Diagnosis Of Air Gap Eccentricity For Interior Permanent Magnet Synchronous Motor Based On Stray Flux Signal

Owing to the advantages of high torque density,good flux-weakening capability and high efficiency,the interior permanent magnet synchronous motor(IPMSM)is widely used as the traction motor for electric vehicles.In order to reduce the no-load flux leakage coefficient,improve the motor performance and save the consumption of permanent magnet,however,the air gap length of IPMSM for electric vehicles is generally small,and it is more sensitive to the air gap eccentricity.The air gap eccentricity aggravates the vibration and noise of the motor,and even induces the contact fault between the stator and rotor,which may scrap the motor.Therefore,the research on air gap eccentricity diagnosis for IPMSM has important theoretical significance and engineering value.The main research work and achievements are as follows:(1)Modeling and analysis of air gap eccentric stray magnetic field of IPMSM.Firstly,based on the Equivalent Magnetic Circuit(EMC)analytical model of the non-eccentric open circuit air gap radial magnetic flux density,an analytical model of radial magnetic flux density of eccentric stray magnetic field is established by using eccentric permeability correction coefficient and generalized stray magnetic field attenuation coefficient,and the influence of air gap eccentricity on the time-frequency characteristics of radial magnetic flux density of stray magnetic field is revealed.Then,the air gap magnetic field,stray magnetic field and detection coil voltage are calculated by using the electromagnetic Finite Element Model(FEM).The accuracy of the analytical model is verified,and the eccentricity sensitivity of different signals is analyzed.The results show that:in all signals,the amplitude of the fundamental wave(frequency f_c)near the static eccentricity angle is positively correlated with the static eccentricity,while the amplitude of the fundamental wave far away from the static eccentricity angle is negatively correlated with the static eccentricity,and there is no obvious relationship between the amplitude of the fundamental wave and the dynamic eccentricity;The average value of sideband harmonics(frequency f_c±f_r)amplitude is positively correlated with dynamic eccentricity,but not with static eccentricity;The difference of eccentricity sensitivity of each signal is less than one time,which means that these signals is capable of being applied to the diagnosis of air gap eccentricity(f_c=pf_r,f_r is the rotational frequency of the motor,p is the number of pole pairs of the motor).(2)Reserch of experimental study on air gap eccentricity of IPMSM and eccentricity prototype.A prototype with quantitative adjustment of air gap eccentricity is designed and manufactured.The static and dynamic eccentricity and eccentricity direction of the prototype are adjusted by screw mechanism,double eccentric sleeves group and rotatable end cover,respectively.The stray magnetic field radial flux density and search coil voltage of the prototype under different eccentricities were collected.Through FFT,the spectrum characteristics of the signals are analyzed.The results show that the eccentric prototype can accurately simulate all kinds of mixed eccentricity;The experimental results verify the accuracy of the analytical model and the FEM.(3)Air gap eccentricity diagnosis of IPMSM based on BP neural network.Two kinds of BP neural network diagnosis models for air gap eccentricity are established by using the experimental data.One diagnostic model adopts the radial flux density of stray magnetic field as the diagnostic signal,while the other one adopts the search coil voltage.The results show that the average error of static and dynamic eccentricity of these two diagnostic models is less than 0.015,and the average error of eccentric circle angle is less than 18°;The two diagnostic models reach a similar diagnostic accuracy.