Design Of Automatic Impedance Matching In The Resonant Wireless Power Transfer System

The resonant WPT(wireless power transfer)technology,based on non-radiation and near-field coupling, is paid more and more attention by scholars from home and abroad recent years and the technology is implemented between oscillators with same resonant frequency.Compared with magnetic coupling method,the advantages of the resonant WPT lie that loose coupling could make sure longer transmission distance,which may reach dozens of centimeters,even hundred of centimeters and still achieve considerable transmission power and efficiency without requirement of coaxial coupling coils.The problem of impedance matching is very important to promise that output power could be absorbed by impedance in case of being reflected to the source and lead to a demage.An automatic impedance matching system is introduced in the paper and the system could search for the optimal matching point quickly.The following works is mainly studied in the design:1.The principle of WPT is introduced and the equivalent model of two coils and four coils are respectively analysed and as a result,expression of transmission efficiency is concluded. Then make a simulation about efficiency of four coils model with the data actually measured,and model figure expressing the relation of transmission efficiency and distance as well as working frequency is achieved.2.Concept of impedance matching and several kinds of impedance matching networks are introduced,besides,two automatic impedance matching designs are provided and advantages as well as disadvantages are respectively analysed.An automatic impedance matching,namely air capacitor tuning automatic impedance matching system design,which could implement continuous matching is chosen in the design at last.3.The overall structure of the automatic impedance matching system is provided finally,most important of which lies on the following several aspects.?design of double directional coupler?amplitude-phase information detection circuit based on AD8302 design?software design process of the whole system.Traditional impedance matching system depends on the single amplitude of reflection coefficient in combination with matching algorithm to search for the optimal matching result,however,the limit of the algorithm probably lead to system falling to local optimal value and not reaching required convergence effect,or slow rate of convergence.The innovation of points of design lies:?Amplitude and phase parameter of the reflection coefficient in the transmission line are achieved with directional coupler and AD8302 amplitude and phase detecting chip.?The optimal capacitance of the matching network could be calculated quickly with Amplitude and phase these two parameters,then tuning to the calculated most optimal point nearby and using gradient method to search for the most optimal matching point further,which could speed up rate of convergence of matching process and prevent falling into local optimal value.