Model-Free Online 4-D Ripple Correlation Control for Loss Optimization of Isolated Quad-Active Bridge Converters

Isolated multi-port converters offer the ability to connect multiple sources and loads operating at different power and voltage levels at their ports, providing galvanic isolation and shared magnetics as benefits. Nevertheless, challenges are present in these converters, primarily due to ports coupling, a high number of modulation variables, and the overall modeling complexity. This paper explores the operation of the dc-dc quad-active bridge converter (QAB) and introduces an optimization approach using an online model-free four-dimensional ripple correlation control (4D-RCC). A fundamental component analysis (FCA) of the QAB is conducted first, resulting in a decoupling matrix that ensures effective closed-loop control for each port independently. Subsequently, the 4D-RCC method is applied to the QAB, allowing online optimization of the converter's overall efficiency. The validation of these analytical findings and the optimization strategy is presented through PLECS simulation results and experimental results obtained from a converter prototype rated 5kW.