Abstract
Permanent magnet (PM) machine with consequent pole (CP) rotor can improve the PM utilization ratio. However, one group PMs with the same polarity is replaced by iron core which deteriorating the electromagnetic performance of the machine, including even-order back-EMF harmonics, torque ripple, as well as unipolar leakage flux. Therefore, CP PM machine with various magnetic pole, i.e., equal pole-arc magnetic pole (EMP) and asymmetric magnetic pole (AMP) structure is proposed, with smaller torque ripple can be achieved, without deteriorating the torque ability compared with the conventional CP PM machine. Further, the influence of various CP PM magnetic pole on the end leakage flux is analyzed by three-dimensional (3-D) finite element (FE), which includes leakage flux distributions as well as magnetization of shaft. The electromagnetic characteristics of the machine with EMP and AMP rotor are compared with traditional surface-mounted and CP PM machines by FE analysis. It is demonstrated that EMP and AMP rotor structure can reduce even-order harmonics, torque ripple and end leakage flux for the machines. Finally, one prototype with CP AMP rotor is tested to confirm the theoretical and FE analysis, which includes suppression effect of even back-EMF harmonics, torque characteristics as well as leakage flux at the end shaft.
Highlights
The Permanent magnet (PM) machines can exhibit high torque density, high power density, high power factor and high efficiency owing to the employ of high magnetic energy product material, and are widely exploited in more-electric aircrafts, electric vehicles, and high-power wind generation systems [1], [2]
MACHINE TOPOLOGY WITH VARIOUS MAGNETIC POLE STRUCTURE In order to investigate the influence of various magnetic pole structures on the even back-EMF harmonics, torque ripple reduction as well as end leakage flux, the 18/20 SPM machine is employed for illustration
The electromagnetic performance of machines with various magnetic pole structure, including back-EMF, torque characteristics, unipolar end leakage flux, unbalanced magnetic force (UMF), loss and efficiency are investigated in detail
Summary
The PM machines can exhibit high torque density, high power density, high power factor and high efficiency owing to the employ of high magnetic energy product material (such as NdFeB), and are widely exploited in more-electric aircrafts, electric vehicles, and high-power wind generation systems [1], [2]. The employ of CP PM rotor results in asymmetry air-gap flux density, which lead to even-order back-EMF harmonics, higher torque ripple, serious end magnetization and unbalanced magnetic force (UMF). Multi-layer winding has been employed to suppression the even-order back-EMF harmonics, resulting complicated winding arrangement and the unipolar leakage flux has not been improved [13]. In [16]–[18], a step-staggered CP PM rotor and novel magnetic pole sequence were proposed to reduce the unipolar end leakage flux of the CP PM machine, resulting lower torque density and complicated rotor structure. The CP EMP and AMP are presented to suppression the even-order back-EMF harmonics as well as the end leakage flux.
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