Design And Research Of Negative-Saliency Less-Rare-Earth Hybrid Permanent Magnet Synchronous Motor

The development of new energy vehicles is a strategic initiative to cope with the energy crisis and promote green development.Rare earth permanent magnet（PM）motors are adopted by most automobile manufacturers as driving motors and used in commercial electric vehicles because of their high efficiency,energy-saving,and compact structure.However,the high price and scarcity of rare earth permanent magnet materials add uncertainty to the large-scale promotion and application of new energy vehicles.The research on less-rare-earth hybrid PM motors can alleviate the dependence of permanent magnet motors on rare-earth materials,which is of great significance to promote the sustainable development of the new energy automobile industry.However,the shortcomings of low-coercive-force magnets irreversible demagnetization in less-rare-earth hybrid PM motors and the inherent problem of narrower speed range of PM motors,which limits its further application.Therefore,a new negative-saliency less-rare-earth hybrid permanent magnet synchronous motor（NSLRE-PMSM）is proposed based on traditional interior permanent magnet motor in this thesis.The motor structure not only reduces the consumption of rare earth materials,but also the torque characteristics of the motor are not affected,the utilization ratio of permanent magnets is further improved.At the same time,the anti-demagnetization ability of ferrite is improved by negative-saliency characteristic,and the flux-weakening performance of the motor is also improved.A stratified multiobjective optimization method based on comprehensive sensitivity analysis is proposed to efficiently and accurately optimize torque performance of NSLRE-PMSM.In respond to accurately analyze and evaluate the anti-demagnetization ability of permanent magnets,a demagnetization analysis method about temperature for permanent magnets is proposed.（1）The general design flow of NSLRE-PMSM is proposed,according to the performance requirements for the potential application scenarios,combined with dimensional equation and related design experience,the ratio of pole slot combination,main structure dimensions and the stator slot design of the motor are determined.The preliminary rotor topology of NSLRE-PMSM is carried out based on the rotor topologies and magnetic circuit characteristics of the two kinds of interior PM motors.According to the design constraints,the size of the two permanent magnets is theoretically analyzed to complete the initial design of the motor.（2）On the basis of the preliminary motor structure,a stratified multi-objective optimization method based on comprehensive sensitivity analysis is proposed,the multiobjective optimization of NSLRE-PMSM is carried out based the method to obtain the optimal model.The sensitivity of optimization variables is determined through comprehensive sensitivity analysis,and the optimization variables are divided into weak sensitive layer and strong sensitive layer according to the analysis results.The value of the optimization variables in the weak sensitive layer is kept,and the optimization variables with strong sensitivity are optimized.The Least Squares Support Vector Machine（LSSVM）fitting model is established to determine the functional relationship between optimization objectives and highly sensitive variables.Chaotic Cultural Differential Evolution Algorithm（CCDE）is used for multi-objective optimization to obtain the optimal size combination of the motor.（3）The finite element method is used to analyze and evaluate the optimal NSLREPMSM and reference motors,including no-load air gap flux density and back electromotive force characteristics,magnetic field distribution,torque characteristic and inductance characteristic.In addition,the utilization ratio of permanent magnets,the flux-weakening capability and the demagnetization risk of two permanent magnets are analyzed,to verify the validity of motor design and preferable performances.（4）The temperature field of NSLRE-PMSM is analyzed,and a new demagnetization analysis method considering temperature rise of permanent magnet is proposed.The steadystate temperature field analysis and transient-state temperature field analysis are carried out by calculating the loss and thermal parameters of each component of NSLRE-PMSM,the temperature distribution of the whole and parts of NSLRE-PMSM is investigated,and the flux density of permanent magnet at high temperature is analyzed.