Multi-objective Optimal Design Of Torque Characteristics Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)meets the requirements of high precision,low energy consumption and economy.In the research of PMSM,reducing torque ripple rate and increasing output torque are crucial design indicators.The rotor poles of surface-mounted PMSM can adopt Halbach permanent magnet arrays to achieve a more sinusoidal air-gap flux field with a higher amplitude of the fundamental wave of the flux density,and effectively reduce the harmonic content of the air gap.The self-shielding effect of the Halbach permanent magnet array can achieve the flux concentration effect on one side of the permanent magnets(PMs),so that the rotor yoke can be as thin as possible,which helps to reduce the mass of the rotor and increase the torque density.The rotor poles of the traditional Halbach array structure are evenly segmented,and the permanent magnet blocks are closely connected without leaving any gaps.The angle between the magnetization directions between two adjacent permanent magnet blocks causes a part of harmonics to be introduced into the air-gap flux density.The introduced harmonic content which resulting in a large torque ripple is closely related to the angle between the magnetization directions between the permanent magnet blocks.Therefore,for the wide pole arc Halbach array PMSM,it is very important to suppress this part of harmonic.In this paper,multi-objective optimization design of halbach array PMSM is taken as the main researching object.The research of this paper as follow:First,this paper presents the topology of the Halbach array with inner arc eccentricity and pole partition.The influence of key design variables on the three performance indicators include no-load air-gap flux density waveform and harmonic content,cogging torque,and output torque of the finite element analysis(FEA)model are compared and analyzed.Mathematical surrogate models of the output torque and cogging torque on the eccentricity of the inner and outer arcs,the pole arc coefficient,and the magnetization angle of the Halbach array are established respectively.Multiobjective optimization is performed by applying non-dominated genetic algorithm(NSGA II).After the optimization is completed,the Pareto front is analyzed,and the torque characteristics of traditional radial magnetized PMSM and the Halbach array PMSM with inner arc eccentricity and pole partition are compared and analyzed.Secondly,this paper proposes two types of block-spaced halbach arrays,namely a triangular-spaced halbach array and a uniformly-spaced halbach array.The stator structure remains unchanged,and the ratio of output torque to rotor mass(Tor-RM)is proposed as an indicator of torque density.The effects of various key design parameters on the harmonic content of no-load air-gap flux density,torque ripple ratio and TorRM of the motor finite element model.Comparison and analysis of the difference in torque characteristics between motor models with two spaced halbach array,radial magnetized PMSM and traditional Halbach array PMSM.Compared with the traditional Halbach array,the block-spaced Halbach array proposed in this paper can effectively improve the waveform of the air gap flux density and suppress the harmonics caused by the difference in the magnetization angle of the PM block.Thereby,it has an excellent improvement effect on torque ripple ratio.Then,a non-uniformly-spaced Halbach array structure is proposed in this paper.Based on orthogonal experiments and parameter sensitivity analysis,the effects of key design parameters on four performance indicators of cogging torque,average output torque,torque ripple,and torque ripple ratio of the finite element model of the motor would studied.Based on MATLAB,the mathematical models of the average torque and torque ripple ratio with respect to the structural design parameters are established,and the accuracy and reliability of the mathematical models are verified by the results of orthogonal experiments.The main gap,the secondary gap,and the center angle of the main magnetic block have a significant effect on the torque ripple ratio of the PMSM.The average output torque of the motor is obviously affected by the slot opening width and the center angle of the main magnetic block.Finally,NSGA-II is used for global optimization.Through the finite element analysis of the optimal sample,the improvement effect of the non-uniformly-spaced Halbach array proposed in this paper on the torque performance of the motor is verified.Finally,through a comparative analysis of several optimization design schemes,it is known that the torque ripple ratio of the Halbach array with inner arc eccentricity and pole partition,triangular-spaced halbach array,a uniformly-spaced halbach array and non-uniformly-spaced Halbach array are effectively improved.The torque ripple ratio is reduced from 18.6% of the radial magnetized motor to 1.56% to 2.45%,and the power-to-mass ratio is increased from 0.4412 k W/kg of the radial magnetized motor to0.5173 k W/kg to 0.5349 k W/kg.A complete set of processes for the design and optimization of PMSMs and a new optimization method for the motor torque characteristics are provided in this paper.It is of great significance to study the optimal design of torque characteristics of permanent magnet synchronous motors based on Halbach array and wide pole arc...