Research On Modeling And Performance Of In-wheel Motor For Electric Vehicles

Mileage seriously restricts the development of distributed drive electric vehicle technology,and is a technical bottleneck before a large number of applications.Because the driving motor is integrated into the wheels,the mass of the sprung mass increases,which also has an important influence on the ride comfort of electric vehicles.As one of the core components of the distributed drive electric vehicle,the permanent magnet in-wheel motor has some outstanding problems,such as the torque density is difficult to be raised,the mechanism of torque ripple is complex and difficult to restrain.It has great influence on the light weight and ride comfort of the electric vehicle.Although the performance of the permanent magnet in-wheel motor can be analyzed with finite element,and the effects of end effect,core saturation and material nonlinearity on the performance of the in-wheel motor are considered,but the modeling is complex and the calculation period is long,it is difficult to study the influence of design parameters on the performance of the in-wheel motor.The analytical method has the advantages of fast calculation speed,clear physical concept and no repeated modeling when changing the design parameters.However,most of the existing analytical methods have simplified the motor model,such as ignoring the stator tip,the armature winding is equivalent to the current loop,and the properties of the ferromagnetic material,etc.The calculation accuracy is not exact.For this reason,a more accurate analytical modeling method is developed to lay the foundation for solving the operational quality problems of power density and torque ripple of permanent magnet in-wheel motor.For the permanent magnet embedded rotor in-wheel motor,the model of the drive control system is established in this paper,and the torque,power,efficiency and temperature rise are calculated,and the validity of the finite element modeling method is verified by the bench test.In order to study and improve the performance of the in-wheel motor,an accurate analytical model is established,and the effect of the stator tooth tip on the distribution of the air gap magnetic field is considered.Based on this analytical model,the performance of the air gap magnetic density,magnetic chain,back EMF,cogging torque and output torque are predicted.The finite element method is used to verify the correctness of the analytical model.Compared with the simplified models that ignores the stator tooth tip,The analytical model considering the stator tooth tip is more accurate,and the error of the cogging torque,torque ripple and the average output torque are reduced from 499.68%,216.24% and 11.97% to 9.8%,6.55% and 0.9%,respectively.Based on the analytical model,the influence of structural parameters on the in-wheel motor performance is studied.A matching scheme is proposed to optimize the performance of the in-wheel motor.The method of opening the auxiliary slot on the stator tooth is proposed to reduce the torque fluctuation of the in-wheel motor.The model of the in-wheel motor solution with the auxiliary slot on the stator tooth is established,and the accuracy of the model is verified by the finite element method..The influence of the auxiliary slot parameters on the performance of the wheel motor is studied.It is found that when two auxiliary grooves are opened,the cogging torque and torque ripple can be greatly weakened by optimizing the slot parameters.The study shows that when the auxiliary groove width is 0.835 times the width of the stator slot opening and the depth is 1 mm,the average output torque is only reduced by 3.35%,and the torque ripple is greatly reduced by 26.95%.In order to further reduce the torque ripple and increase the torque density of the in-wheel motor,the Halbach array is introduced to replace the embedded permanent magnet structure.A permanent magnet in-wheel motor with Halbach array is designed and its analytical model is established.Based on this method,the influence of design parameters on the performance of the in-wheel motor is discussed and the optimization results are obtained.Compared with the original motor,the torque ripple was greatly reduced by 96.03%,and the output torque average increased by 17.26%.In addition,the influence of magnetic permeability of ferromagnetic material on motor performance is studied.An analytical model of Halbach array in-wheel motor with magnetic permeability is proposed.The influence of magnetic saturation effect on motor performance is taken into account,and it is possible to study the performance of in-wheel motors in unsaturated,transition saturated and saturated conditions.The research shows that when the relative permeability is less than 7000,the output torque varies greatly with relative permeability,and the output torque is almost unchanged when the relative permeability is greater than 7000.