This paper overviews high-speed permanent magnet (HSPM) machines, accounting for stator structures, winding configurations, rotor constructions, and parasitic effects. Firstly, single-phase and three-phase PM machines are introduced for high-speed applications. Secondly, for three-phase HSPM machines, applications, advantages, and disadvantages of slotted/slotless stator structures, non-overlapping/overlapping winding configurations, different rotor constructions, i.e., interior PM (IPM), surface-mounted PM (SPM), and solid PM, are summarised in detail. Thirdly, parasitic effects due to high-speed operation are presented, including various loss components, rotor dynamic and vibration, and thermal aspects. Overall, three-phase PM machines have no self-starting issues, and exhibit high power density, high efficiency, high critical speed, together with low vibration and noise, which make them a preferred choice for high-performance, high-speed applications.

This paper investigates the influence of static and dynamic rotor eccentricities on electromagnetic performance, including air-gap flux density, back electromotive force (EMF), electromagnetic torque, cogging torque, and unbalanced magnetic force (UMF), of a 2-pole/3-slot permanent magnet (PM) motor considering eccentricity ratio, eccentricity angle, and rotor initial angle. Both finite element analyses and experiments show that in a 2-pole/3-slot PM motor, the static rotor eccentricity leads to unbalanced magnitudes and phase angles of fundamental back-EMFs of three phases but does not change the harmonic contents, while the dynamic rotor eccentricity will not cause unbalance in three phase back-EMFs but affects the harmonic contents of back-EMFs and their phase angles, which causes asymmetric positive and negative half-periods and corresponding even harmonics of phase back-EMF waveform. In addition, both static and dynamic rotor eccentricities have negligible influence on the average torque, but result in large torque ripple, cogging torque, and UMF.

In this paper, three 6-slot/2-pole high-speed PM motors with 1, 2, and 3 coil-pitch windings are optimized by the finite element method taking into account of stator copper loss and iron loss. Their electromagnetic performances are analyzed and compared, including air-gap flux density, back electromagnetic force, electromagnetic torque, winding inductances, and various loss components. For high-speed application, compared with 1 and 3 coil-pitch windings, the proposed 2 coil-pitch windings have a good trade-off between winding factor and end-winding axial length which are attractive for improved torque density. Finally, the experimental results are given to validate some of the finite element predicted results.

This paper investigates the influence of stator slot number on electromagnetic performance of 2-pole high speed permanent magnet (HSPM) slotted motors with toroidal windings. Four 2-pole slotted motors with different slot numbers, i.e. 3, 6, 9, and 12, are globally optimised for maximum torque, and their electromagnetic performance are compared, including winding factor, air-gap flux density, back-EMF, cogging torque, electromagnetic torque, winding inductances, unbalanced magnetic force (UMF), and various loss components. It shows that the 6-slot/2-pole HSPM motor with toroidal windings is eminently suitable for high speed application due to no UMF and easy to realise a modular structure. In addition, toroidal and tooth-coil windings are compared in the 3-slot/2-pole motors, and the results confirm that toroidal windings are not suitable for use in the 3-slot/2-pole HSPM slotted motor due to large airgap field harmonics. Finally, a 6-slot/2-pole prototype motor is manufactured and tested to validate the finite element (FE) predictions.

This paper proposes an analytical multi-element thermal modelling method for predicting the sleeve and magnet thermal fields for high-speed permanent magnet machines (HSPMMs). The analytical model is developed based on the conduction heat equations and the continuity equations of heat transfer. The rotor temperature distributions and hotspots can be accurately predicted with the aid of the boundary conditions from a lumped-parameter thermal model. The proposed method is applied to investigate the influences of different PM segmentations and rotor sleeve materials on the rotor thermal performance. Based on a 3-slot/2-pole HSPMM, it is shown that the PM segmentation parallel to the magnetisation direction together with the carbon fibre sleeve can significantly ease the rotor thermal stress. The finite element analyses and experiments have been used for validation.

In this paper, a high-speed permanent magnet (HSPM) motor having 6-slot/2-pole (6s/2p) number combination and 2 coil-pitch windings are developed for domestic appliance application. Two HSPM motors with different layouts of 2 coil-pitch windings are optimized and their electromagnetic performances are evaluated. The best winding configuration is then identified for shorter motor axial length and larger torque density. Since 3-slot/2-pole (3s/2p) HSPM motors with non-overlapping windings have the same winding factor, a comparison between 3-slot and 6-slot motors is also conducted, particularly for torque density, losses, and unbalanced magnetic force (UMF). It shows that 6s/2p PM motors with 2 coil-pitch windings are suitable for high-speed application without UMF and less rotor PM loss. Finite element predicted electromagnetic performances are validated by experiments made on two prototype motors.