Abstract
Due to their particular structure, switched-flux permanent magnet machines have become a very interesting alternative for many applications. This is why some recent studies have been focused in the understanding of the operating mechanism of these machines via the MMF-permeance modelling. However, the models that can be found in the literature make some simplifications that reduce their accuracy when predicting the performance of switched-flux machines. For example, the models that can be found in the literature are commonly not precise enough for machines with a wide slot, because the influence of the modulator of the primary side of the machine is neglected. In this article, a precise analytical model is developed for a 6/13 C-Core switched-flux machine via a combination of a magnetic equivalent circuit and a MMF-permeance model. The model is based on the magnetic field modulation principle. The analytical model is used to explain the flux focusing effect and the force generation mechanism of switched-flux machines. A new concept of PM field harmonic efficiency ratio is used to identify the most efficient PM field harmonics of 2 switched-flux machines. The precision of the model is validated via 2D and 3D Finite Element Method simulations, and experimental measurements that were obtained with a linear machine prototype. The results show that the model can predict the performance of switched-flux machines with a high accuracy level.
Highlights
Switched-Flux Permanent Magnet Machines (SFPMs) are a kind of Permanent Magnet (PM) machine that has both the armature winding and the PMs mounted in the primary side, while the secondary is composed of a salient ferromagnetic structure
As the PMs and the armature are placed in the same side, the active elements can be cooled in SFPMs [1]
Conventional PM machines need to place either the armature winding or the PMs along the whole stationary rail. Thanks to their passive ferromagnetic secondary, Linear Switched-Flux Permanent Magnet Machines (LSFPMs) exhibit a much lower cost when compared to conventional PM machines in long stroke applications [5]
Summary
Switched-Flux Permanent Magnet Machines (SFPMs) are a kind of Permanent Magnet (PM) machine that has both the armature winding and the PMs mounted in the primary side, while the secondary is composed of a salient ferromagnetic structure. The slotting of the primary and the secondary generates a distortion in the distribution of the airgap flux density This distortion can be explained via the magnetic field modulation theory [21]. This time, the distorting effect of the primary modulator is so significant, that the dominant harmonic is changed. Qualifying this distorting effect as negligible would be incorrect This effect is a crucial part in the operation of large slot-opening SFPMs. the waveform of the airgap flux density that is produced by the magnets in the totally slotted machine from Fig. 2 is given, and can be obtained from (x, t). The bias of the turns function for the example machine, T0, is given by
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