Soft Switching Over the Entire Line Cycle for a Quadruple Active Bridge DCX in a DC to Three-Phase AC Module: Preprint

This paper is focused on a dc to 3-phase ac module consisting of a transformer-isolated quadruple active bridge (QAB) dc-dc converter, followed by three full-bridge dc-ac inverters. The QAB outputs provide time-varying power at twice the line frequency, which presents challenges in maintaining zero voltage switching (ZVS) on the secondary side during low-power intervals. It is shown how ZVS can be maintained even at zero power transfer using a relatively small circulating current provided by the magnetizing inductances of the high frequency transformers. The approach is particularly effective in high-voltage applications using SiC MOSFETs, where the reductions in switching losses outweigh conduction losses due to the circulating currents. A detailed analysis is presented to address optimum sizing of the magnetizing inductance and determination of QAB dead-times including nonlinear device capacitance effects. The approach is verified by experimental results on a 600V, 5kW prototype where a 50% reduction in total loss is demonstrated, resulting in 98.4% measured full-load efficiency.