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In this study, the electromagnetic performances of dual 3‐phase permanent magnet (PM) machines with coil span of two slot‐pitches are comparatively investigated. It mainly focuses on two PM machines with different slot/pole number combinations (Ns/2p), that is, the 24‐slot/10‐pole and 24‐slot/14‐pole machines (2p = Ns/2 ± 2). First, winding configurations are illustrated for these two dual 3‐phase machines with 30° angle displacement. Then, the winding factor, back electromotive force, average torque, torque ripple, iron and PM losses, short‐circuit (SC) current, and PM irreversible demagnetisation are analysed and compared for both machines on the conditions of healthy operation and one set of three‐phase fault, that is, SC or open circuit (OC), respectively. The comparative results show that on healthy condition the 14‐pole PM machine has a slightly larger torque output. Besides, on 3‐phase OC condition, the 14‐pole machine also performs better over‐rating torque capability. In terms of iron and PM losses, the 10‐pole machine has smaller iron losses but larger PM losses than the 14‐pole machine. Moreover, on 3‐phase SC condition, the 14‐pole machine has a significantly lower risk of PM irreversible demagnetisation than the 10‐pole machine, although both machines have very similar SC currents. Finally, the 24‐slot/10‐ and 14‐pole dual 3‐phase PM machines are both prototyped and some tests are carried out for validation. [ABSTRACT FROM AUTHOR]

A hybrid analytical and lumped-parameter thermal model is proposed in this paper to estimate the transient and steady-state two- and three-dimensional (2/3-D) spatial magnet temperature distributions for an interior permanent magnet synchronous machine (IPMSM). On the basis of a lumped-parameter thermal model (LPTM), the magnet analytical thermal models (ATMs) are synergized to establish the hybrid thermal model. By utilizing the transient or steady-state boundary conditions calculated by the LPTM, the ATMs are obtained by solving the heat conduction equations to estimate the spatial magnet temperature distributions in the 2-D horizontal-vertical and axial-vertical planes, which can also be extended to the 3-D temperature distribution by utilizing the multi-slice method. Meanwhile, the non-uniform magnet eddy current loss is also considered. Finally, both electromagnetic-thermal coupled finite element analysis method and experiments are used for verification based on a totally enclosed IPMSM. [ABSTRACT FROM AUTHOR]

Lumped-parameter thermal models (LPTMs) have been widely used to estimate critical temperatures in permanent magnet synchronous machines (PMSMs). However, in some cases, they may be incapable of predicting the hotspots and even cause temperature misestimation. In this paper, the synergized lumped-parameter and sub-domain thermal models are proposed for surface-mounted PMSMs to track the hotspots in the most vulnerable components, i.e., active/end-windings and rotor magnet. Firstly, the “T-type” elementary network based LPTM is developed to predict the average temperatures in main components and the boundary conditions. Secondly, the boundary conditions are applied to three sub-domain thermal models for the active/end-windings and the rotor magnet to predict the respective hotspots and to further correct the misestimated average temperatures. Finally, the proposed synergized thermal model is verified by the experiments on a prototype surface-mounted PMSM under various load conditions. [ABSTRACT FROM AUTHOR]

In this article, a simplified three-dimensional (3-D) hybrid analytical thermal model for surface-mounted permanent magnet (PM) synchronous machines is proposed and applied to investigate the influence of PM segmenting strategies on the spatial PM temperature distributions and hotspots. The developed 3-D hybrid thermal model synergies the lumped-parameter thermal model and analytical method and is able to estimate 3-D spatial temperature distributions and hotspots for both unsegmented and segmented surface-mounted PMs accounting for the uneven PM eddy current loss distributions. Meanwhile, by utilizing the proposed matrix-based post-processing methods, the developed hybrid analytical thermal model has a simple mathematical expression but persists in high estimation accuracy. Finally, the proposed hybrid analytical modelling method is validated by 3-D electromagnetic-thermal coupled FEA and experiments. [ABSTRACT FROM AUTHOR]

In this article, the rotor stress is analysed for a high-speed permanent magnet (PM) machine (HSPMM) with segmented magnets retained by a carbon-fibre sleeve. The influence of rotor PM segmentation is firstly considered in the stress analysis. It is found that when the segmented magnets are under tensile stress, significant sleeve stress concentration will occur due to magnet edging effect. By contrast, the PMs will benefit from the segmentation with reduced tangential stress. This stress reduction effect is enhanced when the number of PM segments is larger. Furthermore, the influence of PM segmentation on the worst operating scenario is determined. In order to avoid stress concentration due to PM segmentation, the design guidelines are then given by investigating the influence of sleeve thickness and interference fit. A new design scheme of sleeve thickness is proposed based on the identified worst case scenarios. Finally, a 6-slot 4-pole high speed PM machine with segmented magnets retained by carbon-fibre sleeve is prototyped and tested at the speed of 90 krpm. The rotor stability indirectly indicts the validity of the theoretical analysis and design scheme. [ABSTRACT FROM AUTHOR]

Current harmonics are ubiquitous in dual three phase (DTP) permanent magnet synchronous machine (PMSM) drives. Due to back electromotive force (EMF) distortion, significant current harmonics are generated in the DTP-PMSM system. The influence of back EMF harmonics is investigated in this paper and a novel switching-table-based direct torque control method to compensate the selected current harmonics caused by the back EMF harmonics is proposed. It shows that by employing different optimal action time durations for voltage vectors in the z1z2 subspace and setting the synthetic voltage vectors to non-zero, the stator flux harmonics caused by the back EMF harmonics can be selectively compensated, as verified by experiments. [ABSTRACT FROM AUTHOR]

The lumped-parameter thermal network (LPTN) has been widely used in the thermal analysis for electrical machines. Nevertheless, since the thermal resistances are defined based on the one-dimensional (1-D) heat transfer equation, it will cause the misestimation of the average temperatures when the thermal model extends to two dimensions or three dimensions. In this article, a hybrid thermal model utilizing the synergies of LPTN and 2-D analytical thermal models is developed to address this issue and to predict accurate critical temperatures, especially the average and maximum temperatures of the active and end windings. The 2-D analytical thermal models are obtained by solving the Poisson's equations with the Dirichlet boundary conditions extracted from the LPTN. The derived analytical solutions are expressed as the Fourier series, which can be further simplified by utilizing the first term only to represent average and maximum temperatures with sufficient accuracy and short computation time. The hybrid thermal model is applied to a totally enclosed forced convection permanent magnet synchronous machine and validated by numerical techniques and experiments. [ABSTRACT FROM AUTHOR]

Fractional-slot permanent magnet (PM) machines with an odd number of stator slots are attractive candidates for industrial applications due to their high torque density and low torque ripple. However, the unbalanced magnetic force is detrimental to the bearing and yields noise and vibration. This paper determines the existence criterion of UMF on both open-circuit and on-load conditions by analysis of air gap field and magnetic force waves. Only when the machine periodicity is one, will the open-circuit UMF be generated due to the mutual interaction between the modulated PM harmonics and the original PM harmonics. In addition, the existence of on-load UMF in machines with a periodicity of one is confirmed even when the slotting effect is ignored. Furthermore, among the five investigated machines with a given odd slot number of 9 but different pole numbers, the UMF in a machine with two poles is the smallest since the magnitude of the 2nd harmonic in the armature reaction is the smallest compared with other contributing harmonics. Meanwhile, the UMF in a machine with pole number 2p = Ns−1 is the largest due to the relatively larger magnitude of the (p + 1)th armature reaction harmonic and the additive effect between the first order radial and tangential stresses. [ABSTRACT FROM AUTHOR]