Research On The Transmission Characteristics Of Magnetically Coupled Resonant Wireless Power Transfer System

Wireless power transfer means that the energy transmission mode of the power source to the electrical load without direct electrical contact which is achieved by the medium of high frequency power magnetic field,electromagnetic wave,microwave and other physical transmission mediums.Compared with the traditional wired power transfer method,the method of contactless and wireless power transfer is more flexible,convenient,safer and more applicable.At present,microwave radiation,electromagnetic induction coupling and magnetic coupling resonant mode,which rely on microwave and electromagnetic fields as the transmission medium,are more promising.Compared with the other two kinds of wireless power transfer methods,the method based on the magnetic coupling resonance principle has the advantages of high transmission power,high transmission efficiency and long transmission distance.This makes it an important way to achieve the wireless transmission of power in the future,which has attracted the attention of researchers in different fields.The magnetically coupled resonant wireless power transfer realizes the efficient transmission of energy by the magnetic resonance in the near-field range of electromagnetic field.As the output power and transmission efficiency of the system are alwanys affected by the working frequency,load and the coil parameters,the magnetically coupled resonant wireless power transfer system is a nonlinear system with multi parameters cross coupling.Therefore,it is not conducive to the analysis of transmission characteristics and the overall design.In view of the above problems,the research on resonant compensation structures,maximum output power frequency,resonant coil parameters and system design is implemenyed in this paper.The main contents are as follows:Firstly,this paper established the mathematical models of series-series and series-parallel resonant compensation structures based on the theory of mutual inductance for two coils system.Then,the influence of the working frequency,the coupling coefficient and the load on the transmission characteristics is analysised respectively for the two system structures in Matlab.According to the different transmission characteristics of the two resonant compensation methods under the same system parameters,this paper point out the optimal load and transmission distance condition for the two resonant compensation methods.In addition,in order to improve the energy transmission,another resonant coil attached to the two coils system,and then the transmission characteristics of the three coils system is analysised.Secondly,the frequency splitting of the system is discussed by the reference amount of the load voltage.Then this paper analyzes the operating frequency of the maximum transferred power of the system.In the process of analysis,this paper proposes the critical load value based on the relationship between coupling coefficient of the maximum transferred power at the self-resonant frequency and the coupling coefficient when the frequency splitting occurs.According to the relationship between the actual load and the critical load value,the working frequency of the system to maintain the maximum transferred power is analysised under different loads and coupling coefficients conditions.Thirdly,the influence of the inductance parameters of the resonant circuits on the transmission characteristics of the system is analysised.The relationship between the inductance of the transmission coils and the output power,transmission efficiency and the current of the transmission coils are analysised under the condition of a given working frequency.Based on this,the optimal theoretical value of the coil inductance is determined and the solenoid coils that made up of Liz line are made.In addition,the test method of resonant circuit frequency is applying to obtain the accurate coil inductance value by using the signal generator and the oscilloscope.Finally,based on the theoretical analysis of the system and the simulation of transmission characteristics,this paper summarizes the system design scheme based on series-series compensation method,and a magnetically coupled resonant wireless power transfer system is builted.When the transmission distance is 15 cm,the output power of the system is 250 W,and the transmission efficiency is 85.6%.