Development and validation of model for 95%-efficiency 220-W wireless power transfer over a 30-cm air gap

Although 60-W wireless power transfer (WPT) was demonstrated in 2007, still there is no equivalent circuit model for a submeter air-gap, hundreds of watts, and high-efficiency wireless system. A design-oriented circuit model is needed for this technology to evolve. This paper proposes an equivalent circuit model for the wireless system and analyzes the system based on the proposed model. The proposed model and its analysis are validated by means of finite-element analysis (FEA) and experimental results. Furthermore, as a viable solution for high-power (multikilowatt) applications, losses in the WPT system are investigated in the following section. Because of the high operating frequency (in megahertz), skin and proximity effects were shown to be dominant. A new spatial layout of a coil is proposed that significantly reduces losses caused by skin and proximity effects. With the new spatial layout, i.e., the surface spiral layout, the efficiency and size of WPT system can be improved significantly in high-power applications. The proposed coil design is evaluated by means of FEA.