This paper presents the optimized design of a triple active bridge (TAB) dc-dc converter used in an unfolding-based multiport system to integrate battery storage or renewables with the grid for electric vehicle (EV) battery charging. A low-frequency switched Unfolder is employed for grid interfacing to improve system efficiency; however, it introduces a pulsating dc-link voltage that increases the design complexity, which is addressed in this work. Furthermore, to accommodate a wide EV battery voltage range (200–800 V), a higher-order LCL resonant tank is incorporated to achieve efficient power transfer to the EV port by undergoing soft-switching throughout the voltage range. A power-flow analysis among the different ports is provided, and the TAB tank parameters are optimized to minimize conduction losses and achieve zero-voltage switching (ZVS) for various power-flow scenarios. The proposed TAB converter is experimentally validated using a 5 kW prototype, achieving a peak dc-dc efficiency of 98.51%. The ZVS operation of the TAB is also verified in hardware for EV battery voltages ranging from 200–800 V and for pulsating grid-side dc-link voltages.
