Research On Design And Performance Optimization Of Flexible Coil For Electric Vehicle Wireless Charging

Wireless charging technology is of great practical significance for the promotion of electric vehicles.However,conventional wireless power transfer system often suffers from unsatisfactory charging efficiency due to the comparatively longer recharge range and insufficient universality for various car models.Although there are many researches on wireless charging technology for electric vehicles,the reported wireless charging efficiency for electric vehicles can reach more than 80%,the conditions to achieve maximum charging efficiency are often harsh.For example,users need to improve and adjust the parking position to ensure that the receiving coil on the bottom of the vehicle is aligned with the transmitting coil on the ground.Otherwise,the wireless charging cannot be completed or the charging efficiency is greatly reduced,which greatly limits the enthusiasm of the user and hinders the promotion of wireless charging technology for electric vehicles.In view of the above problems,the following researches are carried out in this article:(1)We present a stretchable wireless power transfer(SWPT)system which consists of stretchable inductive coupling coils designed in serpentine shapes that can be adhered to the vehicle roofs to achieve wireless charging.The system integrateds the receiving coil with the roof cover,and the transmitting coil is suspended in the guide rail on the roof,which can adjust the distance from the roof.(2)The basic principle of wireless charging technology is described,the coupling mechanism of wireless charging technology is analyzed,and the factors influencing the coupling coefficient k are confirmed.A physical analysis model of electromagnetic induction wireless charging technology is established,and the efficiency of wireless charging can be optimized by improving the quality factor of the coil.SWPT is introduced,and the various components of the system are analyzed.(3)The calculation model of flexible and stretchable coil is given,the formulas for calculating the inductance and resistance of the coil are obtained,and the influence of the skin effect and the proximity effect on the high frequency AC resistance is analyzed.The magnetic field distribution of the coil was simulated using Maxwell software,and the shape of the coil was determined.The design steps of the flexible and stretchable coil are given,and the geometric parameters of the coil,such as the outer diameter,the number of turns and the line width,are determined respectively.(4)Experiments were performed on flexible coil to test the wireless energy transmission efficiency of the coil on curved surfaces with different curvatures.The results show that the charging efficiencies of the SWPT could keep stable even though the coil are under bending and stretching.As an application demonstration,the SWPT system is installed on the roofs of two different model cars,respectively,and the results demonstrate that the charging efficiencies can keep stable.Then,in view of the problems existing in the experimental testing process,the performance of the flexible and stretchable coil was optimized,and the coil components,serpentine wire were redesigned.the effects of wire thickness,length of straight segment,radius of arc and central angle on the electrical properties and elastic stretchability of serpentine wire are investigated.The results show that the length of the straight segment,the central angle and radius of arc are sensitive parameters affecting the elastic stretchability of serpentine wire.Finally,the sensitive parameters affecting the elastic stretchability and resistance of serpentine wire are optimized by orthogonal experiment.The resistance of the optimized flexible and stretchability coil is reduced by 13.5%and the elastic stretchability is increased by 34.3%.