Reducing Extended Magnetic Stray Field in Wireless Charging Systems of Electric Vehicles

Meeting up the guidelines of international commission on non-ionizing radiation protection (ICNIRP) is critical for wide acceptability of EVs with wireless charging facilities. This paper exploits the concept of magnetic flux cancellation in two mutually decoupled windings of bipolar pad (BPP) to reduce extended magnetic stray field experienced at 80 cm away from the center of the pad. The maximum magnetic flux densities at 80 cm distance of two 7 kW systems, i.e. the traditional two-coil system and the system based on two BPP pads, are investigated firstly by using finite element analysis (FEA) software tool. Simulation results revealed that four-coil system in BPP arrangement can achieve massive reduction of extended stray field, which is 64% lower than that of two-coil system at perfectly aligned position of sending and receiving pad. This would encourage compliance with the safety guidelines of ICNIRP and may pave way for future contributions in the provision of innovative WPT system for high power applications. Experimental results of the four-coil system are provided to verify the concept.