Design and Optimization of Planar Magnetics for a Quadruple-Active-Bridge Converter

The broad range of operating points (port loading conditions and voltage levels) in a multi-active-bridge (MAB) converter presents a complex problem in the design of efficient and power-dense magnetic components. It is not feasible to use traditional optimization approaches developed for two-winding transformers, due to the presence of additional design intricacies such as the high number of design and modulation parameters (especially with an increasing number of ports), and the effect of dynamic AC resistance based on port loading conditions. This paper describes a systematic design framework to realize a highly efficient and compact planar magnetic link for a quadruple-active-bridge (QAB) converter. The proposed design framework comprises multi-objective optimization methods for all magnetic components in the high-frequency link, namely, the multi-winding transformer and the series branch inductors. The proposed approach selects the optimal combination of magnetic core geometries, turns ratios, number of turns, branch inductances, and winding interleaving configuration, with the objectives of minimizing the operating pointed weighted efficiency drop and the magnetic volume. Accurate conduction and core loss models are developed to capture loss mechanisms that are distinctive to multiwinding transformers which are verified using finite-element-analysis (FEA) simulations. Finally, a Pareto-optimal magnetic link design is selected and validated for a fully Gallium Nitride (GaN) based QAB converter hardware prototype, achieving a full-power efficiency of 97.8 % at 1 kW.