A Sensorless Conductive Foreign Object Detection for Inductive Electric Vehicle Charging Systems Based on Resonance Frequency Deviation

A sensorless conductive foreign object detection (FOD) method for inductive power transfer (IPT) systems based on resonance frequency deviation monitoring is proposed. The proposed detection method is based on the fact that the proximity of conductive objects to the transmitter area will affect the resonant characteristics of the system, including resonance frequency. Thereby, the conductive object detection is achieved by constantly monitoring the resonance frequency deviation with respect to its nominal value. Self-tuning controllers for IPT systems are utilized to synchronize the switching power converters with the resonance current in order for the system to operate at the resonance frequency. The proposed method is specifically designed for standby mode FOD in which detection is performed at low power before the entrance of the vehicle to the charging station. Theoretical analysis of the proposed method based on circuit theory and 3D finite element analysis (FEA) is presented. Also, the proposed method is implemented in a case study IPT system and its effectiveness is verified experimentally by detecting different conductive objects. The results show that the proposed method is fast, sensitive, effective, and is capable of detecting conductive objects as small as a 5-cent coin in standby mode.