Fundamental Research On Double-Sided Air-Cored Superconducting Maglev Linear Synchronous Motor

Maglev train has the advantages of high speed,strong climbing ability,low noise,excellent smoothness and low maintenance cost,etc.It has been widely concerned by scholars at domestic and overseas for a long time.The fundamental principle of levitation is to use magnets to generate a powerful attraction or repulsion force to levitate the train,and the propulsion force generated by linear motors drives the train forward.The train with attraction principle is represented by the German normal conduction electromagnetic suspension(EMS)train,and that with repulsion principle is represented by the Japanese superconducting electrodynamic suspension(EDS)train.Compared with normal conduction EMS,superconducting EDS has the advantages of large levitation air gap,self-stabilization and simple structure,and it has developed into an ultra-high speed mass transfer system.Double-sided air-cored superconducting maglev linear synchronous motor(DSAC-SMLSM)is the motive source of superconducting EDS system,however,little research on it has been reported in domestic and international literature.This paper takes this motor as the research object,and through theoretical analysis,numerical calculation and experimental verification,the research focuses on the motor mathematical model,electromagnetic force characteristics,electromagnetic torque characteristics,armature magnetic field harmonic analysis and suppression,and armature winding AC loss calculation.The superconducting excitation magnetic field of DSAC-SMLSM is a dispersive magnetic field,and the magnetic field distribution at different locations in space is quite different,so the mastery of the superconducting excitation magnetic field harmonic analysis method of such motor is the foremost problem to be solved.A novel analysis method based on double Fourier and coil segmentation is proposed in this paper to deal with the lack of harmonic analysis method for race-track-shaped superconducting coils,which can be used to solve the harmonic magnetic field generated by arbitrary air-cored coils,and its accuracy is verified by 3D FEM and the built magnetic field measurement platform.To address the problem of the low accuracy of the calculation formulas for self and mutual inductance of rectangular-shaped and race-track-shaped air-cored coils,the proposed method is used to derive the calculation formulas with high precision,and its accuracy is verified by measurement results.Based on the results of superconducting excitation magnetic field analysis,combining the bogie coordinate system and ground coordinate system transformation equations,the mathematical model of DSAC-SMLSM is established,including the expressions of superconducting excitation flux linkage,noload back EMF,3D electromagnetic force,3D electromagnetic torque,and the voltage equation,force equation and torque equation of the motor.The correctness of the mathematical model is confirmed by the static thrust test platform built and the no-load back EMF experiments completed by the superconducting EDS test line built by the Aerospace Research Institute.The work above lays the theoretical foundation for the subsequent establishment of the mathematical models for the electromagnetic force characteristics,electromagnetic torque characteristics,armature magnetic field harmonic analysis and armature winding AC losses of the motor.Taking into account that the train bogie is not like conventional linear motors in which the movers can only move in a single direction along the guide rails,this paper investigates the 3D electromagnetic force characteristics and 3D electromagnetic torque characteristics of DSAC-SMLSM.Firstly,the mathematical relationship between dqaxis current,3D electromagnetic force and 3D electromagnetic torque is established to clarify 3D electromagnetic torque generation conditions and main impact factors to provide theoretical basis for motor control.The fluctuation law of 3D electromagnetic force and 3D electromagnetic torque of the motor is analyzed to provide the theoretical basis for reducing the fluctuation of electromagnetic force and electromagnetic torque.Secondly,based on the equivalent circuit of DSAC-SMLSM,the change of armature current of two single-sided air-cored superconducting maglev linear synchronous motors is investigated when the bogie is in deviation or deflection motion.Finally,using the established mathematical model of the motor,the changes of 3D electromagnetic force and 3D electromagnetic torque are analyzed in detail when the bogie is in zero flux position,when vertical displacement occurs,when lateral displacement occurs,and when both vertical and lateral displacements occur,and the results are verified by test data from the Yamanashi test line in Japan.The maintenance of superconducting magnets in a superconducting state is an essential prerequisite for the reliable operation of trains,and for this reason,the method of suppressing armature magnetic field harmonics is investigated in this paper.Firstly,the armature magnetic field harmonics distribution law of the single-layer armature winding scheme is investigated,the effect of the armature magnetic field harmonics on the 3D electromagnetic force of a single superconducting coil is analyzed,and the 3D analytical model of the eddy current loss of the superconducting magnet outer vessel is established.Secondly,to study the method of suppressing armature magnetic field harmonics,the armature magnetic field harmonics of the traditional double-layer armature winding scheme and its effect on the 3D electromagnetic force of a single superconducting coil are analyzed,and the advantages and disadvantages of the scheme are summarized.It is revealed that the biggest drawback of the traditional double-layer armature winding scheme is the low thrust density,and in order to tackle this problem,a new double-layer armature winding scheme is proposed in this paper.Then,based on the design idea of the new double-layer armature winding scheme,a set of schemes to suppress the main unfavorable harmonics of the air gap magnetic field is proposed for different poles slots with different structures of double-sided linear synchronous motors.Finally,the applicability and effectiveness of the proposed scheme for reducing the main unfavorable harmonics of the motor air gap magnetic field in bilateral linear synchronous motors with different structures is fully verified by the magnetic field measurement results of the double-layer air-cored coil and a series of comparison experiments of the two double-sided linear permanent magnet synchronous motors.The armature winding of DSAC-SMLSM is completely exposed to the strong magnetic field generated by the superconducting coil,and a large amount of eddy current loss is generated in the winding wire when the relative motion of the two occurs,in order to reduce the system operating cost and suppress the temperature rise of the ground armature coil,research on the AC loss of the armature winding is carried out in this paper.Firstly,the distribution law of superconducting excitation magnetic field is analyzed in detail by using superconducting excitation magnetic field harmonic analysis method.Secondly,with the major objective of increasing the electromagnetic thrust of the motor and reducing the unfavorable electromagnetic torque,the effects of different spatial relative position relationships between the armature coil and superconducting coil on the electromagnetic force and electromagnetic torque of the motor are investigated.Finally,based on the determined spatial relativity of the armature coil and the superconducting coil,the characteristics of eddy current loss distribution of armature winding are analyzed,the analytical model of eddy current loss of armature coil composed of circular or rectangular wire in 3D alternating magnetic field is established,and the model is verified by the experimental device developed,the analytical model of circulating current loss of armature winding is established,and the influence of different number of parallel windings on circulating current loss and electromagnetic thrust is analyzed by this model and verified by FEM.The research content of the armature winding AC loss provides the theoretical basis for the subsequent armature winding design.