Analysis And Design Of Novel Fractional-slot Concentrated Winding Permanent Magnet In-wheel Machines

Due to the simple transmission structure and high transmission efficiency,in-wheel drive systems have become a hot point in the field of electrical machines.This dissertation presents a brief survey on the research status of in-wheel machine systems,and summarizes the directions of future research.The scope of this dissertation is to improve torque performance of in-wheel machines by renovating their topologies.The main contributions and contents of this dissertation are as follows:1.Based on the air-gap field modulation(AFM)theory,a general winding model of fractional-slot concentrated winding(FSCW)permanent magnet(PM)machines is proposed,which can handle the winding calculations of both rotor-magnet and stator-magnet machines.It is the first time that the relationship among the temporal back electromotive force(EMF)harmonics and spatial flux density harmonics in FSCW-PM machines is explained through a purly mathematical modeling.The general calculation formulae of the pitch factor and the distribution factor are deduced based on this mathematical model,which is the theoretical foundation of design of in-wheel machines.2.The structure of existing flux-switching permanent magnet(FSPM)in-wheel machines is renovated to improve the torque performance,by replacing “rectangular magnet + rectangular stator tooth” structure with “wedge-shaped magnet + wedge-shaped stator tooth” structure.To guide the future design,a torquesizing equation is derived and the fundamental optimization flow chart is introduced.According to the comparison with surface-mounted permanent magnet(SPM)in-wheel machines,it is found that the novel FSPM in-wheel machines is suitable for the light in-wheel traction applications.3.With the high-current injection,the magnetic saturation in FSPM in-wheel machines becomes terrible,which limits the over-load capability of in-wheel drive systems,resulting in a weak acceleration and climbing performance.By removing the magnets from stator to rotor,the FSPM in-wheel machines is transformed into a novel kind of modular spoke-type permanent magnet(MSTPM)in-wheel machines.According to the comparison with SPM in-wheel machines,it is found that the MSTPM in-wheel machines is suitable for both light and heavy in-wheel traction applications.4.In addition to explaining the fundamental working mechanism of MSTPM in-wheel machines,an analytical air-gap flux density model is built,and then,the special electromagnetic phenomenon is introduced,and the fundamental optimization design procedure is proposed.Further,two different magnetization modes for the MSTPM in-wheel machines are investigated,including M-I type and M-II type.Through building the magnetizing magnetomotive force(MMF)-permeance model,the difference between the optimal structures of the MSTPM in-wheel machines with two different magnetization modes are analyzed.Based on the comparative study,the merits and demerits of two types of MSTPM in-wheel machines are concluded.5.A general mathematical model of two types of MSTPM in-wheel machines is established to normalize the analysis of MSTPM in-wheel machines.Based on the AFM theory,the real machine topology is translated into the modulation topology.Then,the magnetizing source and the modulators are mathematically modeled,and the air-gap flux density distribution function is further obtained.Taking the specific inner-stator structure and winding layout into consideration,the slot leakage inductance and airgap inductance are deduced.