| Permanent magnet synchronous motors(PMSM)have many advantages,such as small size,high efficiency,and notably wide high efficiency area,therefore they are widely used in daily life.Especially in the field of electric vehicles,PMSM is widely used in its driving structure.Due to the wide speed range of PMSM used in electric vehicles,resonance phenomenon is more likely to occur.When the electric vehicle is running,because of the existence of wind noise,tire noise and some other noises,low-frequency electromagnetic noise is likely to be cover,while the high-frequency electromagnetic noise is likely to be noticed.With consumers’ increasing demand for the comfort of electric vehicles,how to suppress the electromagnetic noise,especially to avoid amplification of electromagnetic noise due to resonance,is the urgent problems in the motor industry.Therefore,it is of great significance and practical value to study the electromagnetic noise of PMSM.In this paper,the electromagnetic noise of a PMSM of 48 slots and 8 poles for electric vehicles is studied as follows.Firstly,the electromagnetic noise theory of PMSM is studied.This part mainly includes the theoretical analysis of magnetomotive force,air gap permeability and electromagnetic force density of PMSM.The source of radial electromagnetic force and its spatial order and frequency characteristics of PMSM are analyzed,and the radial force wave table of 48 slot 8pole PMSM is obtained according to the analytical method.The modal analysis theory of PMSM is described.The source of noise,physical measurement and calculation theory of radiated noise are summarized.Secondly,the air gap flux density and electromagnetic force density of PMSM are simulated and analyzed.ANSYS Maxwell 2D finite element software is applied to establish the two-dimensional model of PMSM.The radial air gap flux density,tangential air gap flux density and radial electromagnetic force density of the motor in rated and no-load conditions are simulated and analyzed.The harmonic analysis of radial electromagnetic force density is carried out by using two-dimensional Fourier decomposition,and the spatial order and frequency characteristics of radial electromagnetic force density are obtained.It provides the basis for the analysis of electromagnetic noise of PMSM.Thirdly,the finite element software is used to establish the three-dimensional mechanical model of PMSM.ANSYS Workbench modal module is applied to analyze the modal parameters of the stator of PMSM.And the influences of winding structure and shell structure on the modal parameters of the stator are studied respectively.It is concluded that the additional of winding structure and shell structure will increase the natural frequency of stator.In the final,the modal parameters of the cover and stator system are analyzed.Finally,the multi speed harmonic response of PMSM is analyzed by using ANSYS Workbench,and the ERPL waterfall diagram under the rated condition and no-load condition is obtained.Combined with the simulation results of radial electromagnetic force density and modal parameters,it is concluded that the reason for the high-frequency 48 order noise problem of the motor is that the 12 times fundamental frequency component of the 0-order electromagnetic force wave resonates with the motor structure.Then the influence of the way of step skewing,width of stator rabbet and motor structure on 48 order noise is analyzed.For that PMSM,the 48 order noise can be effectively reduced by the bilateral step skewing compared with the non-step skewing.Two kinds of motor structures with damping plate added between stator and shell is analyzed,the simulation results show that both the structure can effectively suppress the radiation of high frequency noise on the shell surface,and the motor structure with the damping plate embedded in the shell has better suppression effect on high-frequency noise than the motor structure with the damping plate attached between the stator and the shell. |
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