Analysis of Capacitive Impedance Matching Networks for Simultaneous Wireless Power Transfer to Multiple Devices

This paper presents wireless power transfer (WPT) characteristics according to load variation in multidevice WPT systems using capacitive impedance matching networks (IMNs). Two basis IMNs of using series-parallel (SP) capacitors and parallel-series (PS) capacitors are used. Four combinations of capacitive IMNs are considered, i.e., SP in a transmitting side and SP in a receiving (Rx) side (SP-SP), SP-PS, PS-SP, and PS-PS. The optimum capacitance values for each IMN are also derived by circuit analysis. For verification, three cases based on the number of Rx coils are considered, and the calculated results are compared with the simulated and measured results for each case. A WPT system for only a single device has identical power transfer efficiency for four combinations of the IMNs. Multidevice WPT systems with the PS IMN in Rx sides are found to transfer more power toward the Rx coil with lower load impedance according to the load variation. On the other hand, using the SP IMN in Rx sides is less sensitive to load variation than using the PS IMN. In addition, a WPT system using the PS-PS IMN combination is less responsive to the cross coupling between Rx coils than that using the SP-SP IMN combination.