Study On The Force-magnetism Properties Of The HTS Bulk Magnet Subjected To Traveling Magnetic Field

As the preparation technology of superconducting materials matures,the application of high-temperature superconductivity technology develops rapidly.Due to its excellent trapping flux ability,HTS bulk materials can be used as quasi-permanent magnets instead of conventional permanent magnets in linear motors.High-temperature superconducting linear motors have the advantages of light weight,small volume,and high work efficiency.The main research work on HTS linear motor begins at the end of the last century.Although many progressive achievements have been achieved,its developments obviously lag behind the superconducting rotating motor in both experimental and theoretical researches.It means studies on HTS linear motor are still at an early stage of practical application.Meanwhile,the trapped magnetic fluxes of high-temperature superconducting bulk magnets will gradually attenuate or even disappear in the traveling wave magnetic field generated by the stator of the linear motor,thereby greatly affecting the propulsive force and levitation force,the motor performance.Combined with the current research background,the relevant experiments and simulations of the electromagnetic force,trapped magnetic flux,and AC loss of hightemperature superconducting bulk magnets in a traveling-wave magnetic field are performed.This aims of the thesis is to explore the application characteristics of high-temperature superconductor bulk materials in linear motors.The main works include building multiphysics test platform and collecting force and magnetic field at the same time.Through multiphysics test platform experiments,the effects of different magnetization currents on the electromagnetic force and trapped magnetic flux of high-temperature superconductor bulk material in traveling wave magnetic field are investigated.When the amplitude and frequency of the primary three-phase alternating current of the linear motor are changed,the variation of electromagnetic force and the trapped magnetic flux inside the bulk are investigated.It is found that the electromagnetic force will appear phase shift when the magnetizing current is small.The larger the frequency,the greater the attenuation of the trapped magnetic flux has,due to inductive current redistribution and the temperature rise caused by the AC loss.After clarifying the reason of the attenuation of the trapped magnetic flux in the traveling wave magnetic field,several effective measures are proposed to suppress the attenuation.By the combination method of experiments and simulations,the influence of the ferromagnetic sheet and the copper ring on the magnetic trapped attenuation and electromagnetic force of high-temperature superconducting bulk material is investigated.As a result,it is found that the addition of a ferromagnetic sheet above and below the bulk can suppress the attenuation of the trapping magnetic flux density of the high temperature superconductor bulk material.Meanwhile it also causes a distortion of the electromagnetic force,due to the inductive electromagnetic force caused by the ferromagnetic sheet.The addition of copper rings to the bulk has no inhibitory effect on the attenuation of the trapping magnetic flux density of the high temperature superconductor bulk in the power frequency range of the linear motor.A two-dimensional model of high-temperature superconducting bulk in traveling wave magnetic field is established.The simulation steps of the model are described in detail.The influence of the quantity and height of the HTS bulk on the electromagnetic force was further studied.The influence of large travelling magnetic field on the magnetic flux of the high temperature superconductor bulk magnet was analyzed through the internal induced current density redistribution.Finally,the AC losses distribution of HTS bulk caused by standing wave and traveling magnetic field were compared.It was found that the increase of the number of HTS bulks did not result in additional electromagnetic force increments.The increase of bulk's height could lead to the increase of the electromagnetic force at the lower range.The thrust reaches a certain saturation value with increasing of height.Due to the reduction of the magnetic field in the air gap,continuing to increase the height would not lead to the electromagnetic force substantial increase.When the strength of the traveling wave continuously increased,the density of the trapped magnetic flux in the HTS bulk decayed first and then raised,which could be explained by the remagnetization of the HTS bulk.The AC loss in HTS bulk subjected the standing wave field is greater than AC loss caused by traveling magnetic field.The distribution of the AC loss in the traveling wave magnetic field is related to the direction of the traveling wave magnetic field.