Abstract
This paper aims to present a general and effective analytical approach to calculate the air gap flux density and the back electromotive force (EMF) of a flux-switching permanent magnet (FSPM) machine. The proposed analytical expression of the air gap flux density is based on an improved air gap permeance function considering the geometries of slotted stator core pieces and magnets between stator teeth as well as the salient rotor poles. The back EMF equation is accurately derived using the proposed air gap flux density equation expressed in terms of practical machine dimensions and thus it provides the key design factors as well as details of the back EMF production mechanism. To validate the proposed analytical expressions, they are applied to the case study of a 12-slot 10-pole FSPM machine, and the finite element analysis results confirm the analytical predictions. Besides, for the proposed analytical model, the effects of the machine’s geometries on back EMF characteristics are investigated. The investigation shows that the ratio of rotor slot opening to slot pitch has a significant effect on the back EMF, and its optimal value is suggested. The proposed equations also provide a mean to choose the slot and pole combinations to obtain a higher power density.
Highlights
The investigation shows that the ratio of rotor slot opening to slot pitch has a significant effect on the back electromotive force (EMF), and its optimal value is suggested
A flux-switching permanent magnet (FSPM) machine has a different structure and uses a different operating principle compared to conventional PM machines
An FSPM machine with modular and segmented rotor was described in references [6,7], which showed that the modular rotor significantly reduced iron losses
Summary
A flux-switching permanent magnet (FSPM) machine has a different structure and uses a different operating principle compared to conventional PM machines. For the analysis of such an FSPM motor, in reference [13], the air gap flux densities were obtained by expressing the uneven air gap with various lumped magnetic reluctance networks. The precise equations of the air gap magnetic flux density and the back EMF expressed in terms of the actual machine geometries are derived. Using the proposed air gap permeance and the magnetomotive force (MMF) of the air gap calculated from the equivalent magnetic circuit, the magnetic flux density equation is derived and leads to the back EMF equation Both equations are used to analyze the characteristics of FSPM motors with geometry variations. The validity of the analytical results obtained from the proposed characteristic equations is confirmed by comparing them with the finite element (FE) analysis results
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