Research And Design Of Direct-Drive In-Wheel Motors For Electric Vehicles

In-Wheel motor has become a new trend in the development of electric vehicles,due to its inherent advantages in terms of independent control,high efficiency,etc.However,due to the requirement of high performance if electric vehicle(EV)and the limited installation space,high torque density,excellent heat dissipation and overload capabilities are essential in the design of in wheel motors.In this paper,the design parameters are determined according to the requirement of the EV.Then the principles and design methods of Permanent-Magnet Synchronous Motor(PMSM)and Flux-Modulated Permanent-Magnet Motor(FMPM)motors are introduced.The influences of the structure parameters on the performance of both motors are evaluated.Consequently,these two kinds of direct-drive in-wheel motors are designed.Using the Finite Element Analysis(FEA)and analytic analysis,the air-gap magnetic flux density,back EMF and torque of each motor are investigated.Also,the impacts on cogging torque of slot opening width,pole arc coefficient and skew under different slot/pole combinations are explored.Then the methods for cogging torque optimization with their applications and effects on performance of both motors are summarized.Under the condition that both motors are designed to meet the same rated performance with same back EMF,current density and copper loss,this paper analyses and compares the torque density,flux-weakening performance,power factor,loss and efficiency of PMSM and FMPM.Moreover,the temperature rise under different load of both motors are checked considering the worst case scenario.Finally,the performance of PMSM and FMPM with the same size are compared.The results show that two kinds of motors have their own advantages and disadvantages.To meet the same torque performance,compared with the PMSM,FMPM has smaller size,lower material cost,wider speed range,fewer torque ripple,but lower power factor,higher iron loss due to the high frequency of stator current.