LAUSR

The three-phase dual-active-bridge (3p-DAB) is a popular topology suitable for high-power dc–dc isolated conversion. This converter features bidirectional power flow, zero-voltage switching capability, and reduced transformer and filter volume. These features meet the requirements of several applications, such as solid-state transformers. However, when operating under light load, the resulting converter efficiency is highly degraded by the loss of soft-switching capability. This article introduces the use of a Wye-extended-Delta (Y-$\Delta$e) transformer winding in the 3p-DAB converter, which increases the efficiency under light load, keeping the simplicity of phase-shift control. The framework developed allows a complete analysis of the converter, including the determination of the power and rms current, zero-voltage switching boundaries, and the impact of the selected phase-shifting angle in the transformer design. Additionally, this article presents a negative-sequence modulation scheme, allowing maximum efficiency under light loads to be achieved for both direct and reverse power flows. The performance of the 3p-DAB with Y-$\Delta$e transformers is compared with previously reported winding options for the 3p-DAB. The experimental results show a converter efficiency increase, up to 10% for direct power flow and up to 9% for reverse power flow, when operating at light load (10% of nominal power).