Research On Analysis And Suppression Of Electromagnetic Force Ripple For Precision Permanent Magnet Linear Synchronous Motor

Compared with the traditional linear motion device composed of rotary motor and mechanical transmission parts,permanent magnet linear synchronous motor(PMLSM)is easier to obtain high thrust,high speed,high dynamic response,and high precision,so it has a wide application prospect in the field of precision linear motion.Due to the longitudinal breaking of the primary iron core,the PMLSM has a unique longitudinal end effect.On the one hand,the longitudinal end effect is coupled with the cogging effect,which leads to the large distortion of the air gap magnetic field.On the other hand,it leads to the discontinuous arrangement of the motor windings,resulting in the winding asymmetry effect.Due to the existence of end effect,cogging effect and winding asymmetry effect,the thrust and normal force of the PMLSM fluctuate to a certain extent,which limits the further application of the motor in the field of ultra/high precision motion.In this paper,the PMLSM used in the field of precision motion is taken as the research object.For the motor,the mechanism of cogging effect,end effect,incremental magnetic field effect,and winding asymmetry effect on the electromagnetic force ripple is studied.The primary component segmented design scheme is put forward systematically,so as to suppress the electromagnetic force ripple components of the motor,and finally realize the low electromagnetic force ripple operation of the motor.For the PMLSM,the mechanism of thrust ripple is firstly studied.According to different influencing factors,the mechanism of the cogging effect,the end effect,the incremental magnetic field effect and the winding asymmetry effect on the thrust ripple of motor is analyzed.The analytical expression of cogging force is constructed,then the quantitative relationship between the periodic characteristics of cogging force and the motor pole slot fit is obtained.The master-slave and the vector magnetic potential boundary models are established for comparative analysis.The influence of the end effect on the air gap magnetic field in the end region and the coupling region is obtained respectively,and then the analytical expressions of the single end force and the pulsating force are constructed.The influence of winding asymmetry effect on the motor thrust ripple characteristics is analyzed by establishing the calculation model.The results show that the winding asymmetry effect leads to the thrust fluctuation component which is positively related to the armature current.Secondly,the mechanism of the normal force ripple of the PMLSM was studied,and the mechanism of the cogging effect,the end effect and the armature reaction on the motor normal force ripple was analyzed and revealed.The normal force model of the motor under the influence of cogging effect is constructed based on the superposition principle.Based on the Schwarz-Christoffel transform,the influence of end effect on the normal component of air gap magnetic density is analyzed,of which the results show that the end effect will affect the normal force of both end and non end core teeth.The calculation model of normal force component affected by armature reaction is established,and then the influence law of armature reaction on normal force ripple is summarized.In order to suppress the electromagnetic force ripple of the PMLSM,the design scheme of PMLSM with segmental primary component was proposed,and the principle of suppressing the thrust ripple and normal force ripple was studied and revealed respectively.Firstly,the principle of restraining the detent and thrust fluctuation of the motor with segmental primary component is described by establishing the detent force model and winding terminal voltage model.On this basis,the combination scheme of fractional pole and primary segmented type is further proposed,which can effectively suppress the third and its multiple harmonics in the unit motor thrust ripple,and then the whole motor thrust ripple can be finally suppressed to a very low level.In the aspect of normal force ripple,which is regarded as the resultant force,the principle of restraining normal force ripple is expounded by establishing the normal force ripple model for the motor with segmental primary component.In addition,the normal force of the motor is regarded as a component force acting on the surface of each primary core tooth.Coupling the electromagnetic field and the stress field,the influence of the normal force ripple on the motor primary deformation is analyzed.It is pointed out that the primary segmented scheme has the defect of increasing the primary deformation of the motor.The coupling effect between of the PMLSM with segmental primary component is studied.The Schwarz-Christoffel transform is used to establish the static modeling,and the influence of the coupling effect on the magnetic field at the end of the primary iron core is obtained.The ripple models of the detent force and the normal force considering the coupling effect are established respectively,so as to grasp the influence law of the coupling effect on the the thrust ripple and the normal force ripple of the motor.On this basis,the design criterion of the PMLSM with segmental primary component considering coupling effect is proposed,and it is pointed out that the equivalent flux barrier width should be greater than 3 times the equivalent air gap.Finally,the PMLSM test platform with linear guide supporting structure is built to test the detent force,static thrust,normal force and back EMF of the prototype.Several prototypes,including the motor with whole primary component and segmental primary component,are manufactured and tested to further verify the correctness and effectiveness of the theoretical analysis in this paper.