Research On Novel Variable Flux Switched Flux Memory Machines

Variable flux memory machines(VFMMs)are recognized as a genuine adjustable-flux permanent magnet(PM)machines(AFPMMs).VFMMs utilize either stator armature windings or additional DC coils to energize temporary remagnetizing/demagnetizing current pulses to vary the magnetization state(MS)of low coercive force(LCF)magnets.Therefore,the flexible air-gap flux control can be achieved with negligible excitation loss.As a new concept of PM machine,VFMM is promising for many industrial applications such as automotive,wind power generation and domestic appliances,etc.Based on extensive review on the state-of-art of VFMMs,a novel topology of switched flux VFMM(SF-VFMM)is proposed to resolve the disadvantages of the existing VFMMs.The proposed SF-VFMM successfully combines the VFMM concept and SF principle,and hence inherits the energy-efficient flux regulation as well as wide speed range.Meanwhile,classic vector control can be employed for drive control due to the sinusoidal back electromotive-force(EMF).This thesis establishes comprehensive and in-depth studies on the proposed SF-VFMM in terms of its diverse topologies,electromagnetic characteristics,flux regulation mechanism,design methodology,mathematical modeling,control strategy as well as experimental test.The main research works include several aspects,which can be summarized as follows:(1)The background and significance of the research are introduced systematically,and various AFPMMs are overviewed with particular reference to their structures and control methods.Furthermore,the problems of the existing VFMM researches are highlighted.(2)Novel SF-VFMMs are presented with emphasis on several typical topologies.The structural features and operating principle are analyzed.The electromagnetic characteristics of various topologies are investigated and compared by finite-element method(FEM)in order to seek the optimal structure.(3)The flux regulation mechanism of the proposed SF-VFMMs are researched based on the solution integrated by FEM and analytical hysteresis models formulated by piecewise linear approximation as well as Frolich functions,respectively.The on-load demagnetization phenomenon of LCF PMs in hybrid PM SF-VFMM is unveiled and studied,and the basic design considerations for preventing this kind of demagnetization are provided.(4)Based on magnetic circuit modeling,the analytical expressions of key electromagnetic parameters of SF-VFMMs are derived,which disclose the constraint relationship between various parameters.The design principle for magnetic circuit patterns of hybrid PM SF-VFMM is investigated.Finally,a generic design methodology of SF-VFMM is summarized and introduced.(5)The "winding function switching" concept for magnetizing windings is introduced.Based on this concept,"hybrid excitation" and "DC-to-AC switching" SF-VFMMs are proposed,respectively.The influences of "hybrid excitation" operation on the electromagnetic characteristics of the proposed machines are evaluated,which aid the optimal implementation of the control strategy for DC field excitation.The feasibility of "DC-to-AC switching" of the magnetizing coils is discussed,and the impact of this "winding function switching" on the flux-weakening performance is investigated.(5)The nonlinear mathematical model of the proposed SF-VFMM is built,and the simulation of the drive control system is conducted based on MATLAB/Simulink platform.A stepwise magnetization based control strategy for the SF-VFMM is proposed according to the variation of the operating characteristics at different magnetization states.Besides,the effectiveness of the control strategy is both simulated and experimentally validated.(6)The selected proof-of-principle prototypes are fabricated.The test bench for dynamic and static performance as well as magnetization control is built.The experiment tests on the main electromagnetic characteristics,open-circuit and on-load magnetization control of the prototype are carried out.The research works established in this thesis lay a theoretical and technical foundation for the further study and industrialization of the proposed SF-VFMM.