Impact of different transformer-winding configurations on the performance of a three-phase dual active bridge DC-DC converter

This paper investigates the impact of three transformer-winding configurations, i.e. the Y-Y, the Y-Δ, and the Δ-Δ configuration, on the performance of a three-phase dual active bridge (DAB) dc-dc converter. For each configuration, equations for the phase current, power flow, and soft-switching boundaries are derived for all possible switching modes of the three-phase DAB. Thereafter, a comparison is made of the impact on the switches, the transformer and the filter capacitors for the selected transformer-winding configurations. The comparison reveals that the Y-Y and Δ-Δ configuration perform equally regarding above aspects, with the only difference of a lower transformer winding current for the Δ-Δ configuration. The Y-Δ configuration shows a constant commutation current for phase shifts from zero to π/6, therefore, this configuration features a wider soft-switching region for low output powers. Overall, the Y-Δ configuration performs best for power levels between 50 and 80%, regarding the stress on the switches, the transformer, and the filter capacitors. Finally, the theoretical analysis is supported with measurements, obtained from a high-power experimental setup.