Coil Research And System Design Of Resonant Wireless Power Transfer

Wireless power transfer system is safe and reliable and convenient when compared with traditional power transmission through electrical wires,especially in some special applications such as medical implants,submarine equipments,and high voltage equipments and so on.Magnetically coupled resonant wireless power transfer is a non-radiative and mid-range wireless power transfer way,and has been widely used in practical applications.However,the transmission efficiency of the magnetically coupled resonant wireless transmission system is easily affected by the parameters of the magnetic coupling coils and their coupling conditions.Additionally,due to magnetic coupling coils working as load of excitation source,it affects the operating characteristics of excitation source.The power transmission efficiency of the magnetic coupling coils will be greatly fluctuated when the distance between the coupling coils is changed,or the metal interference exists around the magnetic coupling coils,and then the loss of the excitation source is increased or even failure.So based on the analysis of the coupling coil parameters,the study of the magnetic coupling resonant wireless transmission system in which the E inverter serves as excitation source,is presented in order to put forward the system design method with the highest efficiency in this paper.The specific content of this paper includes the following three parts:(1)In order to make a quantitative analysis of the power loss in wireless power transfer system,a comprehensive analysis of all the losses of a magnetic resonant wireless power transfer system is presented.The factors affecting the maximum transmission efficiency are studied.The formula of transmission efficiency is derived,and the relationship between the maximum transmission efficiency and coil parameters is revealed.(2)magnetic coupling coils structure is analyzed and optimized.Including the relationship between the internal resistance of the wire the diameter and turn spacing of the coil is studied and the calculation method of self inductance,AC resistance and mutual inductance is analyzed.Design method of coils’ physical parameters are given when restrictions are imposed.The characteristic of the coupling coefficient varying with the distance of coupling coils is discussed and the analytical relationship between maximum transmission efficiency and coil size is derived.The influence of metal objects on the electromagnetic parameters of coupling coils and the maximum transmission efficiency is analysed.(3)The analytical relationship between the equivalent load of E inverter and the coupling coils’ parameters is discussed.The parameters of the wireless power transfer system is designed by combining class-E inverter with theoretical formulas of coupling coils to incresse the overall efficiency.The influence of the surrounding metal on the system performance and system efficiency are discussed.The validity and accuracy of the theoretical and simulation analysis are verified by experiments.