Research On Performance Of Permanent Magnet Wheel Motor For Electric Vehicle

With the increasing problems of climate,environment and energy,the development of electric vehicles,which is the substitute of traditional internal combustion engine vehicles,is developing more and more rapidly.The driving method of the hub motor as the latest electric vehicle driving technology has been widely concerned by scholars at home and abroad.As the most important component of the hub motor drive system,the permanent magnet hub motor puts forward higher requirements on its power density,torque density and torque ripple.At present,the research on permanent magnet hub motor mainly adopts finite element method and analytical method.The finite element method can deal with complex structure model,and can combine the control circuit to analyze the dynamic performance of the motor,but the cycle is longer and it is not convenient for regularity research.The analytical method can make up for this shortcoming,and has the characteristics of high calculation accuracy and short cycle.Therefore,this paper uses the finite element method to study the performance of the permanent magnet hub motor,and uses the analytical method to analyze the influence law of the electromagnetic performance and improve the structure of the permanent magnet hub motor to improve the performance of the motor.Aiming at the permanent magnet hub motor studied in this paper,a finite element model is established in the analysis software Maxwell,and an analytical model considering the relative permeability of the magnetically permeable material is established based on the complex form Fourier series and Cauchy product theorem.The electromagnetic properties of the permanent magnet hub motor are analyzed using two models.The accuracy of the analytical model is verified by the prediction results of the finite element model.At the same time,the outer circuit control model of the hub motor adopting SVPWM control strategy and double closed-loop control mode is built in the finite element software Simplorer.Based on the Simeror-Maxwell motor drive system joint simulation model,the dynamic performance of the hub motor no-load start,acceleration and loading is analyzed.Finally,the correctness of the finite element model and the analytical model is verified by the performance of the no-load back EMF and the motor efficiency map using the permanent magnet hub motor test bench.The analytical model is used to calculate the high efficiency and can consider the magnetic permeability of ferromagnetic materials.Firstly,the influence of magnetic permeability on the electromagnetic properties of permanent magnet hub motors is studied.The research shows that as the relative magnetic permeability of the magnetically permeable material becomes smaller,the radial component of the magnetic load and air gap of the motor decreases and the tangential component increases.At the same time,the smaller the relative permeability value causes the flux linkage,back EMF and output torque to become smaller,and the output torque fluctuation increases.Secondly,based on the analytical model,the influence of structural parameters such as slot opening width,pole arc coefficient and air gap length on the electromagnetic performance of permanent magnet hub motor is predicted,and the motor structure parameters are improved.In order to further improve the performance of the permanent magnet hub motor,the topological structure of the permanent magnet was improved on the basis of the improvement of the structural parameters,and the block was changed into a Halbach structure.Based on the analytical model,the influence of the number of blocks per pole on the electromagnetic performance is discussed,and the performance of the block Halbach permanent magnet hub motor is predicted.The research shows that compared with the original motor,the amplitude of the fundamental wave of the air gap magnetic induction of the improved motor is obviously increased,and the harmonics are effectively reduced;the cogging torque of the motor is reduced by 36.5%;the average value of the output torque is increased.With 21.7%,the torque ripple is reduced to only 3.44%.Comparing the loss distribution of the motor under the same load,the study found that the block Halbach permanent magnet structure can reduce the loss while further improving its electromagnetic performance.Finally,the efficiency map of the improved permanent magnet hub motor is calculated.The results show that the highest efficiency of the improved motor is 96%,which is 3.2% higher than the original structure.