| Yokeless and Segmented Armature Axial Flux Motor（YASA）has the advantages of short axial length,high torque density and high efficiency owing to the structural characteristics of axial-flux permanent motor,but also has the characteristics of small stator core loss,short winding end and high slot fullness which consistent with the future development trend of electric vehicle drive motor.However,due to the soaring price of rare earth permanent magnet materials in recent years,the cost of rare earth permanent magnet motor has risen rapidly,which has hindered its application and promotion.Therefore,in this thesis,the YASA motor for electric vehicles is designed as baseline motor,and proposed a topology of hybrid excitation rotor of less-rare earth motor to reduce the consumption of rare earth permanent magnet while maintain the requirement of torque density of electric vehicles,so as to reduce the cost.And the Multi-objective Cultural Differential Evolution algorithm（MOCDE）is used to optimize the motor structure,which further reduce the amount of rare earth and torque ripple.According to the requirements of electric vehicle drive motor for flux-weakening speed regulation range,an efficient and accurate hybrid flux-weakening analysis method is proposed to verify that the motor has excellent flux-weakening capability.The main works are as follows:（1）By analyzing the characteristics of different topologies of axial flux permanent,and select YASA motor as the research object of this thesis.According to the performance index requirements of electric vehicle drive motor,the preset parameters are determined by analyzing the magnetic circuit structure and design experience.Finally,according to the preset parameters and size equation,the structural parameters such as stator and rotor size and air gap length of YASA motor are obtained,and the rationality of the design is verified by finite element modeling and simulation.（2）A rotor structure of Less-Rare-Earth Yokeless and Segmented Armature Axial Flux Motor（LRE-YASA）is proposed which radical combines surface-mounted rare earth permanent magnet with a Halbach array of mixed magnetic materials.Taking YASA motor as the baseline motor,the preliminary rotor structure design is determined by the principle of excitation source equivalence and the analysis of Halbach array magnetic field of mixed magnetic material,and proving rationality of the design by finite element simulation.（3）Based on the preliminary design scheme of LRE-YASA,the torque/rare earth permanent magnet consumption ratio and torque ripple are selected as optimization objectives and six closely related structural parameters are selected as optimization variables.The sample space is established through orthogonal experiment and the function fitting of the optimization objective is carried out by support vector machine.Finally,Multi-objective Cultural Differential Evolution algorithm（MOCDE）is used to optimize LRE-YASA motor,and pareto optimal solution set was obtained.The simulation results verify the accuracy of the algorithm and determine the optimal structure size of the motor.（4）According to the operation principle of LRE-YASA motor to select an appropriate stator current vector control strategy.Considering the influence of permanent magnet working point change,magnetic circuit saturation and cross-coupling effect on d-and qinductance during motor operation,a hybrid flux-weakening analysis method based on finite element transient field and analytical method is proposed to accurately and efficiently analyze the flux-weakening capability of LRE-YASA motor.It is verified that the optimized motor not only has high output torque at low speed,but also has sufficient flux-weakening capability. |
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