| High temperature superconducting(HTS)maglev train technology has ushered in new opportunities with the discovery of HTS materials and the development of maglev technology.However,from the design process of the experimental line,the motor of the HTS maglev is independent of the levitation-guidance system and laid along the line for a long distance,which leads to a significant increase in the system cost.Given the situation,our research group continues to use the magnetic track of the HTS maglev system.It is found that the special-shaped coils can produce longitudinal movement under the same magnetic field of the magnetic track.Based on this,the levitation-guidance-drive schemes for HTS maglev are proposed to generate sustained longitudinal force.The research routes of principle analysis,simulation optimization,and experimental demonstration are adopted.The preliminary scheme is improved from the perspective of optimizing the magnetic field of the vehicle coil and the magnetic field of the magnetic track.First of all,based on the Biot-Savart law,the analytic formula of magnetic induction intensity,which is verified by experimental tests and simulation,is derived.The reasons for the longitudinal displacement of the initial scheme are clarified theoretically.Aiming at the problem of small longitudinal force in the initial scheme,the magnetic shielding scheme is proposed from the perspective of optimizing the magnetic field of the vehicle coil.The simulation and optimization work is carried out from three aspects: the permeability of the shielding material,the combined form of the materials,and the thickness of the shielding body.Based on the optimal structural parameters obtained from the simulation,a finite element simulation model is built to study the influence of the shield on the longitudinal force and the levitation guidance force.The research results show that the magnetic shielding scheme can greatly increase the longitudinal force.When the working height is 20 mm,the longitudinal force reaches 58.3 N.With a load margin of 1.14 KN,the levitation force of Dewar can balance the normal force.The magnetic shielding scheme may apply to scenarios with low load requirements.Secondly,based on Ampere force law,the relationship between longitudinal force and longitudinal differential of magnetic induction intensity is derived.Two experimental schemes are designed to verify the effectiveness.On one hand,the vertical gradient magnetic field of the superconducting magnet is used to simulate the longitudinal changing magnetic field of the magnetic track.The variation trend of the vertical force of the superconducting coil is consistent with the experimental results.On the other hand,magnetic guide plates are added into the coil of the initial scheme,and the fitting calculation and experimental verification of the longitudinal force are carried out.The research results show that the reasonable setting of the magnetic guide plates near the special-shaped coils can produce continuous force.The dynamic experimental results show that the coils produce longitudinal displacement along the running direction of the annular experimental line under the combined action of Ampere force and the inherent magnetic resistance of Dewar.Finally,using the relationship between the longitudinal differential of magnetic induction intensity and longitudinal force,a double-layer magnetic track scheme is proposed.The optimization is carried out on the magnetic track magnetic field and coil size.The simulation results show that the magnetic track with an inclined magnetization angle is conducive to the drive,and the magnetic track with a vertical or horizontal magnetization angle is not conducive to the drive.The optimal magnetic track array consists of three permanent magnets in one cycle,and the magnetization angles are 30°,45°,and 60°respectively.When the vertical height and thickness of the coil are 600 mm and 82 mm respectively,the stable value of the drive is 14.4 N and the overshoot is 1.08%.When the coil length is equal to the length of the permanent magnet track period,the fluctuation degree of the drive curve is the smallest and the stability is the highest.The finite element simulation results based on the optimal parameters show that the magnetic field interference between the double-layer permanent magnet tracks is weak,and each independent subsystem has good levitation,guidance,and driving performances.When the working height is 15 mm,the levitation force of a Dewar is about 1963.20 N;When the current intensity is 30 A and the air gap height is 45 mm,the stable value of longitudinal force is 21.59 N.Compared with the magnetic shielding scheme,the double-layer magnetic track scheme has little effect on the levitation force of the Dewar.Since short magnetic tracks are simulated in this paper,the double-layer magnetic track scheme may be suitable for teaching instruments,demonstration devices,and other application scenarios. |
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