Research on the transmission efficiency of different shielding structures of wireless power transfer system for electric vehicles

Abstract

Wireless Power Transfer (WPT) charging system can cause eddy loss on the steel part and the chassis of Electric Vehicle (EV). To study different shielding structures' influence on the transmission efficiency of the WPT system, boundary conditions and assumptions of WPT model in the quasi-stationary electromagnetic field were established and finite element method (FEM) was adopted. The shielding effectiveness of ferrite plate and annular aluminum plate was investigated as well as their effects on 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 same-size area but distributed around the edge of the ferrite. By arranging specialized size annular aluminum plate between chassis and ferrite core, the eddy loss can be effectively shielded and an optimal transmission efficiency was reached with 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.