Research On Calculation Method Of Mutual Inductance Between Rectangular Coils In Wireless Power Transfer Systems

Wireless power transmission(WPT)technology gains a wide application prospect in various fields due to its advantages of convenience,reliability,and safety.In recent years,with the further development of the WPT technology,the higher requirement for the systems performances has been put forward in terms of anti-offset capability,transmission efficiency,and electromagnetic shielding capability.However,the misalignment between the transmitting coil and the receiving coil is inevitable in application,which leads to the change of the mutual inductance between the coils,causing the fluctuation of the output power and the reduction of the transmission efficiency.Once the accurate calculation formula of the mutual inductance between coils is obtained,the quasi-constant mutual inductance can be achieved by designing and optimizing the coil structure.Therefore,it is of great significance for improving performance of the WPT system to study the calculation method of mutual inductance between coils.In this thesis,the calculation method of the mutual inductance between rectangular coils is studied.The main works are carried as follows:(1)Considering the difficulty in calculating the mutual inductance between rectangular coils with the misalignment,the calculation formula of the mutual inductance between the non-coaxial rectangular coils is obtained.First,the magnetic flux density of a charged wire is obtained on the basis of the BiotSavart law,and the rectangular coil is equivalent to four charged wire.Then,the mutual inductance calculation formula of the non-coaxial rectangular helical coil is deduced by the subdivision method and the superposition principle.Finally,the results of the mutual inductance calculation formula are compared with the results of the ANSYS Maxwell finite element analysis software and the experimental results.The mutual inductance calculation formula is proved to be effective and accurate.(2)Considering that the calculation method of the mutual inductance between arbitrarily placed rectangular coils with the electromagnetic shielding on one side has not been solved,the calculation formula of the mutual inductance between arbitrarily placed rectangular coils with electromagnetic shielding on one side is deduced.First,the magnetic field of the rectangular coil with the electromagnetic shielding on one side is obtained by the doul Fourier transform and Maxwell’s equations.Then,the space coordinate transformation method is proposed.On this basis,the magnetic flux density in an arbitrary coordinate system is deduced,and the mutual inductance calculation formula of the arbitrarily positioned rectangular coils with the electromagnetic shielding on one side is obtained.Finally,the correctness of the calculation formula is proved by simulation and experiment.(3)Considering the difficulty of calculating the mutual inductance between misaligned rectangular coils with the electromagnetic shielding on two sides,the calculation formula of the mutual inductance between the misaligned rectangular coils with the electromagnetic shielding on two sides is deduced.First,the incident magnetic flux density is obtained by the doul Fourier transform and magnetic vector potential method,which is generated by the current of the rectangular coil.Secondly,the reflected magnetic flux density is obtained by using the Maxwell’s equations and boundary conditions,which is generated by the induced eddy current in the electromagnetic shielding layer.Then,the calculation formula of the mutual inductance between rectangular coils with the electromagnetic shielding on two sides is obtained by using the magnetic flux density method.Finally,the proposed mutual inductance calculation formula is verified by simulation and experiment.