Analysis Of The Eddy Current Losses Of Permanent Magnets In Permanent Magnet Synchronous Motors For Electric Vehicles Under Weak Magnetic Conditions

The Integrated Starter and Generator(ISG)system is a common driving method for hybrid vehicles,it requires good external characteristics,high efficiency and high power density for the motor.While the interior permanent magnet synchronous motor(PMSM)is widely used in ISG systems because of its high power density,good field weakening performance,high reliability and low noise,and its flexible shape and size.However,the rotor permanent magnet(PM)of permanent magnet synchronous motor of ISG has the risk of high eddy current loss,due to the system’s demand for weak magnetic expansion,the magnetic field distribution of the motor’s interior is more complicated,the effect on the eddy current loss of the permanent magnet will further aggravate the possibility of permanent magnet demagnetization and ultimately affect the performance of the motor.Therefore,this paper mainly studies the eddy current loss of the permanent magnet of the ISG permanent magnet synchronous motor under weak magnetic conditions.Firstly,this paper introduces the basic structure of ISG permanent magnet synchronous motor,and the basic characteristics of stator and rotor structure,the stator structure is identical with the pole slot of 12 poles/18 slots,the rotor adopts "one" and "V" pole structures respectively,in order to ensure the comparability of the two pole structures in the case where the total amount of permanent magnets is the same,the circumferential direction of "one" rotor permanent magnet is evenly divided into two parts.Based on the electromagnetic simulation software,a two-dimensional finite element simulation model is established to simulate the two kinds of rotor structures under no-load and load conditions,and the fourier decomposition is used to analyze the harmonic content of the magnetic field under the no-load of the motor.Then the generation mechanism and influencing factors of eddy current loss of permanent magnet are studied,the effects of tooth harmonics,time harmonics and space harmonics on eddy current loss of permanent magnet of rotor are investigated,the effects of slot width on eddy current of permanent magnet and eddy current loss influencing factors under different slot matching are calculated,the eddy current situation of permanent magnet of rotor with two pole structures under Id=0 control mode and the trend of speed are explored.Finally,the principle of flux weakening for PMSM is explored,and the characteristics of its weak magnetic field under different operational trajectories are analyzed,the calculation methods of the inductance parameters of the PMSM are studied,the eddy current loss of the permanent magnets with different weak magnetic angles,different demagnetization currents and different rotational speeds,and the distribution characteristics of the magnetic field lines and the magnetic dense cloud maps under the same weak magnetic conditions are analyzed,and the permanent magnet surface is calculated,the magnetic flux and its change verify the law of the amount of eddy current loss of the permanent magnet.Finally,a prototype is made and a test platform is built to test the "one" permanent magnet synchronous motor with magnetic pole structure,according to the relationship between no-load back EMF,eddy current loss and temperature rise,the eddy current loss of permanent magnet is measured indirectly by back EMF measurement method,which is in agreement with the simulation results,and the rationality of the analysis is verified.