Research On Design Methodology And Optimization Techniques Of Novel Hybrid-magnetic-circuit Variable Flux Memory Machines

Permanent magnet(PM)machines have become the mainstream machine for new energy vehicle drives.Although the conventional PM machines can achieve flux weakening by applying demagnetizing currents to extend their speed range,they still suffer from a limited speed range and a significant reduced efficiency in the high-speed operating region.Variable flux memory machine(VFMM)arises at the historic moment,which is considered as a truly global high-efficiency machine.The magnetization states(MSs)of the employed low coercive force(LCF)PMs can be flexibly adjusted by transient current pulses,bringing the benefits of high torque density,wide operating range,and high efficiency in the overall region,so that VFMM has a broad application prospect in the field of electric vehicles.This dissertation focuses on the topological construction design method and multi-operation optimization technology of VFMM,successively proposing two novel hybrid magnetic circuit VFMMs(HMC-VFMMs).The main research work and achievements of this dissertation include:1)A construction theory and a design method of VFMM topology are proposed based on the basic unit method.The equivalent magnetic circuit model and finite element(FE)method are used to analyze and compare existing VFMM topologies and summarize their differences in the key electromagnetic characteristics.To address the issues of the existing HMC-VFMM,the series and parallel magnetic circuits of this kind of machine are separated using the proposed topological construction method,thereby deducing symmetric and asymmetric separated magnetic circuit HMC-VFMM.Besides,the superiorities of the proposed machines in electromagnetic performance are further confirmed by analyzing the magnetic circuit models.2)An efficient optimization method considering multiple MSs and operation conditions is proposed to improve the operation efficiency of VFMM.This method includes two rounds of optimization,i.e.,dual-operating-mode rough optimization(DOM-RO)and multiple-operating-mode elaborate optimization(MOM-EO),which can achieve a rapid reduction of the parameter optimization range and an effective improvement of the overall efficiency over a wide operation condition,respectively.Furthermore,a novel multi-period field circuit coupling analysis model considering multiple MS in a single calculation case is established to achieve fast optimization of machines.3)A novel symmetric separated magnetic circuit HMC-VFMM is proposed,which is globally optimized by utilizing the proposed optimization method.Besides,the electromagnetic characteristics of the proposed machine are analyzed by the FE method as well as compared with those of two HMC-VFMMs with different extreme PM ratios.Finally,a symmetric separated magnetic circuit HMC-VFMM prototype is fabricated and relevant experiments are conducted to verify the feasibility of the proposed design.4)A novel asymmetric separated magnetic circuit HMC-VFMM is proposed,whose magnetic circuit model is established and analytically analyzed to elucidate the intrinsic mechanism for the expansion of its flux regulation range,as well as to reveal the magnet axis shifting(MAS)effect of the proposed asymmetric rotor design and the influence of this effect on the electromagnetic characteristics.A three-stage optimization method considering the MAS effect is proposed to improve the torque performance of the machine.The electromagnetic characteristics of the machine optimized by two different optimization methods are comprehensively evaluated and compared by the FE method to confirm the effectiveness of the three-stage optimization method.Finally,an asymmetric separated magnetic circuit HMC-VFMM prototype is fabricated and relevant experiments are conducted to verify the feasibility of the design.5)For electric vehicle applications,the global optimizations of three HMC-VFMMs with the proposed asymmetric,symmetric separated magnetic circuit,and existing integrated magnetic circuit respectively are implemented by the FE method.Besides,the electromagnetic characteristics of these three structures are comprehensively compared and analyzed to achieve the topological selection of high-power VFMM.A 30 k W VFMM engineering prototype for electric vehicles is developed,and the differences and relationships between the low-and high-power prototypes are summarized.Finally,relevant experimental tests are conducted on the30 k W prototype to confirm the superiority of the proposed VFMM in terms of overall efficiency improvement.This dissertation is devoted to an in-depth research of the novel topology,design methods and optimization techniques of HMC-VFMMs,thereby providing some theoretical and technical support to further promoting the engineering application of VFMMs.