An indirect matrix converter based 97%-efficiency on-board level 2 battery charger using E-mode GaN HEMTs

Abstract

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%. Instead of using the regular three-stage design, a matrix converter could directly convert grid AC to high-frequency AC thereby saves one stage and potentially increases the system efficiency, however, the control will be more complex and the high cost of building the back-to-back switches is inevitable. This paper adopts the 650V E-mode GaN HEMTs to build a level-2 on-board charger. The input voltage is 80~260VAC, the battery voltage is 200~500VDC and the rated power is 7.2kW with the bidirectional power-flow capability. Such design saves the bulky DC-bus capacitor. Variable switching frequency is combined with phase-shift control to realize the zero-voltage switching. An active filter is employed to choke the 120Hz output current ripple if needed. To further increase the system efficiency, four GaN HEMTs are paralleled to form one switching module. The overall system efficiency is >97% and the power density is 2.5kW/L with the active filter and 3.3kW/L without the active filter.