Research On Power Density Of In-wheel Motor For Electric Vehicle

With the increasing attention of energy and environmental problems,electric vehicles have made rapid development as a clean,environmentally friendly,efficient,renewable and recyclable vehicle,which has become the main trend of the development of the automobile industry.The in-wheel motor drive system has become one of the core technologies of electric vehicles with its unique advantages,which is an important research focus and development direction in the field of electric vehicle drive systems.However,because the in-wheel motor is installed in the rim,its volume is limited by the size of the rim,which cannot be designed to be too large.So its output power is limited,which is difficult to meet the high torque demand of the electric vehicle.In addition,the in-wheel motor will increase the unsprung mass of the electric vehicle.Therefore,it is an urgent problem to improve the power density.In this paper,the external rotor permanent magnet synchronous in-wheel motor for electric vehicles was modeled as a research object,its power density was studied under the premise of meeting the requirements of the drive system.Firstly,in this paper,the field-circuit coupling model of system driven by in-wheel motor for electric vehicle was established based on the finite element simulation software simplore and maxwell.The correctness of the finite element model and its modeling method established in this paper was verified by the performance of the no-load start-up,back-EMF and efficiency map measured by the experimental bench.Based on the model,the performance of the drive system such as start-up,load,and speed change was studied.It was proved that the drive system has strong starting,loading,variable speed,dynamic response and anti-jamming capability.Secondly,in order to study the power density of the in-wheel motor more quickly,conveniently and accurately,an analytical model of a surface mounted permanent magnet in-wheel motor was established in two-dimensional polar coordinates based on the Fourier series method.The model not only accounts for the specific size of the armature slot and the tip of the motor,but also its calculation accuracy is comparable to the finite element.Then,based on the model established in this paper,the influence of the structural parameters,the magnetic circuit structure of the rotor and the permanent magnet material on the power density of the in-wheel motor was studied.In addition,the auxiliary slot/teeth subdomain was added based on the analytical model established in this paper,and the model was verified by finite element.Then the influence of the parameters of the auxiliary slot on the cogging torque was studied based on the model,and the cogging torque of the motor was weakened.Finally,the comprehensive performance of the motor was calculated by the optimized motor parameters and the motor parameters which had changed the permanent magnet material.The results showed that optimizing the motor parameters and changing the permanent magnet material can increase the power density of the motor by 11.6% and 52.4% respectively when the motor mass is almost constant and the efficiency is improved.Finally,the magnetic field distribution of the segmented Halbach array permanent magnet motor was analyzed based on the analytical method,and the model was verified by finite element method.Then based on the analytical model,the power density of the Halbach array permanent magnet motor was studied.In the case of satisfying the requirements of the drive system,various factors such as mass,torque,and cost were taken into consideration.The appropriate parameters were selected to increase the efficiency and power density increased by 1.5% and 28% respectively in the case that the motor had little increase in the mass.