Electromagnetic Analysis And Topology Investigation Of Novel Dual-armature Flux Reversal Machine

With the rapid development of economy and industrial technology,electric machine as the core part in many fields such as wind power generation,electric vehicles and aerospace is facing higher and higher performance requirements.Electric machine with high torque density,high efficiency and high reliability becomes a hot topic in current research and also a developing trend in the future.As a type of stator permanent magnet(PM)machines,flux reversal machines(FRMs)featuring simple structure,high torque density and low risk of PM irreversible demagnetization have great potential in the fields of electric vehicles,low speed servo systems and wind power generation.However,FRMs suffer from large equivalent airgap length since the PMs are mounted on the surface of stator teeth,which limits the torque improvement of FRMs.So far,many scholars both at home and abroad have investigated the new topologies of FRMs to enhance the torque performance or improve the fault tolerance capability,but few research can achieve both of these goals.Thus,the FRMs with high performance still have great research potential.This thesis proposes a novel dual armature FRM(DA-FRM)with two sets of independent armature windings accommodated in stator and rotor slots,respectively,which takes full advantage of rotor space and the proposed structure can not only greatly improve the torque density,but also has better fault tolerance capability.The working principles,harmonic components,design and optimization as well as topologies of the novel DA-FRM are detailedly investigated in this thesis.First,the advantages and shortcomings of FRMs are introduced and their potential applications are identified.Besides,the research status of FRMs are summarized from three aspects,i.e.,theoretical analysis and modeling,design optimization and performance improvement,and topology development.Since the novel DA-FRM proposed in this thesis has three magnetic fields,i.e.,magnet field,stator and rotor armature magnetic fields,its working principles are different from conventional FRM.Thus,the working principles of DA-FRM are firstly elaborated in details.Then,based on the magnetic motive force(MMF)-permeance model,the expressions of airgap flux densities are derived and the main harmonic components are revealed.Moreover,the finite element(FE)method is used to validate the accuracy of the above analytical expressions.In addition,the interactions among the three magnetic fields in DA-FRM are analyzed and the main harmonic components that contribute to the torque production are also investigated.After that,the design and optimization of DA-FRM are deeply researched.The influences of key structural parameters(including split ratio,stator and rotor slot opening ratio,magnet thickness and stator tooth width)on the torque performance of DA-FRM are studied,which provide practical guidance for key parameter selections.Then,the electromagnetic performances of optimized DA-FRM are analyzed including no-load and on-load characteristics,together with PM demagnetization characteristics,and its performances are also compared with the conventional FRM and the surface mounted PM(SPM)machine.Additionally,a DA-FRM prototype is fabricated and tested to verify the above analysis.In order to further improve the torque density,three novel DA-FRMs are proposed in this thesis,i.e.,DA-FRM with consequent pole structure,DA-FRM with PMs magnetized in NSNS pattern and DA-FRM with Halbach array magnets in stator slot opening.The working principles of these three novel DA-FRMs are addressed and the structural parameters are optimized.Their electromagnetic performances after optimization are analyzed and compared with the conventional FRMs as well as SPM machines.Finally,three prototypes are manufactured and tested to validate the aforementioned analysis.