Bai, H., McAmmond, M., Lu, J., Tian, Q. et al., "Design and Optimization of a 98%-Efficiency On-Board Level-2 Battery Charger Using E-Mode GaN HEMTs for Electric Vehicles," SAE Int. J. Alt. Power. 5(1):205-213, 2016, doi:10.4271/2016-01-1219.
Most of the present EV on-board chargers utilize a three-stage design, e.g., AC/DC rectifier, DC to high-frequency AC inverter, and AC to DC rectifier, which limits the wall-to-battery efficiency to ∼94%. To further increase the efficiency and power density, a matrix converter is an excellent candidate directly converting grid AC to high-frequency AC thereby saves one stage. However, its control complexity and the high cost of building the back-to-back switches are barriers its acceptance. Instead, this paper adopts the 650V E-mode GaN HEMTs to build a level-2 on-board charger using the indirect matrix topology. The input voltage is 80∼260VAC, the battery voltage is 200∼500VDC and the rated power is 7.2kW. Variable switching frequency is combined with phase-shift control to realize the zero-voltage switching. To further increase the system efficiency, four GaN HEMTs are paralleled to form one switching module with a novel gate-drive technology. The overall system efficiency is ∼98% and the power density is 3.3kW/L.