Research On Demagnetization Of Permanent Magnet Of Interior Permanent Magnet Synchronous Motor

Interior permanent magnet synchronous motor,which has the advantages of wide speed regulation performance,high power density,small size,is widely used in the electric vehicle drive.Compared with other types of motors,permanent magnet motor has some unsurpassed advantages,but there are also some disadvantages.As a type of permanent magnet motor,interior permanent magnet synchronous motor has problems of large permanent magnet magnetic field fluctuation and permanent magnet demagnetization.At present,the irreversible demagnetization of permanent magnet is the most serious problem faced by permanent magnet motor.Once the permanent magnets are irreversibly demagnetized,the performance of the motor will decrease and even the entire drive system will be damaged.This thesis takes a 48-slot,8-pole,50 k W interior permanent magnet synchronous motor as the research object.The research is carried out from the basic parameter calculation of the motor,the establishment of different demagnetization fault models of permanent magnet,the electromagnetic field analysis of the permanent magnet motor under different demagnetization current and the temperature field analysis and other aspects.The main research contents are as follows:(1)Based on the magnetic properties of permanent magnet materials,the reasons for irreversible demagnetization of permanent magnets are analyzed.Combined with the reasons of demagnetization,the process and law of irreversible demagnetization of permanent magnets are studied.(2)With the help of Maxwell finite element simulation software,a twodimensional simulation model of the interior permanent magnet synchronous motor is built in the steady-state and transient fields.The basic parameters of the motor were calculated and analyzed,and the torque performance of the motor was analyzed.(3)The demagnetization curves of permanent magnet materials at different temperatures are analyzed,and the operating points of permanent magnets under various working conditions are calculated.According to the relationship between the working point of the permanent magnet and the inflection point of the permanent magnet demagnetization curve,whether the permanent magnet will be irreversibly demagnetized is evaluated.By constructing the permanent magnet overall uniform demagnetization model and the permanent magnet local demagnetization model,the changes of the motor performance parameters no-load back EMF,no-load flux linkage,and air gap flux density under demagnetization are analyzed.The harmonic content of no-load back EMF and air gap magnetic density under different degrees of demagnetization of permanent magnets is analyzed,and the law of irreversible demagnetization of permanent magnets is preliminarily obtained.(4)By applying different magnitudes of direct-axis reverse current as the demagnetization current excitation,the demagnetization of permanent magnets under different magnitudes of demagnetization current is analyzed.By analyzing the relationship between the minimum working magnetic density of the permanent magnet and the no-load back electromotive force,the law of irreversible demagnetization of the permanent magnet and the actual judgment basis are obtained.(5)The loss of the motor at no-load,rated load and different demagnetization currents is calculated;the volume,thermal conductivity,heat generation rate,etc.of each part of the motor are calculated;Taking the loss of each part of the motor as the heat source,with the help of ANSYS Workbench simulation tools,the internal temperature field distribution of the motor under no-load,rated load and different demagnetization currents is analyzed.