Voltage Harmonics Optimization for Weak Grid-Tied Doubly-Fed Induction Generator With the Capability of Suppressing Current Harmonics

Suppressing current harmonics is an essential capability of the grid-tied doubly-fed induction generator (DFIG). For the weak grid tied DFIG, the suppression of current harmonics is accompanied by the compromise of voltage harmonics at the point of common coupling (PCC). Currently, the effect of current harmonic suppression is the focused concern. But, the potential of voltage quality optimization is neglected. The key to solving this issue is to find the reconcilability of the conflict between the current quality and voltage quality. Therefore, this paper firstly analyzes the coupling relationship between voltage harmonics and current harmonics at PCC from the perspective of harmonic impedance, and then investigates the optimal harmonic impedance of weak grid tied DFIG, which sacrifices minimum voltage quality to achieve current harmonics suppression. Further, a self-regulated harmonic impedance reshaping for DFIG based on the optimal harmonic impedance design is proposed. The proposed method can adaptively reshape the DFIG impedance to be optimal under different grid conditions. The theoretical analysis and experimental results are done to verify the correctness of the optimal harmonics impedance theory and the validity of the proposed control strategy.