Modelling And Experimental Investigation Of 3D Electromagnetic Forces Of Ironless Double-layer-winding Superconducting Linear Synchronous Motor

Electrodynamic suspension(EDS)train has realized the speed of 603 km/h in the manned operation test,which makes the EDS system a promising candidate for the high-speed railway of the next-generation.Linear motor is a key part of the EDS system that it propels the EDS train without the mechanical contact.Due to the high magnetic field generated by the superconducting magnets,the ironless double-layer-winding superconducting linear synchronous motor(SLSM)shows the advantages of large gap,high efficiency,high thrust,and low thrust ripple.However,the application is limited by the analytical model with high accuracy,the complex working condition and the difficult experiments.Considering the special structure and working condition,the modeling,optimization design,characteristic analysis and experiments of ironless double-layer-winding SLSM are processed in the following order.Firstly,an analytical model is proposed to calculate the no-load magnetic field,back electromotive force and the electromagnetic forces of ironless double-layer-winding SLSM.Considering the exciting current flowing on the centerline of racetrack superconducting coil,the no-load magnetic field is calculated based on the Biot-Savart law.Then,the mutual inductance between the racetrack exciting coil and the racetrack primary coil is computed upon the flux linked by the racetrack primary coil and the inductance matrix of SLSM is further deduced.Finally,the electromagnetic forces of ironless double-layer-winding SLSM is derived based on the virtual work method.In addition,the back electromotive force of ironless double-layer-winding SLSM is derived based on the Faraday’s law of electromagnetic induction.The variable postures of the secondary are introduced into the model using the three-dimensional coordinate transformation of the central point of the exciting coil.Furthermore,the number and distribution of the primary coils and the exciting coils are taken into consideration.Secondly,the optimal design of SLSM is carried out based on the geometric parameters of the racetrack superconducting magnet and the racetrack primary coils.The effects of the racetrack superconducting magnet and the double-layer winding on suppressing harmonics of magnetic fields are analyzed to improve the structure of SLSM.The influence of superconducting magnet on the thrust is discussed.In detail,the effects of the conductor cross-section and the pole-arc coefficient are analyzed.Then,taking the double-layer structure of the primary into account,the influences of the width,coil pitch and turns of the primary coils on the thrust are discussed.Finally,the conductor cross-section of superconducting magnet,the pole-arc coefficient of superconducting magnet,the width,coil pitch and turns of the primary coils are optimized to improve the thrust and thrust density and suppress the ripple.Based on the works above,a design method is proposed to optimize the superconducting magnet and primary coils of ironless double-layer-winding SLSM.Thirdly,the traveling magnetic field generated by the double-layer winding is analyzed in term of the distribution and the magnitude.The results indicate that the effect of traveling magnetic field on the critical current is so weak that it could be neglected in the J_c(B)relationship considering the anisotropy of superconducting tape.Then,the winding factor of racetrack coil is deduced and adopted to prove the effect of arc edges on suppressing the harmonics of back electromotive force.Furthermore,the back electromotive force coefficient of SLSM is also calculated.Next,the dependences of the thrust on the primary current and the variable postures of the secondary are studied.Finally,the primary current and the variable postures of the secondary are taken as the variables to analysis their effects on the normal force and the lateral force,respectively.It is shown that the existence of the normal force is depended on the initial phase angle of the primary current and the rotational motion of the secondary magnets around y axis,respectively.Similarly,the existence of the lateral force is depended on the co-effect of the initial phase angle of the primary current and the lateral motion of the secondary magnets.Finally,the prototype of ironless double-layer-winding SLSM is fabricated and tested on a self-made platform.The force-position curves are measured to investigate the influences of the variable postures of the secondary on the electromagnetic forces of SLSM.Then,the steady-state forces are measured by static equivalent experiments simulating the synchronous operation state of SLSM.That is,the secondary is adjusted by a three-dimensional location device to simulate its variable postures,and the three-phase AC current of the primary is simulated with three DC current sources.Based on the static equivalent experiments,the no-load magnetic field and the steady-state forces are investigated and the three-dimensional analytical model of ironless double-layer-winding SLSM is verified by the test results.