DAB Converter for EV Onboard Chargers Using Bare-Die SiC MOSFETs and Leakage-Integrated Planar Transformer

This article discusses electrical design optimization of a 3.3 kW, 380 V to 250–380 V, 500 kHz, dual-active-bridge dc–dc converter for onboard chargers, operated with constant-power (CP) charging. In order to operate the converter at 500 kHz without concerns on switching performance and efficiency while also improving power density, a low-parasitics, PCB-based, wire-bondless full-bridge module featuring bare-die SiC MOSFETs and compact, electrothermally multifunctional coolers is employed. High switching frequency operation also felicitates the realization of the DAB inductor using the transformer’s leakage inductance, thereby enhancing the power density by eliminating the need for a discrete inductor. Design strategy for such magnetic integration in a planar transformer is discussed, followed by a systematic design optimization of the transformer, including the selection of leakage inductance value, the core geometry, and the number of turns for achieving zero-voltage switching (ZVS) and maximum average efficiency over the entire charging profile. Experimental validation was performed using a proof-of-concept prototype, which is operated up to 3.3 kW and has a final projected power density of 5.44 kW/L. Results demonstrate the operation with ZVS over the entire charging profile with satisfactory high-frequency waveforms and a peak efficiency of 98%.