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With the increasing popularity of renewable energy and electric terminal equipment, the large-scale application of isolated bidirectional dc–dc converters (IBDCs) is growing. Among these converters, the dual active bridge (DAB) converter, as the core topology of IBDCs, has garnered significant attention due to its bidirectional power transmission capability, simple modularity, and wide soft-switching range. To enhance the efficiency of DAB, various multi-degree-of-freedom (M-DOF) modulation techniques and related solutions have been proposed. However, there is currently a lack of in-depth understanding and thorough comparison of different M-DOF modulation techniques, making it difficult to obtain the optimal solution for different application scenarios. Therefore, based on the latest research and contributions, this article provides an overview of M-DOF, including models, objectives, and algorithms. Furthermore, the existing typical M-DOF modulation techniques are compared through experiments, exploring the differences and advantages among these technologies. Through these analyses, this article offers robust support for the advancement and application of M-DOF modulation techniques in DAB converters.

In modular multiactive bridge (MMAB) converters, which are inherently coupled among dc ports, single phase shift (SPS) control has been widely adopted due to its simplicity in implementation and neglect of coupling characteristics in control algorithms. However, under SPS control, the converter may have unfavorable system efficiency performance, especially when voltage conversion ratios of ports mismatch. To improve the efficiency, this article proposes a common phase shift (CPS) control method for a generalized MMAB or multiactive bridge (MAB) converter. A comprehensive operation analysis of MMAB converters under CPS control with switching characterization of power semiconductors has been carried out. Besides, an overall power loss model is derived, with main electrical components and their power-loss behaviors taken into consideration. Moreover, an optimal strategy aimed at power loss optimization is proposed to improve the efficiency of the converter. Finally, a four-port experimental MMAB converter prototype has been constructed. The experimental results and tested efficiency curves have verified the feasibility and effectiveness of the proposed CPS control.