Efficiency-Optimized Modulation Scheme for Three-Phase Dual-Active-Bridge DC–DC Converter

The three-phase dual-active-bridge (3p-DAB) converter features isolated bidirectional power flow, soft-switching capability, reduced transformer, and filter volume. Thus, it is a promising topology for high-power dc-dc conversion. However, when it operates under light load or far from the unitary voltage ratio, the resulting converter efficiency is degraded by the loss of soft-switching capability or increased rms current. To overcome this issue, this article presents an optimized hybrid modulation scheme designed to minimize the total power losses of a 3p-DAB converter under load and voltage variations. An optimization scheme, including switching losses, conduction losses, and core losses, selects the best operation mode for a desired operating point between a novel zero-vector modulation and the traditional phase-shift modulation. An experimental prototype operating at a switching frequency of 100 kHz and a maximum output power of 1 kW was built to validate the theoretical analysis. The results show substantial gain in the converter efficiency, especially at low power or nonunity voltage ratio operating points.