Device and System-Level Transient Analysis in a Modular Designed Sub-MW EV Fast Charging Station Using Hybrid GaN HEMTs + Si MOSFETs

Though wide bandgap devices are believed to be promising candidates for next-generation high-efficiency and high-power-density power electronic converters, two major challenges remain, high cost (more than twice of Si) and less options (the maximum power rating for GaN is only 650 V/60 A). From the device level, paralleling GaN with Si can inherit merits of both GaN devices (superior switching performance) and Si devices (affordable with high-current capability). In this paper, first, GaN HEMTs are paralleled to a TO-247 Si MOSFET to form a high-current switching cell for a 6.6-kW electric vehicle (EV) charging module. A time delay is added between the switch gate signals to make GaN endure the switching loss and Si conduct majority of the static current. Critical dynamic behaviors, such as the current overshoot to the GaN, current distribution during the dead time, and voltage spike during the turn off caused by parasitics, are comprehensively discussed. From the system level, series connecting the input and paralleling output of multiple such modules yield a sub-MW EV charging station. Once one phase drops, the related phase can act as the active filter, while other two phases still work to charge the battery.