Doubly fed induction generator based wind turbine systems subject to recurring grid faults

New grid codes demand the wind turbine systems to ride through recurring grid faults. In this paper, the performance of the Doubly Fed Induction Generator wind turbine system under recurring grid faults is analyzed. The stator natural flux produced by the voltage recovery after the first grid fault may be superposed on the stator natural flux produced by the second grid fault, and it may result in large current and voltage transient. The damping of the stator natural flux can be accelerated with a rotor natural current in its opposite direction after voltage recovery, but larger torque fluctuations may be introduced. It may influence the reliability of the mechanical system. An improved control strategy is investigated to accelerate the damping of the stator natural flux in ride-through to prevent the superposing of the stator natural flux, while the torque fluctuations are limited. The performance of DFIG under recurring grid faults is verified by the simulation and experiments.