Research On Characteristics Of Multi-Coil Magnetically Coupled Resonant Wireless Power Transfer System With Varying Spatial Scales

With the rapid development of modern science and technology,the living style of citizens has also undergone enormous changes and been more convenient,intelligent,green and sustainable.Recently,wireless power transfer(WPT)has attracted an increasing attention because of its security,flexibility and high efficiency.It is an important supplement and innovation of the traditional cable power transmission.Among different kinds of WPT technologies,magnetically coupled resonant(MCR)WPT has become a significant research focus due to its advantages of high transmission power,high efficiency in medium transmission distance and immunity to non-magnetic objects.The basic MCR WPT system consists of two resonant coils(a sending coil and a receiving coil).Previous work had shown that the output power and the transmission efficiency of the two-coil MCR WPT system drops rapidly with the increasing transmission distance.A multi-coil MCR WPT system can be obtained by adding intermediate coils between the sending coil and the receiving coil,which can still reach high output power and transmission efficiency in longer transmission distance.Thus,multi-coil MCR WPT systems were mainly investigated in this thesis.In practical applications,such as pipeline robot,medical detecting capsule and so on,the location of the load coil is usually flexible,which will affect the transmission characteristics of the system.In order to investigate the output power and the transmission efficiency of the coils under varying spatial scales,the equivalent circuit model of the four-coil and the three-coil MCR WPT system was presented,respectively.The relationship between the mutual inductance and the spatial scales of the coils was deduced according to Neumann's formula.As a result,the expressions of system transmission characteristics under varying spatial scales were revealed apparently.Varying spatial scales directly affects the mutual inductance between the coils,causes variation of the output power and the transmission efficiency,and then reduces the stability of the system.To improve the robustness of the system to the spatial scales,on one hand,this thesis proposed a normalization method to design the coil parameters of four-coil MCR WPT system.On the other hand,in three-coil MCR WPT system,we can also obtain stable output power within a specific spatial scale by adjusting the position of the intermediate coil adaptively when the load coil moves.Finally,prototypes of the four-coil and three-coil MCR WPT system had been built in the laboratory,and the experimental results were well consistent with the simulation analysis.The experimental results indicate that stable power output of multi-coil MCR WPT system can be achieved in a specific range of spatial scales by optimizing the coil parameters and the system layout.