Research On Demagnetization Mechanism Of Permanent Magnet And Anti-Local Demagnetization Optimization On The Permanent Magnet Synchronous Machine

The permanent magnet synchronous motor is favored as the preferred solution for electric vehicle propulsion due to its high efficiency,high power density,high torque density,and wide speed range.However,the permanent magnets are temperature sensitive and may experience local irreversible demagnetization under certain operating conditions,which can significantly impact the motor’s output performance.Therefore,conducting research on demagnetization of the permanent magnet synchronous motor and optimizing it to be more resistant to demagnetization is of great significance.The demagnetization problem of permanent magnet synchronous motor is studied by an 8-pole 48-slot built-in permanent magnet synchronous motor,and the demagnetization analysis of the permanent magnet motor is carried out in terms of both temperature and reverse magnetic field.First,according to the motor index,through the study of the main dimensional structure,the size of the air gap,the thickness and width of the permanent magnet and other design factors,the finite element simulation software is used to establish a twodimensional model of the permanent magnet motor,and the no-load simulation,load simulation and the stress on the rotor during high-speed operation are calibrated to verify the reasonableness of the motor and lay the foundation for demagnetization analysis and optimization in the later paper.Secondly,the demagnetization mechanism of permanent magnets is discussed,and the demagnetization of permanent magnets under two typical demagnetization causes of high temperature and high current is studied in depth,and the relationship between demagnetization domain and demagnetization rate and demagnetization factors is summarized by introducing the demagnetization "monitoring line",and the conclusion that demagnetization occurs first in the local position of permanent magnets.Based on this conclusion and calculations of the demagnetization domain,the critical demagnetization operating point of permanent magnets,the preliminary law of demagnetization,irreversible demagnetization,and the effect of different degrees of demagnetization on the motor are derived to provide directions for antidemagnetization optimization.Finally,according to the law and phenomenon of demagnetization of the motor,the rotor structure of the motor is optimized against local demagnetization.Four optimization methods are proposed,including optimizing the permanent magnet slot and rotor auxiliary slot,adding middle magnetic separation slot,adding bypass magnetic circuit and adding magnetic isolation slot on the surface of permanent magnet.Then these four motor models are subjected to performance checks and demagnetization analysis to verify the rationality of the motors and the improvement of the resistance to local demagnetization.Finally,considering the different concerns and weights of electromagnetic performance and anti-demagnetization ability of motors in different applications,the comprehensive performance and anti-local demagnetization ability of all schemes are integrated and compared,and the most reasonable optimization scheme is derived to provide reference and direction for the future continuation of research on antidemagnetization of permanent magnet synchronous motor permanent magnets.