Design of an Integrated Solution for Metal-Object Detection and Interference Suppression in CPT Systems

Capacitive power transfer (CPT) technology has been widely studied in unmanned aerial vehicle (UAV) applications due to its advantages of lightweight structure, flexible design, and no eddy current loss. However, metal objects (MOs) can alter the coupler's electric field distribution and circuit parameters, which negatively affects system power factor, output power and efficiency. To detect and suppress the influence of MOs in CPT system, this paper proposes an integrated metal object detection (MOD) and metal object (MO) interference suppression method using an automatic tuning assist circuit (ATAC). Firstly, the impact of MOs on mutual capacitances, input impedance, and output current of the multi-cell single capacitance coupled (SCC) CPT system has been analyzed. Then, an ATAC network is designed on the primary side. By recognizing the DC voltage amplitude of the ATAC network, the impact of MOs on the CPT system can be detected when the CPT system operates in zero voltage switching (ZVS) state. Furthermore, to suppress the interference of MOs, a constant current (CC) output method based on secondary-side resonant frequency tracking was proposed. By recognizing the DC voltage of the ATAC network, the secondary-side resonant frequency in the LC-LC topology can be obtained. At the new operating frequency, the ATAC network adapts the circuit impedance to achieve CC output despite MO interference, while maintaining a high power factor and ZVS characteristics. Finally, an experimental prototype was built, demonstrating that the output current varies within a ±6% range. and the system efficiency reaches up to 80.8%.