Study On Analysis And Reduction Solutions Of Shaft Voltage In Interior Permanent Magnet Synchronous Motors

The inherent shaft voltage is induced in the shaft owing to unbalanced magnetic field caused by the pole and slot combinations in permanent magnet synchronous motors.For interior permanent magnet synchronous motors(IPMSMs)driven by inverters,most studies focus on the effect of common mode voltage on bearing voltage.The inherent shaft voltage is usually ignored.However,when the inherent shaft voltage exceeds the threshold voltage of bearing lubricant,the bearing current is generated.The bearing will be damaged in a short time.Eventually,the reliability of IPMSMs is reduced.Therefore,the analysis and reduction solutions of shaft voltage are of great significance to improve the reliability and stability of IPMSMs.This paper analyzes the shaft voltage of IPMSMs with and without squirrel cage winding.Then,the reduction methods of shaft voltage are studied.The main tasks are listed as follows:1.Analysis of the Inherent Shaft Voltage.The expresssion of the inherent shaft voltage under no-load condition is derived by analytical method.The existence criterion and characteristic frequency of the inherent shaft voltage are summarized.The effect of pole and slot combinations,rotor speed and armature core length on the inherent shaft voltage are investigated.Then,the models of the inherent shaft voltage under no-load condition are established by using Maxwell 2D finite element software.Next,the simulation results obtained by finite element method(FEM)verify the accuracy of analytical analysis.2.Research on Reduction Methods of the Inherent Shaft Voltage.In the view of the design of electromagnetic structure,mitigation techniques of the inherent shaft voltage are studied.For IPMSMs with squirrel cage winding,this paper mainly investigates mitigation techniques such as rotor teeth width design,rotor teeth pairing design,rotor slot pairing design and skewed stator slots design.The effectiveness of the above measures is verified by FEM.As for IPMSMs without squirrel cage winding,the reduction solutions based on the selection of pole-arc coefficient,the combination of pole-arc coefficient pairing are studied.Then,the methods based on uneven air gap structures and skewed stator slots design are studied.Finally,the effectiveness of the above solutions is verified by FEM.3.Analysis of Shaft Voltage under Eccentricity Fault.By means of correction coefficient of air-gap permeance method,the expression of shaft voltage under eccentricity fault is derived.Then,the characteristic frequency of shaft voltage under static,dynamic and mixed eccentricity fault are obtained,respectively.It is found that the characteristic frequency under mixed eccentricity fault not only includes the characteristic frequency of shaft voltage under static and dynamic eccentricity fault,but also increases by v/p(v=1,2...),(kNd±v)/p(k=1,2...,v=1,2...)times the synchronous speed frequency.The influence of the eccentric angle of the initial position on the eccentric shaft voltage is analyzed by FEM.The models of eccentric shaft voltage with different pole and slot combinations are established.Shaft voltage at different eccentric degree is calculated by FEM.The characteristic frequency content of shaft voltage is consistent with analytical analysis under static,dynamic and mixed eccentricity fault.4.Study on the Reduction Methods of the Eccentric Shaft Voltage.The components of the eccentric shaft voltage are investigated under static,dynamic and mixed eccentricity fault,respectively.The Fourier coefficients of air gap magnetic conductivity,magnetomotive force and magnetic conductivity’s correction coefficient are analyzed which correspond to the shaft voltage component of a certain characteristic frequency.The reduction method of eccentric shaft voltage based on the selection of pole-arc coefficient is studied.Besides,the method to reduce eccentric shaft voltage by combining the pole-arc coefficient with non-uniform air gap structure is investigated.The effectiveness of reduction solutions under static,dynamic and mixed eccentricity fault is verified by FEM,respectively.