Analysis and equivalent of four-coil and two-coil systems in wireless power transfer

Wireless power transfer (WPT) has attracted widely attention in the last decade, especially in implantable medical devices, electrical vehicle battery charging, the mining equipment, and so on. In a WPT system, the two most adopted structures are two-coil and four-coil configurations. Actually, the four-coil can be equivalent to the two-coil configuration under certain conditions. In this paper, a four-coil structure is equivalent to two different types of two-coil structure at the resonant frequency. The analytical expressions of the equivalent are derived. The simulation and experimental results verify the effectiveness of the equivalent.