Bidirectional H8 AC-DC Topology Combining Advantages of Both Diode-Clamped and Flying-Capacitor Three Level Converters

A three-level bidirectional AC-DC converter with H8 topology is proposed to combine the advantages of both neutral-point clamped and flying-capacitor three-level converters for medium voltage AC-DC solid-state transformer applications. The innovative H8 converter features self-balanced capacitor voltage, common-mode voltage elimination, and small capacitance of the flying capacitors. The proposed carrier-based modulation enables the H8 converter to operate under both active and reactive power conditions. A 10 kVA AC-DC converter prototype with 1.7 kV SiC MOSFETs and 3.3 kV SiC diodes verifies the feasibility and advantages of the proposed topology and the modulation method. The capacitance of the flying capacitors in the H8 converter is reduced by 45 times compared to that of the flying-capacitor converters. The H8 converter efficiency is tested up to 99% at 2 kV DC voltage. The proposed H8 converter is suitable for the next-generation PV inverter, grid-forming inverter, MV fast charger, and SST applications.