Multi-physics Coupling Analysis And Optimization Of A High-speed Permanent Magnet Motor

With the advantages of high speed,high power density,small size and high efficiency,high-speed permanent magnet motor has been widely used in industrial intelligent manufacturing,modern transportation,aerospace,national defense equipment and other fields.Motor design should primarily meet the basic electromagnetic performance index,but high-speed permanent magnet motor also need to controlled mechanical strength,temperature rise and other aspects.In order to meet the comprehensive performance requirements of high-speed permanent magnet motor,this paper will make a comprehensive analysis of the motor from the perspective of multi-physical field coupling,which is of great engineering significance.Taking a high-speed permanent magnet brushless DC motor as the research object,the motor is used to equip the steering gear system and provide power for the steering gear.Due to the particularity of the working conditions of the motor,it needs high comprehensive performance.Therefore,this paper focuses on the electromagnetic,temperature rise and strength of the motor in the way of sequential coupling of electromagnetic field,temperature field and mechanical stress field.In view of the structure characteristics and requirements of high-speed permanent magnet motor,the theoretical calculation of electromagnetic field,temperature field and stress field existing in the motor is mainly carried out.The coupling phenomena and interrelations of physical fields in the motor are analyzed.The solution strategy is studied.Combining with the performance index of the equipment motor,the analysis,which lays a foundation for the later multi-physical field coupling analysis,is carried out from the aspects of stator,rotor and permanent magnet.The high-speed permanent magnet motor circuit is coupled with the magnetic field to obtain the magnetic field and output torque performance characteristics of the motor.Inorder to solve the problem of large fluctuation of motor torque,the structure parameters of stator and rotor are taken as variable factors,and the influence of variable factors on cogging torque is analyzed.The parameters of variable factors are optimized by multi-variable response surface optimization method,and the optimization factors are simulated by finite element method to verify the effectiveness of the optimization scheme.The phenomenon of heat exchange in high-speed permanent magnet motor is analyzed.The heat dissipation coefficient of each part in the process of heat exchange is determined.The electromagnetic loss is loaded into the temperature field of the motor and the finite element model of magneto-thermal coupling temperature rise is established.The temperature rise distribution of the stator,rotor and the whole machine is analyzed in detail.Comparing the change trend of motor temperature rise under different load conditions,the analysis lays a foundation for structure optimization.According to elastic-plastic mechanics,the analytical formula of rotor strength should consider assembly prestress,temperature-rise stress and centrifugal force.The influencing factors of rotor strength are analyzed.The temperature field of rotor obtained by magneto-thermal coupling is loaded into the mechanical structure field of rotor,and the numerical analysis model of thermal-mechanical coupling is established.The stress distribution law of sheath and permanent magnet under three operating conditions is mainly analyzed to determine whether the motor can run normally at high temperature and high speed or not.The influence trend of different interference,temperature and sheath thickness on rotor strength is studied,which provides a basis for motor rotor design and optimization.Through multi-physical field coupling analysis and optimization,the structure parameters of the motor are obtained to the motor prototype.the motor test platform is built,and the experimental method of performance testing is established to obtain the experimental data are obtained.The numerical results are compared to verify the effectiveness of the coupling simulation analysis method.