Three-phase Four-wire Bidirectional Y-converter for an Enhanced Interface between the AC Grid and the Unipolar DC Microgrid

In this paper, a modified three-phase four-wire bidirectional topology is proposed for interfacing the DC microgrid with the AC utility grid. The converter comprises three four-switch buck-boost modules in a star connection, while the neutral of the AC-grid is directly connected to the positive rail of the DC side. This converter permits independent control of each of the three modules, allowing it to endure single-phase faults and adjust to unbalanced conditions. Simulation results are presented for various scenarios, including balanced AC-grid voltages in rectification and inversion modes, unbalanced AC-grid voltages with constant input resistance control, constant input current control, and constant input power control. Finally, a 7-kW experimental prototype is developed to verify the converter’s analysis and simulations. The experimental results show that the converter achieved a peak efficiency of 98.87% and maintained an efficiency of 97.66% at its rated output power. Additionally, the converter exhibited resilient operation, showing stability and reliable performance under both balanced and unbalanced conditions.