Modeling and stress analysis of Doubly-Fed Induction Generator during grid voltage swell

The Doubly-Fed Induction Generator (DFIG) based wind turbine system is presently dominant in the wind turbine market. Due to heavy load switch-off and faults in the power grid, voltage swells may occur and this phenomenon is currently given sufficient insights. This paper starts to describe the DFIG modeling and challenges when facing the symmetrical voltage swell. Then, the High Voltage Ride-Through (HVRT) capability of the DFIG can be calculated by using the demagnetizing current control, and the stator current, rotor current as well as the electromagnetic torque can be deduced during the transient voltage swell and its recovery. It is concluded that although both higher swell level and higher rotor speed cause higher rotor electromotive force, the doubly-fed induction generator can successfully ride through the grid fault due to the relatively small swell level required by the modern grid codes. Additionally, the calculated maximum stresses of the DFIG can be verified by simulation results in terms of the rotor current, stator current, and the torque at various swell levels.