Foreign objects detection is important to ensure safety of WPT system. This paper proposes a state estimation based FOD method. It first builds the model of WPT systems to describe the physical laws during normal operation. When there exist foreign objects on the transmitting/receiving coils, the new model of the system no longer satisfies the physical laws during normal operation. Based on this principle, the detection method gives a foreign object indicator by monitoring the consistency between the measurements and the system model. The mutual inductances and loads are introduced as unknown states to avoid mis-detection of foreign object caused by coils misalignments or loads variations.
