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The electrical machines with fractional slot windings have been widely investigated. The main challenge of this type of machines is that the magnetomotive force (MMF) harmonics of armature winding is rich, which would lead to torque ripple, eddy current loss, and other adverse effects. In this article, multiple three-phase star–delta windings connection for multiphase electrical machine is proposed, which can efficiently reduce the MMF harmonics of armature winding. First, the general principle of harmonic elimination of multiphase electrical machine with multiple star—delta winding connection is deduced. Then, the influence of multiple star–delta windings of machines with different slot/pole combinations on MMF harmonics of armature winding is investigated. To verify the theoretical analyses, the models of permanent magnetic machine with 24-slot and 36-slot are established, and the multiple star–delta windings is compared with the conventional three-phase, star–delta windings and multiple three-phase windings in terms of torque, torque ripple, loss, vibration, and so on, so as to evaluate the superiority of this connection method. Finally, a prototype with 24-slot/10-pole is manufactured and tested. The test results verify the rationality of the theoretical analyses and simulations.

Cogging torque (CT) would cause the vibration and noise of the permanent magnet homopolar inductor machine (PMHIM), which should be suppressed. However, the unipolar air-gap flux density and the dual-segment stator and rotor cores of PMHIM make the characteristics of CT unclear, which leads to a lack of theoretical basis for suppressing the CT. Addressing this issue, the CT of PMHIM is investigated and suppressed. First, the model of CT of PMHIM with integer and fractional slot configurations is developed, and the factors affecting the CT are revealed. Then, the methods for suppressing the CT are proposed based on changing rotor parameters. The influences of different rotor parameters on electromagnetic performance, including back electromagnetic force (EMF), output torque, current, and efficiency are fully analyzed. In addition, the characteristics of the proposed method are highlighted by comparing the performance of the method proposed in this article with the global optimization method in terms of CT suppression. Finally, the theoretical analyzes are validated by experiments. The results show that the CT of PMHIM can be effectively suppressed by the proposed method in this work.

The armature winding of slotless motor is directly exposed to the air-gap magnetic field. During high-speed operation, the effective part of the armature winding cuts the flux lines directly, which would inevitably cause large ac copper loss. Moreover, when the rotor is eccentric, appreciable distortions would be appeared in the air-gap flux density. The additional flux density would aggravate the ac copper loss. In this article, the mechanism of ac copper loss of high-speed slotless motors is explained first. Then, the influence of eccentricity on ac copper loss is evaluated. Finally, the difference in the effect of dynamic and static eccentricity on ac copper loss is compared.