Research And Optimization Of Magnetic Coupled Resonant Wireless Power Transfer System

Magnetic coupled resonant wireless power transfer(MCR-WPT)is a new kind of power transfer technology.The WPT systems transfer power energy wirelessly through resonant coupling of coils.This technology has the advantages of high transfer efficiency and long distance,and it has a broad application prospect in electric vehicle wireless charging,medical implants,underwater robot etc,so it has become the research focus of the current wireless power transfer technology.This paper focus on the research and optimization of magnetic coupled resonant wireless power transfer system.Firstly,the basic principle of the two-coil wireless power transfer system is analyzed by the circuit theory,the expressions of the output power and transfer efficiency of the two-coil system are derived.On this basis,the basic principle and transfer characteristics of the magnetic coupled resonant wireless power transfer system with four-coil structures are further analyzed,and the advantages and disadvantages of the two-coil structure and the four-coil structure are compared.According to the analysis results,the full series resonant compensation topology with better frequency stability is applied to the research and optimization of the four-coil wireless power transfer system in this paper.Secondly,the output power and transfer efficiency formula of the four-coil model are derived according to the equivalent circuit theory,and the mutual inductance between the coils has a great influence on the transfer characteristics of the system.The mutual inductance calculation method of the circular coils is studied,and the relationship between the distance of the coils,the radius of the coil and the mutual inductance between the two coils is obtained.Then the relationship between the efficiency of the system,the output power and the mutual inductance of the coils is analyzed,and the transfer characteristics of the four-coil system are verified by using the circuit simulation software.Through the study of the relationship between the transfer characteristics of the system and the load resistance,the load value at the best efficiency is obtained.At the same time,the frequency characteristics of the system are analyzed.Then,the theoretical model for dynamic adjustment of equivalent coupling coefficient by the auxiliary coil and its feasibility are analyzed.The auxiliary coils were added between the drive coil and transmitter coil,the receiving coil and the load coil of the four-coil system,the equivalent coupling coefficient of magnetic coupling structure with auxiliary coils is derived,so the four-coil system can dynamically adjust the coupling coefficient between the coils according to the different working conditions,so as to enhance the transfer efficiency and output power of the four-coil transfer system.Finally,an experimental prototype based on the E inverter is built,the feasibility and accuracy of the theory and design method proposed in this paper are verified.The measured peak efficiency of the end to end of the prototype reaches 86%,and when the transfer distance is greater than 150mm,the output power and the transfer efficiency of the prototype can be increased from 20W and 46%to 50W and 60%,without affecting the short distance transfer efficiency of the system,the output power and efficiency of the system can be improved at a far distance.