Research On Electromagnetism Of Modular Outer-rotor Flux-switching Permanent-magnet Motor

Modular outer-rotor flux-switching permanent-magnet motor(MOR-FSPM)combines the advantages of three kinds of motors: modular motor,outer-rotor motor,flux-switching motor.Modular structure can improve the self-inductance and reduce the mutual-inductance of motor,thus enhancing the fault tolerance capability.The outer-rotor structure can omit the reducer and differential gear to provide additional space for cooling system and control system,so that motor can be applied to direct drive field.Flux-switching permanent-magnet motor(FSPM)has the characteristics of sinusoidal flux linkage,high torque density and so on.In the field of direct drive that requires high efficiency and reliability,MOR-FSPM has far-reaching significance and broad application prospects,such as electric vehicle(EV),wind power generation,aerospace and ship propulsion.In this paper,the development and research status of FSPM,outer-rotor FSPM and modular FSPM are summarized,the method of combining theoretical analysis with finite element simulation is adopted to research MORFSPM.Firstly,this paper introduces the mechanical structure of MOR-FSPM,especially the stator,and analyzes the operating principle of MOR-FSPM from the view of generator.Based on the principle of magnetic gear,the operation principle of MOR-FSPM is analyzed from the view of motor.The pole logarithm of the motor windings,the logarithm of the rotor pole and the synchronous speed of the windings are defined.The pole logarithm of effective harmonic for producing the stable torque is derived.Secondly,the calculation scheme of main parameters in MOR-FSPM is determined.According to the characteristics of modular stator structure,the constraints of stator parameters are established when MOR-FSPM obtains symmetric three-phase EMF.The influences of different pole/slot combinations on the torque characteristic of MOR-FSPM are analyzed.The finite element models of different pole/slot combinations are established,and the related characteristics are analyzed and compared.The 10-pole/12-slot MOR-FSPM is selected to optimize the main parameters.Thirdly,compared to the conditional outer-rotor flux-switching motor(COR-FSPM),the magnetic circuit and structure of MOR-FSPM are changed.In order to make a reasonable evaluation of the MOR-FSPM performance,the basic performances of MOR-FSPM and COR-FSPM are compared,including air-gap magnetic density,cogging torque and so on.Aiming at the key motor performances in the field of EV,the utilization of PM,fault tolerance capability,field weakening capability,loss and efficiency of MOR-FSPM and COR-FSPM are compared.Finally,in the MOR-FSPM,the weakening effect of two kinds of rotor two-step skewing methods on the cogging torque and torque ripple is studied.The effect of this two methods on cogging torque,torque ripple and back EMF are derived.2-D and 3-D finite element methods(FEM)are adopted to verify and compare the effect of the two methods.