Abstract
This paper investigates the local permanent magnet (PM) demagnetization characteristics of stator-PM flux-switching (SPM-FS) machine and rotor-PM flux-switching (RPM-FS) machine. The partial demagnetization mechanisms of two machines are analyzed based on a simple magnetic circuit method, and verified by finite-element analysis (FEA). In addition, the performance degradation due to demagnetization effect is evaluated, and a comprehensive comparison of a pair of three-phase prototyped machines is conducted, where the two machines have the same stator outer diameter, stack length and rated current density. The predicted results indicate the demagnetization is generated in the corner parts of PMs near to air-gap for SPM-FS machines, and then the torque performances are degraded, while PMs in RPM-FS machine are hardly influenced by demagnetization effect. Hence, the anti-demagnetization capability of the RPM-FS machine is significantly stronger than that of the SPM-FS machine.
Highlights
The stator-permanent magnet (PM) flux-switching machines (SPM-FS), exhibiting the benefits of high power density and improved reliability, have attracted considerable attentions.[1]
It can be found that the working point of each magnet element in the rotor-PM flux-switching (RPM-FS) machine is greater than 0.86T, which is significantly higher than that of the stator-PM flux-switching machines (SPM-FS) machine, and the risk of demagnetization can be decreased significantly
For the RPM-FS machine, both the PM flux and rated torque waveforms under demagnetized and ideal conditions are almost coincided at T PM = 100 ◦C and 140 ◦C, since the working points of the PMs are all greater than Bknee at TPM = 100 ◦C and 140 ◦C, as verified by Fig. 2(g), where all the elements in the magnets are under safe status
Summary
The stator-PM flux-switching machines (SPM-FS), exhibiting the benefits of high power density and improved reliability, have attracted considerable attentions.[1]. It worth noting that the armature slot areas are significantly reduced due to the co-existence of PMs and armature windings in stator, which results in a degraded torque density.[2] In addition, since the PMs are wound around by the concentrated windings, the winding heat transfers to the PMs directly resulting in a decreased PM remanence Br (T) and an increased PM knee point Bknee (T), and the irreversible demagnetization may be generated.[3]. The prototypes of a pair of SPM-FS and RPM-FS machines are manufactured and measured to verify the theoretical analysis and FEA predicted results
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