Five-Degree-of-Freedom Modulation Scheme for Dual Active Bridge DC-DC Converter

A five-degree-of-freedom (5-DOF) modulation scheme is proposed in this article for dual active bridge converter to improve its efficiency in a wide operation range. First, the possible operation modes of the converter under the 5-DOF is analyzed. As a result, 11 effective modes are obtained and their steady-state characteristics expressions are solved, including the inductor root-mean-square (rms) current, inductor peak-to-peak current, and transmission power, etc. It is worth mentioning that the inductor peak-to-peak current expression is simple and it can be regarded as an indicator for rms current. Thus, the peak-to-peak current is treated as the objective to obtain the optimal solutions of each mode, and the global minimum peak-to-peak (GMPP) modulation scheme is obtained. However, there are only two switches that can realize soft-switching operation in the low-power range under GMPP, which results in significant switching loss. Therefore, to further expand the soft-switching operation range in the low-power range, the soft-switching conditions are also taken into consideration, and an optimized five-degree-of-freedom (O5-DOF) modulation scheme is proposed. With the proposed O5-DOF, almost all switches can realize soft-switching operation during the whole load range, and the inductor rms current is minimized simultaneously. Finally, the experimental results are presented to validate the theoretical analysis and effectiveness of the proposed modulation scheme.