Improved grid connection operation of type-III wind turbine under unbalanced fundamental and distorted grid voltages

The paper presents the improved control strategy of balanced and sinusoidal doubly fed induction generator (DFIG) stator current with repetitive control (RC) under grid voltage unbalanced fundamental (the grid voltage fundamental negative component) and unbalanced harmonic distortion (all the harmonic distortion components contain positive and negative sequence). The proposed strategy aims at ensuring balanced and sinusoidal DFIG stator current injected into the power grid. The mathematical modeling of DFIG under unbalanced fundamental and distorted grid voltage is theoretically analyzed, and the repetitive control (RC) regulator is tuned at the multiple of control frequency 100Hz to remove the stator current unbalanced fundamental and distorted sequences. Finally, the availability of the proposed RC strategy is verified by experiment results.