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This article investigates the influence of manufacturing tolerances of modular stator core, including radial, circumferential, and axial displacements, on the electromagnetic performance of a modular permanent magnet (PM) machine. First, the analytical analysis of no-load back electromotive force (EMF), circulating current, cogging torque, and unbalanced magnetic force (UMF) is derived. Second, several typical cases are selected to investigate the effects of the three displacement faults. Then, the effects of a single module under the same displacement amplitude fault are compared, and the results reveal the tolerance of electromagnetic performance to different displacements. Finally, references for the design, processing, and manufacturing of modular motors are provided by the analysis results of this article.

In high-temperature superconducting homopolar inductor machine (HTS-HIM), the stationary high-temperature superconducting (HTS) excitation coil is directly exposed to complex external perpendicular alternating field (EPAF). In this situation, the ac loss including dynamic loss and magnetization loss will occur in the HTS coil carrying direct current, which is harmful to the operation of HTS-HIM. To avoid the thermal runaway quench of HTS coil caused by ac loss and ensure the safe and reliable operation of HTS-HIM, the EPAF acting on the HTS coil is investigated and suppressed in this article. First, the characteristics of the EPAF of HTS coil in HTS-HIM are obtained through theoretical and finite element analysis. Then, based on the distribution of EPAF and the special structure of HTS-HIM, a combined suppression method using two sets of U-shaped armature windings and L-shaped flux diverter is proposed and analyzed. The results show that the shielding factors of fundamental and dc components can be reduced to 25% and 31%, respectively.

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.

A method for calculating the critical current of high temperature superconducting (HTS) machine using boundary magnetic vector potential constrain and bisection method is proposed in this article. The indirect coupling between superconducting and non-superconducting regions of HTS machine is realized through boundary magnetic vector potential constrain, which avoids the model complexity caused by direct coupling and saves computation time. Taking a 10 kW double-stator HTS machine (DS-HTSM) as an example, the process of calculating critical current through proposed method is given. To verify the correctness and accuracy of proposed method, a direct coupling model of DS-HTSM is established. The results show that there is a high consistency of critical current and magnetic field distribution of direct and indirect coupling models. The calculated results of critical current are in agreement with the experimental in relevant research. The proposed method is quite effective for calculating the critical current of different HTS machines.