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Fractional-slot windings, widely applied in multiphase electric machines, can further reduce cogging torque. However, concerns arise from the adverse effects of space harmonics introduced by the rich armature winding magnetomotive force (MMF). To reduce the space harmonics of armature winding MMF, a Two-terminal Hybrid Connection Method (TTHCM) of fractional slot electrical machine is proposed. Firstly, the general principle of harmonic elimination is derived, outlining the specific armature MMF harmonic orders that TTHCM can eliminate under different pole-slot combinations. Taking the example of a machine with 24-slot/10-pole configuration, the analysis process is presented. And the harmonic orders eliminated include the 1st, 7th, 11th, 13th, 17th, 23rd, and 25th space harmonics of the armature MMF. Next, models for a conventional three-phase machine, star-delta, dual three-phase, and TTHCM are established and compared. It is demonstrated that, compared to the dual three-phase connection, the TTHCM can enhance the torque, reduce torque ripple, decrease permanent magnet eddy current loss, and improve vibration performance without increasing the complexity of the control system. Finally, a prototype of TTHCM machine is manufactured and tested. The reliability of the theoretical and simulation analyses is confirmed.

The electric aircraft propulsion system requires high speed and high power-weight ratio electrical machines. This paper presents a superconducting homopolar inductor machine (HIM) based on HTS REBCO magnets, which could be a promising candidate for high power density electrical machines for future electric aircraft propulsion system. The HTS-HIM has a simple structure, high rotating speed, and huge potential to achieve a high power-weight ratio (kW/kg). This paper presents our design of a 10 kW HTS-HIM with a rotating speed of 3000 rpm. The structure and crucial parameters of HTS-HIM are presented. A 2D-axial pancake coil model for HTS REBCO magnets was built by using COMSOL. Based on this model, HTS REBCO magnets were design and optimized. The loss of REBCO magnets was also calculated. Finally, the output performance of the 10 kW HTS-HIM was simulated. Our work provides preliminary simulation and analysis for future MW-class HTS-HIM.

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.