Load matching analysis of magnetically-coupled resonant wireless power transfer

Two basic structures are generally employed in magnetically-coupled resonant wireless power transfer (MCR-WPT), i.e. the two-coil structure and the four-coil structure. The equivalent circuits of these two structures are demonstrated and the expressions of the transfer efficiency, ignoring the source internal resistance loss, are obtained. Two important factors are introduced to facilitate analysis, namely the transfer quality factor and the load matching factor. The larger the transfer quality factor is, the higher the transfer efficiency is. As to the load matching factor, the transfer efficiency varies with the load matching factor and is maximized at a particular load matching factor. The optimal load matching factors, related to the transfer distance, are deduced. To verify the conclusions reached above, both the two-coil and four-coil MCR-WPT systems are implemented, and the experimental results are well consistent with the theoretical calculations.