Design Methodology for a CLLLC Resonant Dual Active Bridge Converter With Minimized RMS Current and ZVS Operation for Predefined EV Charging Profile

Wide output-voltage operation and bidirectional power flow are important requirements for DC–DC converters in electric vehicle (EV) charging systems, where the battery charging profile is predefined. This paper presents a design methodology for a CLLLC resonant dual active bridge (CLLLC-RDAB) converter that is optimized for a specific EV charging profile under fixed-input voltage, fixed-frequency triple-phase-shift (TPS) modulation. The proposed methodology firstly generates feasible design candidates and identifies the TPS modulation parameters that achieve zero-voltage switching (ZVS) while minimizing RMS currents under all operating points. Evaluating the sum of RMS currents across the profile, the optimal design is obtained. A comparative analysis with conventional designs further highlights the advantages of the proposed method by demonstrating reduced RMS currents across the operating profile. The manufactured 7.3-kW CLLLC-RDAB prototype (100-kHz fixed frequency, 400-V fixed input, 200 – 500-V output) achieves high efficiency of 97.1–97.8% over the entire charging profile. It also exhibits nearly identical efficiency in forward and backward power flow.