| Permanent magnet(PM)machines are widely applied in electric vehicles,household appliances,aerospace and various industrial applications owing to their advantages of high torque density,high efficiency and high reliability.However,high performance rare-earth PM materials are extremely expensive,resulting in high cost of conventional PM machines.Therefore,improving the utilization rate of PMs while achieving high performance is an important research topic in the field of PM machines.In response to this,all N or S poles in conventional PM machines can be replaced by iron cores to form a series of consequent-pole PM(CPM)machine,which can significantly reduce the PM consumption and improve the PM utilization rate.Therefore,various CPM machines with different structures were developed,which have received growing attention.Compared with conventional surfaced-mounted PM(SPM)machine,CPM machine has more abundant air-gap flux density harmonics and significant biased flux effect.Therefore,CPM machine is selected to be the research object of this dissertation,in which the mechanism of biased flux modulation is revealed by using theoretical analysis,finite element(FE)simulation and experimental verification on prototypes.Based on the research work,two new CPM machines with high torque density are proposed in this dissertation.The main research work and the achievements of this dissertation are as follows:(1)The background and significance of this research are introduced.The research state-of-the-art of CPM machines is comprehensively reviewed in terms of topology evolution,structure characteristics and electromagnetic performances.On this basis,the common problems of various CPM machines are summarized.(2)The MMF-permeance method is employed to contrastively analyze the air-gap permeances,PM MMFs,air-gap flux densities,back-electromotive forces(EMFs)and effective harmonic torque components of both rotor CPM and stator CPM machines,which reveals the mechanism of biased flux modulation of CPM machines.By combining stator CPM and rotor CPM structures,a typical dual-sided CPM(DS-CPM)machine is derived,of which the bidirectional field modulation effect(FME)is revealed.Moreover,the features of the torque components contributed by various working harmonics in three types of CPM machines are comprehensively analyzed and compared,and their similarities and differences in torque generation mechanism are summarized.Finally,a prototype with the conventional stator surface-inset CPM structure is designed and manufactured,and some experiments are conducted to verify the theoretical and FE analyses.(3)The air-gap FMEs in rotor surface-inset CPM machine with different key design parameters are comparatively studied with the corresponding SPM case,which reveals a fact that the modulated harmonics in CPM structure contribute a relatively higher torque component and hence exhibit a significant FME.In addition,the influences of different PM arrangements on FME in interior CPM machines are investigated,which indicates that the multi-layer PM configurations significantly weaken the FME.As a result,the multi-layer interior CPM machine can be regarded as a conventional PM machine with only one main-order harmonic contributing electromagnetic torque.A prototype with conventional rotor surface-inset CPM structure is optimally designed and manufactured,and some experiments are carried out to confirm the theoretical and FE analyses.(4)A novel switching flux stator CPM machine with U-shaped PM arrangement in stator teeth and iron bridges in stator yoke is proposed.Since the reluctance encountered by low-order working harmonics is reduced,and the torque producing ability can be effectively improved.Besides,the proposed stator CPM machine exhibits higher torque capability compared with the switching flux PM(SFPM)machines with different stator structures,which is mainly attributed to the significantly enhanced low-order working harmonics.A stator CPM prototype with the U-shaped PM structure is manufactured,and some tests are conducted.(5)A novel DS-CPM machine with stator U-shaped PM arrangement is proposed based on the biased FME.The electromagnetic characteristics of the proposed machine are analyzed and compared with a conventional DS-CPM machine with stator surfaced-inset CPM structure.It demonstrates that the proposed machine exhibits higher torque capability and larger high-efficiency operating region.Finally,a DS-CPM prototype with the U-shaped magnets is manufactured,and some experimental measurements are carried out.This dissertation has made some innovative achievements in the study of biased flux modulation mechanism of CPM machine,which lays a theoretical and technical foundation for further promoting the in-depth research and industrial application of this kind of machine. |
