Quantitative Analysis of System Efficiency and Output Power of Four-Coil Resonant Wireless Power Transfer

Wireless power transfer (WPT) can achieve safety, convenience, reliability, and suitability for special occasions like mining and implantable medical devices. Resonant WPT (RWPT) has received a great deal of attention in the last decade, through which a large amount of power can be transferred at a relatively long distance with high efficiency. In this paper, the four-coil structure of RWPT is modeled and analyzed. Three important factors are introduced. The analytical expressions of the system efficiency and the output power with a constant voltage source are deduced. The impacts of the source internal resistance, the load resistance, the mutual inductances of the source coil and the sending coil, the sending coil and the receiving coil (related to the transfer distance), and the receiving coil and the load coil are studied, and their optimal values to achieve maximum system efficiency and output power are obtained. The experimental results are in agreement with the theoretical calculations.