Optimized modulation strategy for three-phase dual-active-bridge DC-DC converters to minimize RMS inductor current in the whole load range

This paper proposes an optimized modulation strategy for three-phase dual-active-bridge (3p-DAB) DC-DC converters, which can minimize RMS inductor current and enhance the efficiency in the whole load range, especially under low load situations. Three control variables, two duty cycles and a phase-shift ratio, are introduced in the proposed modulation strategy. A universal analysis for the operating characterization of a 3p-DAB converter is presented using the multi-frequency approximation method. Moreover, the analytical expressions of RMS inductor current and transmission power are deduced. In order to obtain the optimal situation with minimization RMS inductor current, a constrained nonlinear programming problem is established. On this basis, an optimization algorithm, the interior-point method, is applied to solve the problem and derive control variables of the modulation strategy. An experimental prototype is established and the experimental results validate that the RMS inductor current optimization and efficiency improvement are realized by using the proposed modulation scheme.