A novel technique for discrimination of Foreign Object from misalignment in Wireless Charging Systems

Discrimination between foreign object intrusion (FOI) and misalignment between inductive power transfer pads is of great importance due to its impact on the performance of the IPT system. This paper proposes a combinational use of resonant frequency deviation technique and RMS current measurement for foreign object detection and misalignment identification in IPT systems. The paper presents the finite element analysis (FEA) of an IPT system with both FOI and misalignment and a simulation of an 35 kHz series-series resonant IPT system. The results showed that both cases causes a change in the value of the IPT system's primary, secondary and mutual inductances (L-p, L-s, L-m) and a consequent change in the system's resonant frequency. The maximum resonant frequency deviation for the cases of FOI and the misalignment are 660Hz and 74Hz respectively while the region of overlap in resonant frequency deviation is between 8 Hz and 74 kHz. To discriminate between these cases, the simulation results show that for the pad misalignment, a higher primary resonant current is needed to fix power transfer than FOI.