Theoretical Analysis And Topology Investigation Of Flux Reversal Permanent Magnet Machines

Many industries such as wind power,electric vehicle and rail transportation are growing rapidly these years.In these industries,motors with high torque density,small torque ripple,high reliability and efficiency are favorable.Flux reversal machines(FRMs)are one of the machine types that meet the above requirements.Permanent magnets(PMs)of FRMs are placed on the inner surface of the stator,which is easy for installation,and the rotor is a simple reluctance rotor which is suitable for high speed or high temperature operations.Besides,FRMs have the advantages of high power density,good fault tolerance,fast dynamic response and high efficiency.Therefore,they are suitable for many applications,especially electrical vehicles.In addition,FRMs operate based on the magnetic gearing effect,i.e.the rotor speed is much slower than the rotation of stator flux.Hence,FRMs can also be used in direct-drive applications,such as wind power and wave energy generations.However,the current research on the FRMs is mainly based on finite element algorithm(FEA),and the theoretical analysis on FRMs is not comprehensive.There are still a lot of basic theoretical issues including the analytical expressions,the generic design procedure and the systemic analysis methods need to be explored.This thesis will focus on the theoretical analysis and topology study of FRMs.The magnetic circuit model,the analytical method,the basic characteristics,the design method and the new topologies will be studied and analyzed.The organization of this thesis is as follows.First,in Chapterl,this thesis reviews the history of FRMs.From switched reluctance machines(SRMs)to the doubly salient permanent-magnet machines(DSPMs)and then the FRMs,the characteristics of FRMs are studied.Besides,applications and research status of FRMs are also summarized.Then,in Chapter 2,the magnetic field distributions for different rotor positions are analyzed,and a simplified magnetic circuit model is derivated.Moreover,based on the magnetic circuit model and the classical winding theory,the permanent magnet magnetic-motive force,specific airgap permeance,airgap flux density,back electromotive force,the pulsating torque and the average torque are studied systematically.In addition,this thesis also analyzes the reason why the power factor of FRMs is often low and introduces some effective ways to improve the power factor.Finally,FEA simulations verifies the accuracy of the calculated results from the derived analytical expressions.After the study of the magnetic circuit model and the electromagnetic characteristics,this thesis analyzes the design method of FRMs in Chapter 3.First,the relationship among the average torque and some key parameters of FRMs including the air gap diameter,stack length,electric loading and magnetic loading is derived.So the air gap diameter and stack length can be obtained from the average torque.Then,based on assumed flux densities,structural parameters of the stator and rotor can be calculated.Therefore,a generic design method of FRMs can be established.In addition,the influences of the structural parameters on the key electromagnetic performances(including the average torque,the cogging torque,the torque ripple,the power factor and the demagnetizing property of the PMs)are studied,and their optimal values are found,which provides an important guidance for key parameter selections,torque density improvement and pulsating torque minimization.Finally,in order to verify the proposed analytical design method and optimization theory,a regular FRM which is designed using the proposed method is built and tested.In order to further improve torque density,reduce torque ripple,enhance power factor and widen operating speed range,four new FRMs are presented in Chapter 4,i.e.consequent-pole FRM,C-core FRM,uniformed-PM FRM and hybrid excitation FRM.The configurations and operation principles of the four novel FRMs are analyzed,and the structural parameters including the number of rotor slots,split ratio,permanent magnet thickness,permanent magnet pole,stator slot opening ratio and rotor slot opening ratio are optimized.Through the comparative analysis,the performances of the four FRMs are evaluated synthetically,and both their merits and weaknesses are presented,which provides a reference for future potential applications.Finally,in order to verify the feasibility of the proposed new FRMs,the corresponding prototypes are built and tested.