIGs), especially rotor current, has received much attention. So, in this paper, the rotor short-circuit current of based-DFIG wind turbines is considered in a generic way, which is suitable to analyze the cases under different levels of both voltage sag and voltage rise. A direct method is proposed to obtain accurate expression of rotor current. Firstly, the rotor open-circuit voltage in terms of stator flux is determined, and the dynamic equation of the rotor current reduces to a first-order differential equation under rotor short-circuit operation condition. Secondly, the expressions of the rotor open-circuit voltage before and after a fault are obtained, respectively. Finally, based on the obtained expression of rotor voltage, the rotor short circuit currents before and after a fault are obtained by solving the first-order differential equation. This analysis contributes to understand the causes of the problem, and as a result, it helps to adapt reasonable approaches to improve the capacity of the uninterrupted operation of wind power generation during a voltage fault. Simulation results evaluate the proposed analysis.

► We theoretically analyze the rotor fault current of based-DFIG wind turbines using a direct method during voltage fault.
► Accurate expression of rotor fault current is obtained using the proposed method during voltage fault.
► The rotor fault current expression is considered in a generic way, which is suitable to analyze the cases under different levels of both voltage sag and voltage rise.
► The proposed method is simple.