Investigation on control of three-phase grid-connected inverters under unbalanced grid voltage conditions

This paper proposes a novel control scheme of three-phase grid-connected inverters (GCIs), in which a proportional plus resonant (PR) regulator is adopted. The PR regulator, which is tuned at the synchronous angular frequency, can be applied in the stationary αβ reference frame directly. Furthermore, the PR regulator does not require any decomposition of positive- and negative-sequence currents. It will improve the performance of the grid-connected inverters during the transient process of the unbalanced grid voltage fault condition, and its fault ride through capability will be enhanced as well. Compared with the conventional PI control scheme and dual-PI control scheme, the correctness of the theoretical analysis and the feasibility of the unbalanced control scheme with the PR current regulator are validated by detailed experimental tests.