Transient Analysis When Applying GaN + Si Hybrid Switching Modules to a Zero-Voltage-Switching EV Onboard Charger

Abstract

Wide-bandgap (WBG) devices are considered to be a better alternative to silicon switches to realize high-efficiency and high-power-density power electronics converters, such as electric vehicle (EV) onboard chargers. The two major challenges of GaN devices are their relatively high cost (~5 times compared to Si) and much smaller footprint than Si, which though is preferred in the high-power-density application is preferred but brings thermal challenges. Much like SiC is paralleled with Si, and GaN could be paralleled with Si to resolve these challenges. In this article, gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are paralleled to various Si MOSFETs. Two different triggering approaches are considered: one adds a time delay between gate signals and the other uses a pulse triggering technique. Both methods ensure that the GaN endures the switching loss, while the Si switches conduct the majority of the current, thereby maximizing the advantages of both types of switches. To follow is a comprehensive study of the critical transient processes, such as the gate cross talking between Si and GaN, current commutation in the dead band, voltage spikes during the turn-off caused by parasitics, the thermal performance, and the cost analysis. Demonstrated success testing this approach at 400 V/80 A provides evidence that this is a possible approach in the onboard EV battery charger applications. The success of testing under 400 V/80 A makes it possible to an onboard EV battery charger.