Enhanced Control Strategy Based on Virtual Impedance Loops to Achieve the Sharing of Imbalance and Harmonic in 3-Phase 4-Wire Isolated Microgrids

An improved distributed control strategy for imbalance and harmonic sharing in 4-leg droop controlled power converters for 3-phase 4-wire isolated Microgrids is presented in this letter. The proposed control scheme improves a previous one proposed by some of the authors of this letter in the sense that both negative and zero current sequence components are independently controlled. A numerical comparison between the previous method [1] and the presented in this letter shows that, for the studied case, the negative sequence powers shared among the 4-leg converters using the method [1] are: 1638 VA, 2309 VA, 1760 VA, 2610 VA and 1344 VA (these powers are unequally shared). In contrast, with the improved method, all of these powers are equally shared at 1945VA, showing the effectiveness of the proposal. Similar behaviour was verified for zero-sequence powers, which, for the method [1], varied from 1588 VA to 2547 VA, while the proposed approach produced equal sharing of zero-sequence powers (2072 VA) among all the converters.