Transmission efficiency of different shielding structures in wireless power transfer systems for electric vehicles

Wireless Power Transfer (WPT) charging systems can cause eddy loss on the steel part and the chassis of an Electric Vehicle (EV). To study different shielding structures' influence on the transmission efficiency of a WPT system, boundary conditions and assumptions of the WPT model in a quasistationary electromagnetic field were established and a finite element method (FEM) was adopted. The shielding effectiveness of ferrite plate and annular aluminum plate were investigated as well as their effects on the coupling coefficient of WPT. It was found that, the setting of ferrite core enhanced the transmission field strength, improved the coupling between two coils, and increased transmit power as well as the actual eddy loss. The actual necessary shielding-area was not confined into the samesize area but distributed around the edge of the ferrite. By arranging specialized size annular aluminum plates between the chassis and ferrite core, the eddy loss can be effectively shielded and an optimal transmission efficiency can breached with an acceptable coupling coefficient decrease. The optimized ferrite bar structure and its EMC characteristics were also studied. It was also found that with equal volume, the optimized ferrite bar structure had better performance in EMC and coupling enhancement than the full ferrite plate.