| With the new theory of the wireless power transfer(WPT)technology being proposed and the performances of power electronic device continuously being improved,the long-distance WPT has caused serious concerns of many research teams.While taking place of wire and pantograph,resonant WPT could enhance safety and reliability of power supply system by avoiding the wire abrasion,carbon deposition and the spark in the wire and pantograph.Considering the high transmission efficiency of energy through the resonance method and low loss of high temperature superconductor coils,this paper studies frequency,load,transmission characteristics of the system and influence of structural parameters on electrical performances.Firstly,this paper introduces the three different types of WPT and the basic working principle,illustrates the application advantages of superconducting materials in resonant WPT,gains the value of compensation capacitance based on four circuit topologies and it is found that the compensation capacitance of only SS circuit structure has not influence with the load resistance,the coupling coefficient and the coil parameters.Meanwhile,the coupled-mode theory and its analysis method is introduced to compare the transmission efficiency of SS structure based on circuit analysis and coupled-mode theory,which validates the feasibility of this theory.And formula of transmission efficiency of array-based WPT based on the circuit analysis principle is derived,which illustrates how the parameters influence the transmission efficiency of energy,and the formula indicates that suitable load recesistance and position of receiving coil will improve the transmission efficiency of the system.Secondly,considering nonlinear characteristic of superconductor's conductivity,mathematical expression of its resistivity is derived from formulas of E-J relation,and the critical current density of the superconducting material is obtained by the four-probe method,which will be written in material library to simulate superconductor's performance.In the finite element simulation software based on A-formulation of Maxwell's equations,the structure of different material coils is optimized,3-D simulation mode is established,the influence of load resistance,working frequency and separation distance between transmitting coils on output power and transmission efficiency is studied,and the results show that transmission efficiency reaches the maximum with the appropriate load resistance,and the power is not the best.At the same time,structure of the transmitter with appropriate coil spacing is helpful to the stability of the load power.Then based on this simulation mode,the relation between speed and electrical property of system is studied further in dynamic simulation,and results show that the compact arrangement of the transmitting coils can improve the stability of the load power.Finally,on the basis of the theoretical research and simulation analysis above,experimental platform of the array-based WPT is established,the experimental tests of wireless charging and superconducting coils is carried out to get the testing data of the voltage and current in different circuit parameters(working frequency,duty cycle of electric source and load resistance)and experimental structure(separation distance between every transmitting coils),and analyze the influence of different circuit parameters on efficiency and influence of experimental structure on stability of receiving energy.The experimental results show that the appropriate structure of the transmitting coils in the quasi-static test can make output power of the load resistance at different locations to be stable. |
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