Research On Electromagnetic And Vibration Performance Of Modular Permanent Magnet In-wheel Motor

In-wheel motors and drive systems have recently become a research hotspot on electric vehicles because they have such advantages as structure simplicity,control flexibility and high transmission efficiency.Applied to a special vehicle,the in-wheel motor is normally required to have not only high torque overload and flux-weakening capacity,but also high reliability and fault tolerance.Therefore,this paper combines the modular fault-tolerant topology with the in-wheel motor to improve the operating reliability.The special problems existing in the design process of the machine brought about by modular structure need to be studied.As a kind of fault-tolerant machine,the modular motor is required to study the modifications of electromagnetic performance and certain compensation measures that need to be taken during fault operations.In addition,changes in the vibration characteristics under fault operations may affect the smoothness of the vehicle and reduce motor's operating reliability.Therefore,it is of vital importance to get accurate prediction of the vibration characteristics under normal,fault,and fault-tolerant operations.This paper implements research on aspects including the motor design,electromagnetic performance,fault tolerance,electromagnetic force analysis and vibration characteristics prediction.The main research work are as follows:Firstly,based on the working principle and advantages of the modular fault-tolerant topology,the pros and cons of various design schemes in terms of the number of modules and pole-slot combinations are discussed in detail,combined with the in-wheel motor's performance requirements.Then the optimal design principles are given.Since the modular motor has unique performance defects,deep investigations has been made on the effect of different pole-slot combinations,rotor skewing,and different winding configurations on the performance.The primary design methods are thus summarized in order to provide references for designers.According to the final design schemes,the output performance relationships between the part-module operation and whole machine operation are studied.Secondly,due to the high fault-tolerance requirements,the electromagnetic performance of the modular motor under different open-circuit fault operations is studied.The post-fault performance variation is analyzed.The torque characteristics of directly cutting down faulty module and magetomotive force compensation are compared when the modular motor is dealing with one-phase open-circuit fault.As for inter-module open-circuit faults,a method named winding reconstruction is proposed to improve the winding utilization and torque charateristics.The feasibility of the magnetomotive force compensation and the winding reconstruction method is verified by a modular motor prototype experiment.Thirdly,the expressions of the airgap radial force density under normal,fault and fault-tolerant operating conditions are theoretically derived.Based on the the winding magnetomotive force modification under fault and fault-tolerant operations,those expressions are amended.The time and space harmonic contents are analyzed.The finite element model of the modular motor is established to obtain the force density distributions under different working conditions and the harmonic contents,by which the accuracy of the analytical results are verified.Finally,to accurately predict the vibration characteristics of the modular motor,the precise structural model of the stator system is established,with modes and natural frequencies studied.The vibration characteristics of part-module operations are studied based on transient analysis and harmonic analysis.Quantititave comparison of the vibration performances in normal,fault and fault-tolerant operations under different working conditions are made for analyzing the variation of harmonic contents at different frequencies.Focusing on one-phase open-circuit faults,the method of adjacent modules compensation is proposed to suppress electromagnetic vibration.Through vibration experiments under different operating conditions,the simulation results are verified.