Calculation And Analysis Of Electromagnetic Noise Of Permanent Magnet Synchronous Motor Applied In Electric Vehicle

Disc permanent magnet synchronous motor with axial magnetic field is often used as the driving motor of electric vehicles because of its advantages such as simple structure,high torque inertia ratio,compact structure,high efficiency and high power density.With the improvement of people’s life quality,higher ride comfort of electric vehicles has also been required.As the driving motor of electric vehicle,the vibration and noise of permanent magnet synchronous motor are important indexes to appraise its performance.At present,the electromagnetic noise of induction motor and radial magnetic synchronous motor is mainly analyzed,and the electromagnetic noise of disk permanent magnet synchronous motor is less studied.This paper mainly calculates and analyzes the electromagnetic noise of the disc permanent magnet synchronous motor used in electric vehicles.The main research contents are as follows:(1)The magnetic field of disc permanent magnet synchronous motor is analyzed.The equivalent magnetic network model of the disc permanent magnet motor is established.The equivalent reluctances in the model are calculated by the differential method.Then,the analytical expression of the magnetic flux leakage coefficient of the disc permanent magnet motor is obtained.The end effect correction function of air gap magnetic field is obtained by dichotomy optimization,which is suitable for different sizes,different pole slot composing and different structure types of axial magnetic disc permanent magnet motors.Then,the analytical model of open circuit air gap flux density is established at average radius taking the slot effect into consideration,and the analytical result is compared with the result of FEM.The harmonic analysis of the axial electromagnetic force density under no-load and load shows that the frequency of the axial electromagnetic force wave is equal to the integer multiple of the product of the fundamental frequency of the motor rotation and the number of poles.The numerical method is adopted to calculate the frequencies of axial electromagnetic force wave corresponding to different orders.It is concluded that the low harmonics of axial electromagnetic force are the main excitation source of electromagnetic noise.(2)The air gap flux density wave,no-load back electromotive force and torque ripple of the disc permanent magnet synchronous motor are optimized.The analytical expression of no-load back-EMF of the machine is obtained by establishing the equivalent magnetic network,and the analytical result is compared with the result of FEM.For sector permanent magnets,the sine distortion rate of air gap flux density and back-EMF wave can be reduced by using the arcshaped PM optimization method,and the torque ripple can also be suppressed.The smaller radius of arc shaping is,the smaller end of permanent magnet thickness is,the smaller sine distortion rate of air gap flux density is.The average torque of the motor can be improved by using the eccentric arc-shaped PM optimization method which is equivalent to the traditional optimization method of addicting third harmonic to the sine-shaped magnet.(3)The natural frequency of disc permanent magnet synchronous motor is analyzed.The axial modal of stator core with windings is simulated and analyzed.It is found that the stator core with windings will increase the axial modal frequencies.The axial mode of the combinations of the stator core,the end cover and the casing are simulated and analyzed.It is found that the casing with the end cover will increase the axial modal frequencies.As the thicknesses of the end cover and the casing increase,their axial modal frequencies increase.The modal frequencies of the whole machine are far away from the harmonic frequencies of the axial electromagnetic force wave,so the possibility of resonance of the motor is relatively small.(4)The electromagnetic noise of disc permanent magnet synchronous motor is analyzed.The electromagnetic noise of the motor is simulated and analyzed through multi-physical field coupling simulation.The electromagnetic noise is reduced by 2.5d B after optimization,which confirms the effectiveness of the above-mentioned electromagnetic noise optimization method.