Optimal Synergetic Operation and Experimental Evaluation of an Ultracompact GaN-Based Three-Phase 10-kW EV Charger

Fast charging of electric vehicles (EVs) requires isolated ac/dc converters with a wide output voltage range of 200–1000 V. Combining a three-level Vienna rectifier (VR) with four isolated dc-dc dual-active-bridge converter (DABC) modules and latest-generation 600-V GaN technology enables very high switching frequencies of 560 kHz for the VR and up to
$\mathrm {330 {}kHz}$
for the DABCs. Hence, in this article, an ultracompact realization of a 10-kW EV charger module with a power density of 9 kW/dm 3 (about 150 W/in 3), not including the cold plate, is presented. In this context, a simplified DABC modulation method and straightforward yet accurate (confirmed by experiments) loss models for the DABCs and the VR are introduced, which facilitate a thorough investigation of the optimum synergetic operation of the two stages: for the considered converter, changing the VR operating mode from conventional 3/3-PWM (where the two stages operate rather independently, and hence, all three VR bridge legs operate with PWM) to 1/3-PWM (where the DABCs shape the voltage of the shared intermediate dc link, such that always only one of the VR’s three bridge legs must operate with PWM) results in an advantageous efficiency improvement of up to about 2% over a large part of the output voltage and power range and in a peak (PK) efficiency of more than 97%. Furthermore, the synergetic operation of the two-stage system (VR and DABCs) is experimentally verified for the first time, confirming the modeling results and the efficiency advantage of 1/3-PWM (i.e., 95.4% versus 95.1% at the rated load of 10 kW and with 500 V output voltage). Conducted EMI pre-compliance measurements indicate that the change of the operating strategy from 3/3-PWM to 1/3-PWM only requires minor changes of the EMI filter design.