Research On Long Air Gap Wireless Power Transfer Key Technologies Based On Three-dimensional Magnetic Coupling Structures

With the increasing development of wireless power transfer technology,academia and industry have put forward new requirements for the comprehensive performance of this technology.In order to extend the distance of wireless power transfer,improve the efficiency of the system,strengthen the freedom of system parameter design,and enhance the reliability of the system.The related research works on the long-air-gap wireless power transfer technology based on the threedimensional magnetic coupling structure have been carried out in this article.The coupling coefficient of the conventional magnetic coupling structure decays rapidly with the extension of the air gap between the primary and secondary coils.Therefore,it is difficult to realize enough efficiency wireless power transfer under a long air gap.In order to solve the above problem,a three-dimensional cubic magnetic coupler and an improved cylindrical solenoid coupler for long air-gap wireless power transfer systems are proposed.The application scenario of long air-gap wireless power transfer improves the coupling coefficient and transmission efficiency of the system.The relative distance of wireless power transfer is reflected by proposing a Distance to Diameter Ratio index evaluation method for the relative distance of wireless power transfer under different shapes of magnetic coupling structures.The shape and parameters of the magnetic coupling structure are optimized by the magnetic core longitudinal split method and multi-dimensional finite element evaluation analysis,and the proposed cubic magnetic coupler is compared with the existing various magnetic coupling structures in the long air gap and offset scenarios.Comparisons are made to verify the superior performance of the proposed magnetic coupling structure.Based on the analysis and design method of the cubic magnetic coupler,combined with the characteristics of the solenoid structure,an improved cylindrical solenoid coupler is proposed,which lays the foundation for the follow-up research.In order to promote the digitalization of the power system and accelerate the construction of a high-reliability energy Internet,more and more monitoring and sensing devices are applied to the high-voltage side of smart substations.In order to solve the energy supply problem of the above equipment,a long-air-gap wireless power transfer technology solution based on the cylindrical solenoid coupler and facing the high-voltage post insulator is proposed.The principle of magnetic field confinement to enhance the coupling degree of the magnetic structure through the relay stage is revealed.Through the five-coil series compensation method,a wireless power transfer system based on the equivalent T/S/T compensation network and with constant voltage output characteristics is formed.By moving the position of the primary and secondary auxiliary compensation coils,the output characteristics of the system can be changed.Thus,the degree of freedom of system parameter design is improved.By establishing a system model,the energy transfer characteristics of the system are analyzed.The proposed wireless power transmission system can realize1.5m long air-gap wireless power transmission with the help of hollow post insulators that widely exist in high-voltage substations,and provide power for the condition monitoring devices of high-voltage equipment in the power system.When there is a high voltage difference between the layers of the double-layer three-dimensional magnetic coupling structure,a long loss will occur due to the influence of the parasitic capacitance between the layers.In order to further improve the efficiency of the system,a 2.5m wireless power transfer system based on a distributed series compensation double-layer three-dimensional solenoid magnetic coupling structure is proposed.A design method of the double-layer cylindrical solenoid coupler is proposed,so that the self-inductances of the inner and outer coils of the single-stage magnetic structure are basically the same.The wireless power transmission system based on the multi-stage magnetic coupling structure can supply power to the condition detection device of the high-voltage equipment by means of hollow post insulators with a voltage level of 220 k V.According to the characteristics of the above two-layer cylindrical solenoid coupler,four groups of connection and compensation methods for two-layer three-dimensional solenoids are proposed,analyzed and compared,and the superior characteristics of the distributed series compensation method are expounded.Compared with the two parallel compensation schemes,the method reduces the main loop current of the system and reduces the losses of the inverter module,rectifier module and compensation capacitor.Compared with the centralized series compensation method,this method significantly reduces the voltage between the inner and outer coils,weakens the energy consumption of the parasitic resistance in stray capacitance,and further improves the efficiency.The magnetic field divergence of three-dimensional magnetically coupled structures is stronger than that of planar loosely coupled transformers.The magnetic field is easily affected by surrounding metalware due to the significant magnetic field component in the direction perpendicular to the plane of placement,thereby reducing system efficiency.In view of the above problems,an electromagnetic reconstruction scheme based on ferrite magnetic antennas is proposed to provide shielding and conduction paths for the magnetic field constructed by the three-dimensional magnetic coupling structure.The influence of post insulator aluminum fittings on the WPT system is effectively reduced through the adaptive construction of the magnetic circuit.The electromagnetic reconstruction scheme is oriented to the composite system constructed by the post insulator and the long-air-gap wireless power transfer system based on the three-dimensional solenoid.The negative impact of flanges on the efficiency of wireless power transfer system is weakened.First,the negative effects of aluminum flanges on the magnetic field distribution in the actual system are analyzed from the aspects of coupling weakening and eddy current loss.Next,the suppression effect of the electromagnetic reconstruction scheme based on ferrite magnetic antenna on the above effects is proposed and analyzed.In addition,the parameters of the electromagnetic reconfiguration scheme are optimized,and an equivalent system model is established to explain the effect of the proposed scheme from the perspective of circuit parameters.Finally,based on the real object of the aluminum flange,the feasibility of the proposed scheme is verified by experiments.