Study On Demagnetization Mechanism And Local Infiltration Of Heavy Rare Earth For PMSM Used In New Energy Vehicles

Permanent magnet synchronous motor(PMSM)for new energy vehicles(NEV)has a series of advantages such as small size,strong overload capacity and high-power density,but the magnet of the motor is vulnerable to the influence of electromagnetic and thermal irreversible demagnetization phenomenon.By adding a large amount of rare earth elements such as dysprosium and terbium in the preparation of magnet,the motor magnet can have higher demagnetization resistance.However,the cost of the motor is greatly increased by this method.Using local infiltration of heavy rare earth for magnet is a better choice to improve the demagnetization resistance of the motor.In this dissertation,a triangle-pole structure PMSM is taken as the research object,the demagnetization characteristics of magnet are analyzed,and the local infiltration of heavy rare earth scheme is designed and optimized.Considering the scheme of heavy rare earth infiltration,it is necessary to determine the demagnetization position,fault evolution rule and demagnetization degree of magnet,so it is also important to study the demagnetization characteristics of PMSM for NEV.This dissertation designed a PMSM for NEV,established a two-dimensional simulation model of the motor,and defined the critical demagnetization temperature of magnet at peak working conditions.Meanwhile,this dissertation analyzed the influence of three demagnetization factors,temperature,armature current amplitude and flux-weakening angle,on the demagnetization characteristics of magnet.The demagnetization position and fault evolution rule of interior PMSM are obtained,and the electromagnetic performance of the motor after demagnetization is studied.Aiming to satisfy the low heavy rare earth consumption and strong demagnetization resistance of magnet,the motor magnet is replaced from N38 UH with N38 SH containing relatively less heavy rare earth elements on the premise of not reducing the performance of the motor at peak working conditions,and the inherent coercivity of magnet in the demagnetization part is improved by proposing a reasonable selection design of heavy rare earth infiltration.The demagnetization resistance of the motor is improved,and the two key design parameters in the scheme,namely the increase ratio of intrinsic coercivity and the depth of heavy rare earth infiltration,can be determined by the demagnetization degree of the magnet.To improve the accuracy and reliability of the selection heavy rare earth infiltration scheme,this dissertation combines the intrinsic demagnetization curve principle of magnet with the maximum demagnetization rate,and puts forward a method suitable for calculating the maximum intrinsic coercivity increase multiple in the design scheme of selection heavy rare earth infiltration,which can be used to optimize the design scheme of selection heavy rare earth infiltration,and compares the schemes before and after optimization.It is found that the optimized scheme not only meets the electromagnetic performance requirements of PMSM for NEV,but also further reduces the consumption of heavy rare earth elements,and achieves the fine design of the scheme of selective heavy rare earth infiltration of magnet for the motor.