A 6.78-MHz distance-insensitive wireless power transfer system with a dual-coupled L-type matching network

A 6.78-MHz wireless power transfer (WPT) system can achieve a long transmission distance, which is based on magnetically coupled resonant technology. Due to its high quality factor coils, the system performance is greatly affected by position displacement. In this paper, a weakly coupled and distance-insensitive WPT system with a dual-coupled L-type matching network was proposed. To improve displacement tolerance, the proposed system used a dual mutual inductance matching network, which did not require feedback to change capacitance or inductance dynamically. To remain lightweight, printed multi-coils without ferrites were used. To obtain a higher efficiency over a weakly coupled distance, a series of parameters were optimized, i.e., the optimal dimension, the matching distance, and the real center. To verify the output performance in X/Y/Z-axis displacements, a prototype with a maximum output power of 50 W was created, and a DC-DC efficiency of 75%-81% was achieved in a Z-axis displacement of ±15 mm and in an X/Y-axis displacement of ±20 mm.