Research On A 4KW In-Wheel Motor System Used For Electric Vehicle

Electric vehicle technology is developing rapidly in recent years,the concept vehicle from many automobile manufacturers shows that direct drive technology is the main direction of electric vehicle development.Direct drive in-wheel motor,which takes out a lot of mechanical structure,has the characteristics of rapid dynamic response,high power density,high efficiency and high reliability.However,the performance optimization,the control technique and the system fault diagnosis of the in-wheel motor system still need to be further studied.Focusing on these issues,The electromagnetic performance optimization,temperature field analysis,vector control and demagnetization fault diagnosis of in-wheel motor are studied in this paper,which takes a 4kW in-wheel motor as an example.The major works are summarized as follows:Firstly,the electromagnetic structure design and performance optimization of 4kW in-wheel motor are studied.For the purpose of reducing motor volume and heating value,reducing motor torque ripple,the selection methods of the winding form,yoke thickness,axial length and slot width of hub motor are given,and the preliminary electromagnetic scheme of 4kW in-wheel motor is established.The method of magnetic pole eccentricity and combined pole is employed to further reduce the torque ripple,reduce the heating value and the motor cost,improve the efficiency.The performances of magnetic pole eccentricity motor,combined magnetic pole eccentricity motor and main magnetic pole eccentricity motor are compared and analyzed,and the main magnetic pole eccentricity motor is selected as the final scheme of 4kW in-wheel motor.Secondly,aiming at the problem of the bad heat dissipation of in-wheel motor,the temperature rise and temperature distribution of 4kW in-wheel motor at rated working condition and peak working condition are analyzed.The equivalent 3D temperature field model is established,the boundary conditions are given,and the heat rate,the thermal conductivities and the heat transfer coefficient are calculated.The variation in steady state temperature of four kinds of magnetic pole motor at rated working condition and the variation in transient temperature at peak working condition are compared and analyzed.Thirdly,aiming at the problem of the light power in-wheel motor has large torque ripple which uses rectangular-current control,the vector control method of in-wheel motor based on hall position sensor is studied.The high frequency square wave injection method is employed to revise hall position signal at low speed region,and the rotor position observer based on EKF is employed to revise hall position signal at high speed region,therefore the rotor position can be obtained accuratly in real time,and the vector control of in-wheel motor based on hall position sensor is realized.Finally,aiming at the problem of demagnetization fault which in-wheel motor often occurs,the diagnostic methods of in-wheel motor's demagnetization fault is studied.The mathematical model of in-wheel motor's demagnetization fault is established and the characteristics of in-wheel motor's demagnetization fault are simulated.A permanent magnet flux observer based on EKF is established to diagnose the uniform loss of magnetism fault of in-wheel motor,and the EKF permanent magnet flux observer is improved to solve the problem of large fluctuation of EKF permanent magnet flux observer in low-speed region.