Foreign Object Detection in Inductive Charging Systems Based on Primary Side Measurements

Abstract

A foreign object detection (FOD) method for inductive charging systems is introduced in this article. The proposed FOD only requires primary side measurements, i.e., primary resonant current and resonance frequency deviation. The proposed FOD incorporates a mechanism for effective discrimination of foreign object intrusion, horizontal and vertical alignment variations of the transmitter and receiver magnetic pads. Alignment variations of primary and secondary magnetic pads as well as intrusion of conductive/magnetic foreign object both impact electromagnetic characteristics, consequently the resonant frequency. FOD for large size objects works properly based on resonance frequency deviation, however, there is the need for discrimination between the FOD for small objects and misalignment. Thereby, both disturbances can be detected by online monitoring of the resonance frequency deviation, and be discriminated from each other by real-time measurement of the primary current. The proposed FOD technique can be added as a protection scheme to the self-tuning controllers of inductive power transfer (IPT) systems operating off its resonance frequency. Finite element analysis along with theoretical formulation of the studied IPT circuit is presented using the proposed method. Conductive FOD method based on frequency deviation and discrimination method using primary resonance current are implemented on an IPT setup, and the experimental results verify its effectiveness in both standby and full-power modes. The test results show that the frequency deviation based FOD method has a high speed in detection of even small scale objects such as a coin.