Improved hybrid modulation strategy with low solution complexity for dual-active-bridge converters

The dual-active-bridge converter (DAB) is widely used in solid-state transformers. However, its efficiency improvement is always subject to phase shift modulation (PSM) since obtaining optimal results under PSM is difficult. Hybrid modulation provides a solution to this problem. However, present hybrid modulation has not been fully deduced. This paper proposes an improved hybrid modulation strategy. When compared to the traditional method, the proposed strategy has the characteristics of lower solution complexity and greater performance in terms of efficiency improvement. In this paper, the complete derivation process for the proposed hybrid modulation is given and the boundary conditions for different modes of the hybrid modulation are fully discussed. In addition, based on the published losses model, the numerical results of the current stress and total losses under the proposed hybrid modulation, the traditional single-phase-shift modulation, and a previously published triple-phase-shift modulation are compared. Finally, the correctness of the derivation process and efficiency improvement under the proposed hybrid modulation are verified on an experimental prototype.