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Isolated multi-port converters can interconnect several sources and loads operating at different voltage levels by their ports, with the advantage of galvanic isolation and shared magnetics. However, challenges exist for such converters, due to coupling between the ports, the high number of modulation variables, and, in general, their modeling complexity. This paper discusses the operation of the quad-active bridge (QAB) and presents its improved operation by a model-free four-dimensional ripple correlation control (4D-RCC). First, fundamental component analysis of the converter is carried out for the QAB, driving a decoupling matrix that ensures good closed-loop control performance for each port individually. Then, the 4D-RCC is presented in the case of the QAB to perform an online optimization of the overall converter efficiency. The presented optimization exploits orthogonal signals for the simultaneous adjustment of the duty-cycles of the four ports of the QAB. The validation of the analytical results and the proposed optimization approach are reported by Matlab/Simulink simulations and experimental results considering a converter prototype rated 5kW.
Ibrahim et al. (2023) studied this question.