Research On Over-coupling Power Efficiency Characteristics Of Resonant WPT Systems

With the continuous development and progress of technology,the wireless power transfer(WPT)technology has become a hot research topic at home and abroad.And wireless power transfer technology via magnetic coupled resonances(WPT-MCR),which is widely used in new fields of electric vehicles,implantable devices and so on,has attracted much attention widely owing to its long transfer distance and high transfer efficiency,and has good application prospects and important research significance.At present,WPT-MCR is in its infancy,and there remain some problems that need to be solved,e.g.,the decrease in received power of load as the transfer distance decrease in the over coupled region,and the reason of power decreasing is not clear.Therefore,the characteristics of power and efficiency are analyzed theoretically based on the model of WPT,and the reason of power decreasing is obtained,then the improving methods are proposed.First of all,the principle and component of WPT-MCR were analyzed,then the characteristics of received power and transfer efficiency were analyzed by the coupled circuit method in the over coupled region.The phenomenon that received power of load and transfer efficiency of system decrease was found when the system works in over coupled region.On this basis,we further analyzed the quantitative relationship between received power of load and input impedance,and concluded that input impedance is the decisive factor that affects the received power of load,and impedance mismatch is the essential reason for the power decreasing.Secondly,three methods that improve received power of load and transfer efficiency of system were proposed based on the analysis of characteristics.One is the method of adjusting impedance,which adjusts the input impedance of system by the circuit consisted of non-dissipative components,allowing the system to meet the necessary conditions for maximum transfer power,in order to improve received power of load in the over coupled region.The two is the method of optimizing coil parameters,which analyzes the influence of different coil parameters on energy transfer,the coil parameters that need to be optimized are obtained to improve the transfer efficiency of coils,in order to improve received power of load in the over coupled region.The three is the improving method of power and efficiency,which adjusts the resonance frequency of coils and the operation frequency of source at the same time,not only improving the transfer efficiency of the system,but also improving received power of load in the over coupled region.Finally,based on the simulation model and experiment platform of WPT-MCR,the characteristics of power and efficiency,the reason of power decreasing and the improving methods were verified by simulation and experiments.And the results of simulation and experiments were well consistent with the theoretical analysis,which proved the correctness of the proposed conclusions and the effectiveness of the methods.