Analysis Of Air-Gap Magnetic Field Modulation In Fault-Tolerant Flux-Switching Permanent-Magnet Machine

Fault-tolerant flux-switching permanent-magnet(PM)(FT-FSPM)machines incorporate the merits of permanent magnet synchronous machines and switched reluctance machines.FT-FSPM machines have good application prospects due to high efficiency,high reliability and good cooling conditions.In this paper,an 8/15 pole FT-FSPM machine has been taken as the research object.Based on the understanding of the structural characteristics and operating principle of the machine,the air-gap magnetic field modulation process is deeply studied.The main academic research achievements of this work are contained as follows:1.The principle of air-gap magnetic field modulation of FT-FSPM machines is briefly described by the cascade of "original magnetomotive force","salient pole reluctance" and "armature winding" called "three factor method".Moreover,the process of magnetic field modulation of the FT-FSPM machine stator and rotor salient pole modulator is analyzed by the finite element simulation.The harmonics of different orders are modulated mainly by the rotor teeth,and the stator teeth are used to assist the rotor teeth to weaken the harmonic amplitude of air-gap flux density produced by the PM magnetic field.Then,the PM magnetic field interacts with armature magnetic field to generate electromagnetic torque and complete the energy conversion.2.The air-gap flux density is deduced by the air-gap permeance model.The harmonic order and the rotation speed are obtained,which lays a theoretical foundation for the following research on the electromagnetic torque and PM eddy current loss.3.According to the interaction between the harmonics produced by the PM magnetic field and armature magnetic field,the principle of the electromagnetic torque generation and the number of effective working harmonics are determined.The mechanism of electromagnetic torque generation is analyzed by Maxwell stress tensor method.On this basis,the ratio of the torque generated by the effective working harmonics to the total average torque was analyzed by the air-gap magnetic field modulation theory.4.Based on the air-gap magnetic field modulation theory,a PM eddy current loss model is proposed,and the dominant harmonic orders of the PM eddy current loss are determined.On this basis,two new rotor structures with magnetic flux barriers are proposed to reduce the amplitude of low-order harmonics,so as to achieve the purpose of reducing the PM eddy current loss.5.The prototypes of the original machine and the new rotor structure machine are designed and manufactured.The relevant experimental platform is built in combination with the existing equipment of the laboratory.The no-load and load experiments of the prototypes verify the correctness of the theoretical analysis of the machine electromagnetic design and the principle of magnetic field modulation.In addition,the effectiveness of the new rotor structure for the suppression of the PM eddy current losses is verified by measuring the PM temperature of these two prototypes and comparing the measurement results.