Soft Switching Region Expansion for Three-Phase Dual Active Bridge based on Phase Shift Design of Wye-Asymmetric Extended Delta Transformer

The three-phase dual active bridge (3p-DAB) converter plays a crucial role in high-power applications due to its superior power density compared to single-phase variants. However, during light load operation, the 3p-DAB can suffer from reduced efficiency due to the loss of soft-switching capability. This paper presents a generalized mathematical model for the three-limb transformer, highlighting the effect of partitioning the secondary phase windings on the transformer's phase shift angle. By dividing the secondary winding into two unevenly distributed sets of windings, the soft-switching region of the 3p-DAB can be improved. The analysis in this paper also utilizes a complex variable stationary reference frame to capture the exact solution of the winding currents, providing a comprehensive understanding of the system behaviour. Furthermore, the paper examines the impact of secondary winding partitioning on the soft-switching region of the 3p-DAB, particularly for the extended delta transformer connection. The insights and analytical techniques presented in this digest can be valuable for engineers and researchers working on the design and optimization of3p-DAB converters, enabling them to enhance the efficiency and performance of these high-power density systems.