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

TL;DR

This work tackles the instability of inductive power transfer systems under weak coupling by applying a detuned secondary design within Class-E/EF inverters and an expanded impedance model. The approach aims to achieve load-independent operation and stable output despite low coupling coefficients, supported by a 400 kHz experimental prototype. Results show output power fluctuations within 15% and efficiencies up to 91% across $k$ values from $0.04$ to $0.07$, demonstrating practical robustness. The combination of detuning and harmonic-domain impedance analysis provides a path toward reliable IPT implementations in scenarios with variable coupling.

Abstract

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%

Figures (7)

• Figure 1: Circuit model. (a) Basic IPT system driven by class EF inverter. (b) Basic IPT system driven by class E inverter.
• Figure 2: Design flow chat
• Figure 3: $k$-dependent power under proposed design.
• Figure 4: $v_{ds}$ under different $k$.
• Figure 5: Waveform at different $k$: $v_{g}$ (5V/div), $v_{ds}$ (50V/div), $i_{0}$ (2A/div). (a) $k$ = 0.04. (b) $k$ = 0.05. (c) $k$ = 0.07.