Parallel Three-Phase Interfacing Converters Operation Under Unbalanced Voltage in Hybrid AC/DC Microgrid

Parallel interfacing converters (IFCs) with the same dc link are commonly used to handle higher power and currents. In hybrid AC/DC microgrids, they are used to connect ac and dc subsystems, called interlinking IFCs. However, researches on parallel IFCs under unbalanced voltage are quite limited. Considering the adverse effects of unbalanced voltage on a single IFC operation (such as output power oscillations, dc link ripples, and output current increase) and the possibility of aggregation of these effects for the parallel IFCs with common dc link, a novel control strategy for parallel IFCs with various power factors is proposed in this paper. The proposed control strategy cancels out active power oscillation of parallel IFCs, which results in oscillation-free dc link/subsystem voltage. In this paper, a thorough study on the peak current of individual and parallel IFCs is conducted, and their relationship with active power oscillation mitigation is analyzed. Based on analysis, it is proven that under zero active power oscillation, the collective peak current of parallel IFCs is constant under fixed average active and reactive powers. The proposed control strategy keeps the individual IFCs' peak currents in the same phase with collective peak current of parallel IFCs, and thus ensures reduced peak current for redundant IFC.