Automatic Resonance Tuning in Wireless Power Transmission System Utilizing Flexible Coil

This article focuses on examining the transmission characteristics of a wireless power transfer (WPT) system that employs flexible coils in folded configuration. The detuning phenomenon resulting from variations in the shape of flexible coil is explored, and a compensation method is proposed. The analysis of dual-coil system operating in LCC-S configuration is conducted through theoretical analysis and numerical simulations to assess the effects of detuning on the transmission properties of system. The findings indicate that the equivalent inductance of coil is diminished by deformation, leading to a degradation of the transmission characteristics as the deformation angle decreases. This deterioration causes the WPT system to transition into the detuned state, thereby reducing the output power and efficiency. To mitigate the impact of flexible coil deformation, an automatic resonance tuning circuit is designed based on the switched capacitance compensation. Adaptive reactance compensation technique is used for the receiver and equivalent capacitance compensation technique is used for the transmitter. Furthermore, automatic resonance tuning circuits are created by integrating a phase comparator and an over-zero detection circuit on the transmitter side. The capacitance value is continuously compensated by adjusting the control signal of the switching tube, ensuring the phase synchronization between the input current and voltage. Finally, the hardware circuit has been designed and the experimental platform has been built. The detuning of 30, 60, 90, 120, and 150 folding angles, as well as the output of the circuit after compensation, have been analyzed, respectively. The experimental results demonstrate that the system can effectively compensate for the effect of coil distortion and improve the output efficiency by at least 20%.