Research On Air-gap Deformation And Vibration Characteristics Of Interior Permanent Magnet Synchronous In-wheel Motor

Given its unique advantages,the distributed drive system has become one of the key technologies for the next generation electric vehicles.As its main power component,the in-wheel motor is faced with large and complicated problems in electromagnetic performance,mechanical structure,cooling and heat dissipation,vibration and noise reduction.Therefore,as one of the key problems,analysis and reduction of the in-wheel motor vibration is of great significance to the development of electric vehicles.Combined with the operating conditions and the installation environment of the in-wheel motor,the mechanical structure problem in the high performance permanent magnet synchronous in-wheel motor(PMSIWM)is more prominent,so that the impacts of electromagnetic excitations in the motor are more complicated.In addition,the vibration analysis of in-wheel motor should consider the coupling relationship of multiple physical fields.It is more difficult to establish the model of stator system.Aiming at these problems,this thesis focuses on the vibration characteristics of the IPMSIWM under limited conditions.The main research work includes the following aspects:Firstly,in order to solve the rotor mechanical strength problem in the IPMSIWM at high-speed condition,an equivalent analytical model is proposed to calculate the mechanical stress of the interior rotor,which could guide the design of rotor structure in the IPMSM.Based on the simulation analysis of the structural field,the effects of rotor structure parameters on mechanical strength are compared and analyzed.Then the distribution laws of the stator elliptical deformation and the pole shoe centrifugal distortion are investigated.And the influences of rotor structural parameters on the distribution curves of rotor deformation are analyzed.Combined with the rotor fault analysis and mechanical strength experiments of the in-wheel motor prototype,the optimizations of interior rotor structure for suppressing the pole shoe deformation are proposed.Secondly,based on the traditional electro-mechanical analogy method,the circumferential natural frequency of the stator system is quickly calculated,which can be used to qualitatively analyze the influence of structural parameters on the modal frequency of the system.According to the structural analysis of stator core,winding and frame of the high torque density in-wheel motor,the equivalent material physical properties of each component in the stator system and the contact conditions between each component are analyzed.In addition,the prototype of the motor is fabricated;then the experimental modal analysis of the stator system and its subassemblies are carried out during the manufacturing process.Through comparisons of the results between experiments and FEA,the final model of the stator system is determined and verified to be of high accuracy to predict the vibration behaviors of the IPMSM with concentrated winding.And several factors influencing the modal frequencies of stator system are analyzed based on this accurate model.Afterwards,for the air-gap shape change caused by the stator and rotor deformation in IPMSIWM,the air-gap magnetic flux field under air-gap deformations is analyzed based on the air-gap conductance method.Combined with the Maxwell Stress Tensor Method,the mathematical expression of radial magnetic force density considering air-gap deformations is derived.By establishing the electromagnetic finite element models of investigated IPMSMs under different air-gap states,the distributions and harmonics of air-gap magnetic flux density are analyzed.Therefore,the magnetic force densities considering air-gap deformations at different conditions are analyzed.Then the two-dimensional Fourier analysis is used to study the changing laws of its temporal and spatial harmonics.In addition,the effects of air-gap deformations on the waveforms and harmonics of electromagnetic torque are analyzed.The change rules of harmonic torque characteristics are studied based on MSTM.Lastly,based on the accurate structural model of the stator system,the vibration characteristics of the IPMSIWM are investigated with loading different electromagnetic excitations on the stator inner face.All the structural simulations are carried out based on the analysis module Harmonic Response of the software ANSYS.Then,the motor vibration characteristics under the radial magnetic force,the tangential magnetic force and the torque ripple are analyzed and compared.And the influences of different air-gap deformations on the vibration characteristics at different limited conditions are investigated.Through the comparison between experimental results and FEA results,the method of accurate predicting the motor vibration characteristics is determined,which provides a reference for the vibration optimization and reliability design of the in-wheel motor.