A coupling coefficient matching method for WPT system to maintain stable power transfer and high efficiency under wide coupling variations

Abstract

This paper proposes a coupling coefficient matching method for wireless power transfer (WPT) system to maintain stable power transfer and high efficiency under wide coupling variations. The proposed structure consists of two topologies: a detuned Series-Series (S-S) circuit and a detuned Inductor-Capacitor-Capacitor-Series (LCC-S) circuit. By switching between the S-S and LCC-S circuits, four transfer power versus coupling factor (P-k) curves are created, providing stable operating regions to mitigate misalignment effects. With a suitable switching pattern from one mode to another, the system achieves maximum efficiency and delivers stable output power with minimal fluctuations under significant coupling factor variations. A 400-W prototype was developed to validate the theoretical results. Experimental findings demonstrate that when the coupling factor varies within the range of 0.1 to 0.4 (400%), the output power fluctuation is only 3%, and the system efficiency remains between 85% and 95%. The proposed structure does not require special coil design, clamp circuit design, or complex control and can maintain relatively stable output power despite significant misalignment.