Class E/EF Inductive Power Transfer to Achieve Stable Output under Variable Low Coupling

This paper develops an inductive power transfer (IPT) system with stable output power based on a Class E/EF inverter. Load-independent design of Class E/EF inverter has recently attracted widespread interest. However, applying this design to IPT systems has proven challenging when the coupling coefficient is weak. To solve this issue, this paper uses an expanded impedance model and substitutes the secondary side’s perfect resonance with a detuned design. Therefore, the system can maintain stable output even under a low coupling coefficient. A 400 kHz experimental prototype validates these findings. The experimental results indicate that the output power fluctuation remains within 15% as the coupling coefficient varies from 0.04 to 0.07. The peak power efficiency achieving 91%.