Optimal Coil Design for Maximum Power Transfer Efficiency in Resonantly Coupled Systems

Maintaining maximum power transfer efficiency (PTE) is one of the main challenges in resonant inductive power transfer (IPT) systems. Maximum PTE can be achieved if the coupling between transmitter and receiver coils is strong. One way of achieving this is to geometrically optimise a coil by employing small ohmic resistance combined with high self-inductance. In this paper a design method for an optimum coil geometry which offers maximum PTE has been introduced. The proposed technique, in addition to minimising the system's physical size, provides high level of PTE for both strongly- and loosely-coupled links. A design example for a typical IPT system is presented that shows, with a proper selection of strong coupling factor (e.g.: C = 220.), the designed coil geometry can provide maximum PTE of 95.4% for coupling coefficient K = 1. Also, for a loose inductive link with K = 0.215, maximum calculated and measured PTE values are 89% and 86%, respectively.