Application of Hybrid Switches (GaN + Si) to the >97%-efficiency 7.2kW Level-2 Charger
While wide-bandgap (WBG) devices have been widely proven effective to reduce the switching loss thereby increasing the switching frequency and shrinking the size of passive components, the high cost of such devices still remain as the hurdle for cost-sensitive industries such as automotive industry. The proposed hybrid approach is to build a hybrid switching power module using gallium nitride (GaN) high-electron-mobility transistors (HEMTs) to parallel with Si MOSFETs. The ultimate goal is to fully utilize merits of both lateral GaN HEMTs (high switching speed thereby low switching loss) and vertical Si MOSFETs (low conduction loss and low cost), which eventually solve state-of-art problems for lateral GaN HEMTs, i.e., low current capability (60A as the maximum), high-reverse-conducting voltage and high cost. The primary application of such hybrid switch is EV battery chargers.
Hybrid Switch Board Using GaN+Si
This project investigates the impact of parasitics when paralleling GaN to Si, particularly on the gate-drive performance, quantifies the crosstalking between Si and GaN gate drivers, and enhances the thermal performance of such module by paralleling Si MOSFETs, and analyzes the economic impact of adopting such hybrid power module in EV chargers. ANSYS is used to optimize the PCB layout, LTSpice is used to simulate the transient in the driver and switching modules, and the physical charger is built to experimentally validate its effectiveness.
How WBG Can Help
Paralleling the ultra-fast GaN to the ultra-cheap Si effectively reduces the cost without compromising the switching performance, shifts the state-of-art power electronics design from "WBG devices are excellent" to "maximizing WBG potentials". Such effort alleviates the suspicion of EV industry on the high cost of WBG devices and expedites the adoption of GaN devices in automotive.
- Liyan Zhu
 Liyan Zhu and Hua Bai, "Transient Analysis in Gate-Drive Loops of GaN+Si Hybrid Switches", IEEE 6th Workshop on Wide Bandgap Power Devices & Applications, 2018;
 Hua Bai, et al, "Critical Short-timescale Transient Processes of A GaN+Si Hybrid Switching Module Used in Zero-voltage-switching Applications", IEEE 5th Workshop on Wide Bandgap Power Devices & Applications, 2017.