A high frequency, high efficiency GaN HFET based inductive power transfer system

This paper aims to develop an Inductive Power Transfer (IPT) system targeting at Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV). IPT systems provide significant benefits over conventional plug-in chargers. However, in order for IPT to be adopted for EV charging, efficiency is a key Figure of Merit (FOM) which needs to be achieved. This paper develops an inverter using Gallium Nitride (GaN) power transistors which have the benefit of low on-resistance and gate charge to reduce the switching and conduction loss. A design methodology for optimising the switching performance of the power transistor is developed in order to minimise switching loss while keeping overshoot under control. An efficiency centric control method is proposed to improve the efficiency of the system, while ensuring sufficient power transfer. The evaluation results show that a GaN based system is capable of outperforming a SiC based system. At a gap of 150mm, the system obtains above 90% efficiency at 1.3 kW. The system efficiency peaks at 95% at 100 kHz operation and 92% at 250 kHz operation at a distance of 80mm for 2kW output power.