Because of the noncontact structure of wireless power transfer (WPT) systems, foreign metal objects can easily enter into the coupling region—and often move under the action of electromagnetic force (EMF), instead of staying relatively static, which brings a difficult problem for foreign object detection technology. In this paper, we investigate the motion state of foreign metal objects with different properties under the action of electromagnetic force in the coupling space of WPT system. The equivalent model of the circuit parameters with the intervention of foreign metal objects and the differential equations for the motion of foreign metal objects are derived. Combined with finite-element simulation calculations, the motion characteristic of ferromagnetic and non-ferromagnetic metals under EMF was analyzed. The results show that, due to the size and properties of the metal, non-ferromagnetic foreign metal objects have four states: vibration, suspension, static and flying out. The ferromagnetic foreign metal objects will adsorb on the coil surface and rapidly heat up. By establishing an experimental prototype, the analysis uses high-speed acquisition equipment to obtain the movement of foreign metal objects which verified the correctness of the simulation. This research is also beneficial to the operational safety and reliability of the WPT.

In the high-frequency electromagnetic field, the coupling of the wireless power transfer (WPT) system is affected by the electromagnetic force (EMF). The fault conditions will strengthen the influence, cause the damage of magnetic shielding structure, coil deformation, insulation damage and so on. In order to ensure the safe and stable operation of the WPT system, it is necessary to study the local EMF distribution of the coupling mechanism under the fault condition of WPT system. In this paper, the series to series (SS) compensation structure is taken as an example to analyze the changes of electrical parameters of WPT system under typical faults, and determines that the open load fault has the greatest impact on the system. The WPT system with groove-shaped magnetic shield structure is selected as the research object. Establish a mathematical model for calculating the EMF of the WPT system combining the field-path coupling time-step finite element method and the Maxwell stress method, the distribution law of local EMF of magnetic shielding structure when the load is open is analyzed and calculated. At the same time, an experimental platform is built to verify the effectiveness of the method. According to the distribution characteristics of EMF, the smoothing scheme based on variable-turn-pitch planar coil is proposed. The new coil structure obtained by the SNOPT algorithm, compared with the equi-turn-pitch planar coil, the overall force on the coupling mechanism of transmitting end under the open circuit fault at the receiving end is reduced by 86.24study provides a theoretical reference for the optimal design of coupling mechanism of WPT system.

The use of wireless charging technology to charge electric vehicles not only achieves the purpose of safety and convenience, but also reduces the battery capacity of electric vehicles. In this paper, the electromagnetic exposure problem of electric vehicle wireless charging system is taken as the research object, the equivalent circuit model is established, and the analytical formula of output power and transmission efficiency is solved. At the same time, the magnetic field distribution characteristics are obtained. Finally, a set of electromagnetic exposure measurement methods for electric vehicle wireless charging system was proposed, and the electromagnetic exposure experiment of mouse immune system was carried out. Combined with relevant electromagnetic standards, it was concluded that the electromagnetic field did not affect the mouse immune system under the experimental conditions.

Wireless power transmission technology avoids the problem of towed wires in the process of using electric energy, and increases the flexibility of using electricity. It is a hot research topic at present. In order to improve the system performance, a field-circuit coupling algorithm is proposed to analyze the system performance, with the help of the concept of supercomputing. Frequency splitting is a phenomenon in wireless power transfer (WPT) system when the coupling distance is less than the splitting point, the load power changes from a single-peak curve to a double-peak curve driven by two non-intrinsic resonant frequencies. Asymptotic coupled mode theory (CMT) method is used to analyse the frequency splitting phenomena in WPT system. It provides detailed information about interaction of field strength under different coupling states through coupled solution of FEM and CMT. Over coupling, critical coupling and under coupling are three typical states classified by frequency splitting. Experimental results are acquired by two helical resonators. The overall system reaches the critical coupling state when resonators space 1.5 m and the total power on the load is 110 W. Therefore, it is an efficient way to forecast transmission characteristics by using this method.