Abstract
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.
Highlights
With the rapid development of wireless power transfer (WPT), its remarkable flexibility, convenience and portability have been widely used in portable electronic devices, implantable medical devices, drones, smart homes and other fields [1,2,3,4,5]
Foreign metal objects can be divided into non-ferromagnetic metals and ferromagnetic metals according to their own electromagnetic parameters such as electrical conductivity σ and relative permeability μ
In order to investigate the dynamic parameters such as induced current I, the electromagnetic force of foreign metal object F, motion displacement x, its speed dx/dt and acceleration d2x/d2t, the circuit parameters will be introduced into analysis and the nonlinear differential equations will be used to characterize the dynamic process of metal foreign bodies under EMF
Summary
With the rapid development of wireless power transfer (WPT), its remarkable flexibility, convenience and portability have been widely used in portable electronic devices, implantable medical devices, drones, smart homes and other fields [1,2,3,4,5]. The research on EMF is mainly focused on the problems of vibration, noise and mechanical deformation of traditional electrical equipment It has been widely used in electromagnetic forming [13,14], electromagnetic ejection [15,16] and magnetic levitation technology [17]. One of the studied method is reducing the quality factor of the secondary coil [24].In reference [25], a prototype of an electric vehicle capacitive WPT system was built to study the effect of different foreign objects on the system performance when they approached the coupling mechanism from the outside. The characteristics of directional movement of metal foreign bodies under the EMF are studied on the basis of the high-power WPT system.
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