Compensation of unbalanced impedance of asymmetric wind power PMSG compensated by external circuits in series

The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator (PMSG) compensated by external circuits in series with the 3-phase windings is investigated in this paper. The asymmetric impedance includes the unbalanced resistances, unbalanced self-inductances, and unbalanced mutual inductances. From the perspective of the second harmonic inductances in dq-frame and from the perspective of the second harmonic power, it is theoretically demonstrated that the original asymmetric 3-phase system with asymmetric impedance can be modified to a balanced system by external circuits consisting of resistances and inductances. Therefore, the second harmonic power and DC bus voltage due to the asymmetries can be suppressed naturally without any software modifications. The feasibility of this compensation method is validated by elaborate experiments at different speeds and under different load condition, although the effectiveness might be slightly affected by the non-linearity of the compensation inductance in practice.