Design And Analysis Of In-wheel Outer Rotor Flux Switching Permanent Magnet Machine

As a new type of permanent magnet motors,flux switching permanent magnet machines(FSPMMs)have some advantages,such as high torque density,energy density and strong fault redundancy capability due to their extremely simple rotor structure and the advantages of fractional-slot concentrated windings(FSCWs).FSPMMs have attracted considerable interest from academia and industry not only because of their essentially sinusoidal phase back electromotive force(back-EMF)waveform,but also their high electromagnetic torque/power densities.At the same time,in-wheel motors drive system has attracted more and more attention becasuse it can omit many driving parts improve the transmission efficiency and save space for vehicles.Firstly,research background and significance of FSPMMs and their research situation at home and abroad would be illustrated in this paper.At the same time,the classification and characteristics of in-wheel motor drive system and drive motors would be introduced in detail.Secondly,the structural characteristics and working principle of FSPMMs are elaborated for the subsequent optimization of the motor design.The mathematical model of the FSPMM in d-q frame is deduced and the relationship between the main parameters of FSPMMs is finally obtained.Then,a three-phase 48/56 slot/poles flux switching permanent magnet in-wheel motor(OR-FSPM)is designed and optimized for its air gap length,split ratio,stator and rotor width and yoke thickness.In order to improve the performance of the OR-FSPM,the effect of FSCWs with double and four-layer winding configuration in FSPMMs is fully investigated in this paper.First of all,two three-phase 12/13 slot/poles FSPMMs were designed with two-layer and four-layer FSCWs,respectively.Under the same contrast conditions,it can be seen that the four-layer FSCWs can cancel the partial harmonics and reduce the total harmonic distortion(THD)of the back electromotive force(back-EMF)based on finite element analysis(FEA).As a result,the back EMF waveform can be more sinusoidal.In additon,the four-layer FSCWs can also reduce the solid loss in PMs due to the reduction of harmonic components in stator MMF.What is more,the higher the speed,the more obvious effect.Finally,four-layer FSCWs is applied into the OR-FSPM and then is compared with a three-phase 18/16 slot/poles surfaced mounted permanent magnet in-wheel motor(OR-SPM).On the suppose of the constant outside diameter,current density and rated speed based on comprehensive simulations and theoretical analysis,it can be concluded that the OR-FSPM with four-layer FSCWs has some advantages of the lower THD of no-load back-EMF,less losses,less usage of PMs and silicon steel,lower temperature rise,higher efficiency and higher torque/power densities.Comprehensive investigations exhibit the proposed machine is one ideal candidate for the in-wheel EV drive system.