Research Of Rotor Structure Of PMA-SynRM For Electric Vehicle Application

Although most of the driving motors of new energy vehicles use rare earth permanent magnet synchronous motors,the price of neodymium iron boron rare earth permanent magnet materials is high,and the rare earth materials are non renewable resources.At the same time,under the condition of high temperature and the armature reaction of the weak magnetic control,the motor is prone to the loss of excitation fault,which leads to the failure of the control system and safety problems.However,the traditional reluctance motor has low efficiency,power factor and power density,so it is difficult to use it as the driving motor of new energy vehicles.Permanent magnet assisted synchronous reluctance motor(PMA-SynRM)combines the characteristics of permanent magnet synchronous motor and reluctance motor.It not only has the characteristics of high power density and torque,but also has the advantages of wide speed range and high cost performance.But the rotor topology of PMA-SynRM is relative to the internal permanent magnet synchronous motor,IPMSM)is more complex and has a great influence on the electromagnetic performance of the motor,such as torque,torque ripple,demagnetization ability and anti demagnetization ability.Therefore,how to design and optimize the rotor structure of the motor reasonably according to the characteristics of the motor is an important topic in the research of PMA-SynRM.Firstly,this paper summarizes the domestic and foreign literature related to PMA-SynRM for electric vehicle drive,including the development history and research status of PMA-SynRM,the research status of electric vehicle drive motor.Because PMA-SynRM makes full use of the characteristics of magnetoresistance,the ratio of permanent magnet torque in the electromagnetic torque is taken as the analysis standard of motor performance in this paper.Considering the complexity of rotor structure in motor design,based on the idea of combination of field and circuit,this paper takes the geometric dimension of rotor magnetic barrier as the design parameter,and adopts the method of combination of analytical calculation and finite element simulation analysis to optimize the rotor topology.Furthermore,the expression of the electromagnetic torque of the motor is deduced and calculated,and the law of the influence of the rotor design parameters on the motor torque is obtained.Then,under the actual operation condition of electric vehicle,the weak magnetic performance of the motor is analyzed,and the constraint conditions of the weak magnetic operation of the motor are obtained.By comparing the terminal voltage,torque,output power and high efficiency region of PMA-SynRM and IPMSM,it is concluded that the electromagnetic performance of PMA-SynRM is better than that of IPMSM in weak magnetic state.When the electric vehicle is running in peak condition,the permanent magnet is easy to be irreversibly demagnetized.Through the analysis of armature reaction and demagnetization causedby temperature rise,the demagnetization region and law of permanent magnet are obtained.From the point of demagnetization rate,comparing IPMSM and PMA-SynRM,it is concluded that PMA-SynRM with lower permanent magnet torque can obtain better demagnetization performance.Furthermore,the change of air gap magnetic field and torque is analyzed under the condition of loss of excitation.In order to further improve the anti demagnetization performance of the motor,the hybrid permanent magnet scheme is adopted.The influence of the ratio of two kinds of permanent magnet materials on the torque and demagnetization rate of the motor is analyzed,and the optimal rotor structure is obtained.