This paper presents a novel parametrization for the flux barrier profiles of synchronous reluctance and permanent magnet assisted reluctance machines. In literature there are several methods used to design rotor flux barriers of various types, however the vast majority use only a few parameters to characterize their shape. These approaches are proven to be effective in terms of simplicity and computational burden required to achieve an optimal design. However, simplified parametrizations certainly decrease the degrees of freedom when designing the whole barrier shape. In this paper, an attempt to increase the degrees of freedom, introducing a novel rotor flux barrier parametrization, is presented. The method proposed uses natural splines, defined by the positions of a set of control points, to form the shape of the flux barriers. The spline and state-of-the-art barrier profiles are compared from both electromagnetic and mechanical perspectives. The results of this investigation show that by increasing the degrees of freedom it is possible to obtain better performance characteristics. The proposed parametrization is applied to a 6-pole synchronous reluctance motor and its permanent magnet assisted variant, optimized for a traction application. A prototype has been manufactured and tested to experimentally validate the design methodology.

Synchronous reluctance (SynRel) machines are considered one of the promising and cost-effective solutions to many industrial and mobility applications. Nonetheless, achieving an optimal design is challenging due to the complex correlation between geometry and magnetic characteristics. In order to expand the limits formed by template-based geometries, this work approaches the problem by using topology optimization (TO) through the density method (DM). Optimization settings and their effects on results, both in terms of performance and computation time, are studied extensively by performing optimizations on the rotor of a benchmark SynRel machine. In addition, DM-based TO is applied to an existing rotor geometry to assess its use and performance as a design refinement tool. The findings are presented, highlighting several insights into how to apply TO to SynRel machine design and its limitations, boundaries for performance improvements and related computational cost.

This paper presents a systematic comparative design study of permanent magnet assisted synchronous reluctance (PMaSyR) machines for a light traction application aimed at considering an holistic approach for a given outer envelope and cooling system specification. Electromagnetic, structural and thermal aspects are all accurately considered in a computationally efficient manner using a hybrid analytical-finite element (FE) design approach. The SyR machine geometries providing the maximum torque with increasing number of poles are identified and their performance deeply investigated with full FE analysis. The study has been carried out considering several requirements in terms of base and maximum speeds with the aim of drawing general design considerations. Results reveal that the optimal pole number from a torque perspective depends on the considered maximum speed. The reasons behind this behavior are fully investigated as well as how and why the optimal geometries change. The optimal SyR machines are then compared also considering the insertion of permanent magnets within the rotor slots with the aim of maximizing the constant power speed range. The rationales behind the selection of the machine to manufacture are then outlined including aspects related to efficiency and demagnetization under the worst short circuit condition in the entire torque-speed range. The optimized machine (after a FE-based design refinement) has been manufactured and tested on an instrumented test bench validating the proposed design approach and the deduced design insights.

Powder Bed Fusion - Laser Beam (PBF-LB), a form of additive manufacturing (AM) for Nd-Fe-B permanent magnets, is attracting substantial interest for its ability to process functional magnetic materials while capitalizing on AM's design flexibility and waste reduction. As the demand for rare-earth magnets declines due to scarcity and high costs, AM emerges as a pivotal player in the future of electrical machines. However, crack formation and delamination during laser-based AM hinder the production of hard magnetic Nd-Fe-B components, compromising part integrity. This paper addresses these challenges by successfully controlling laser scan strategies and presenting an approach to minimize delamination. Resin infiltration is explored as a potential solution to mitigate residual cracking. Optimized scan strategies and resin infiltration enhance the structural integrity of printed magnets, meeting specific application requirements. As a vessel to investigate the proposed approach for the AM of Nd-Fe-B magnets, a Permanent Magnet assisted Synchronous Reluctance motor has been designed using a particular shape of permanent magnets enabled by the AM. Experimental results align with the FE findings, showcasing a 12% increase in average torque using PBF-LB-produced permanent magnets. This indicates that AM's enhanced design freedom, unconventional shapes, and minimal post-processing contribute to improved reliability, efficiency, and overall performance.

This paper proposes a highly accurate and computationally efficient distributed magnetic equivalent circuit (DMEC) model for synchronous electric machines. The model - based on a two directional flux paths cell element - is derived in a general fashion in order to easily define different geometries. All the steps required for the DMEC definition and its non-linear resolution are detailed including the rationals behind the geometrical discretization, the setting of the excitations and the boundary conditions implementation. A comprehensive comparison between results obtained using DMEC and FEM is provided for three different machine types, namely surface permanent magnet (SPM) machine, permanent magnet synchronous reluctance machine (PMaSynRel) and a synchronous reluctance (SynRel) machine in a wide range of operation points. The computational advantage of proposed model is also investigated as function of the level of discretization and so accuracy of the estimated performance. The predictions of the proposed DMEC model are fully experimentally validated with an extensive test campaign on an off-the-shelf synchronous reluctance motor.

The drivetrains of large transportation systems, such as aircraft or ships, are evolving toward hybrid configurations with dc primary power distribution thanks to their higher efficiency. In this context, synchronous homopolar machines (SHMs) equipped with diode rectifiers are promising solutions for onboard generation units as they eliminate the need for active power electronic converters. In this article, a synchronous homopolar generator with a dual dc-link configuration, where each power bus is supplied via two series-connected rectifiers, is designed and tested. A direct oil-cooled excitation coil provides the full voltage-control capability of the two independent dc-links. The manuscript addresses the challenge of the analytical electromagnetic sizing of this machine topology, which has an intrinsic 3-D magnetic behavior. The electromagnetic design is validated through a 3-D-FE analysis, while the thermal sizing of the solenoid hollow oil-cooled excitation coil is analytically carried out and validated through CFD analysis. A 1.2-kW, 6000-rpm proof-of-concept demonstrator has been built and tested, and the reported measurements match the predicted electromagnetic and thermal operation. Although the experimental validation is performed on a small-scale prototype, this work may provide a foundation for designing an active power electronic-free electric generation unit for future large transportation systems.