This paper focuses on the study of a null-flux coil electrodynamic suspension structure for evacuated tube transportation (ETT). A Maglev system in evacuated tubes is a promising concept for high speed transportation systems, and the design of levitation structure is a critical part among the subsystems. The whole system with functions of levitation, guidance, and propulsion is proposed in this paper, and the utilization of magnetic fields from both sides of magnets makes the system simple. The figure eight shaped null-flux coil suspension structure is adopted to provide a high levitation-drag ratio. The equivalent circuit model of the null-flux coil structure is established by employing the dynamic circuit theory. Based on the determination of the mutual inductance between the null-flux coil and the moving magnet, electromagnetic forces are calculated through an energy method. The validity of the dynamic circuit model is verified by comparing the calculation with the 3D finite element analysis (FEM) results, and the working principle of the null-flux coil structure is described. The effects of vehicle speed and the time constant of the coil on the electromagnetic forces are studied at the bottom level of force impulses in one coil and verified by FEM simulation. The characteristics of electrodynamic forces as functions of the magnet speed, the vertical displacements, and the lateral displacements are investigated based on the dynamic circuit theory, and the levitation-drag ratio is compared with that of plate type structure. The results show that the proposed structure is a promising option for application in ETT, and the following study will focus on the dynamic research of the electrodynamic suspension (EDS) system.
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