A Common-Grounded Single-Phase AC/Bipolar DC Hybrid Microgrid With a Four-Leg Interlinking Converter

Hybrid microgrids (HMGs) are more flexible and require fewer power converters than ac and dc microgrids (MGs); however, the number of wires/buses in HMGs is still considerable, especially when there are multiple voltage levels in the dc subgrid. There are five wires/buses in conventional single-phase ac/bipolar dc (BDC) HMGs, two (phase and neutral) in the ac subgrid, and three (positive, zero, and negative) in the BDC subgrid. This article presents a new four-wire architecture with a common zero and neutral bus for a single-phase ac/BDC HMG that features a new bidirectional interlinking converter (IC). Using the proposed structure, the number of wires/buses and total costs are reduced without increasing the number of IC switches or complicating its control method. Besides, the common zero and neutral bus in the proposed structure provides proper grounding for both subgrids, reduces leakage current (≈0 mA), and improves fault tolerability in dc fault conditions. For this purpose, the dc-side fault ride-through (FRT) capabilities of the conventional and proposed ICs are compared by driving their mathematical models under dc fault conditions. The most severe currents experienced by conventional IC switches in a resistive grounded system are 760 A under positive and 1300 A under negative and zero terminal-to-ground (ZG) fault conditions. However, the proposed IC does not experience any overcurrent in ZG fault conditions, and its switches’ current stresses are reduced to 170 A for positive and 320 A for negative terminal-to-ground fault conditions. To validate the performance of the proposed IC and its modulation technique, simulation results in PSCAD/EMTDC environment and experimental results based on a scaled-down prototype are presented.