In the last decade, the trend toward higher efficiency and higher torque density electrical machines (EMs) without permanent magnets (PMs) for the industrial sector has rapidly increased. This work discusses the latest research and industrial advancements in synchronous reluctance machines (SynRMs), being the emergent motor topology gaining wide acceptance by many industries. This article presents an extensive literature review covering the background and evolvement of SynRM, including the most recent developments. Nowadays, SynRM has found its niche in the EM market, and the reasons for that are highlighted in this work together with its advantages and disadvantages. The key journal publications in SynRM topics are discussed presenting the biggest challenges and the latest advancements with particular regards to the design methodology. This article aims to provide a thorough overview to the research community and industry about SynRM. There is a clear potential for SynRM to take over a significant portion of the EM market in the near future to meet efficiency standards in industrial applications without the use of rare-Earth PM technology.

The permanent-magnet (PM) machine with dual three-phase windings is proposed for applications requiring continuous operating even under a partial fault. The two windings are supplied by two separate inverters. Thus, in the event of a fault of one winding, this is disconnected, and the machine continues to be operated by means of the healthy winding. This paper investigates the PM machine with dual three-phase windings and its capabilities during faulty operating conditions. A fractional-slot interior PM machine with 12 slots and 10 poles is taken into account. Its performance is investigated according to different winding configurations. The torque behavior, overload capability, and thermal limits are evaluated under open-circuit and short-circuit faults. A finite-element analysis as well as experimental tests is carried out on a prototype of such a machine.

Fractional slot concentrated winding (FSCW) interior permanent magnet (IPM) synchronous motors are nowadays an attractive solution in automotive applications due to their advantages in terms of high performance and manufacturing simplicity. Among the different topologies, the spoke type is an effective configuration when high torque density is required. On the other hand, the motor performance are heavily related to the selected slot-pole combination. This choice is critical in demanding automotive applications, such as electric power steering (EPS) systems, where high constraints in terms of torque density, torque quality, flux weakening performance, and noise/vibration/harshness are requested. This paper deals with the design and analysis of eight optimal slot/pole combinations FSCW IPM spoke type EPS motors. Two different low cost heavy rare earths free PM typologies, ferrite and hot-pressed NdFeB, are considered. A design and optimization procedure based upon the finite element analysis is presented. The impact of the magnetic properties and the slot/pole combination on the optimal motor dimensions, torque density, and motor cost is discussed. Cogging torque, torque ripple, electromechanical performance, and the stator deformation of the machines are evaluated, and the results are compared, highlighting the advantages and the differences among the solutions.

The synchronous reluctance machines with transversally laminated rotor and multi flux-barriers per pole reach a high torque density, so that they are proposed as a valid alternative to permanent magnet machines. Such machines have been analyzed for different applications, mainly home appliance, industrial tool, traction, up to low-speed high-power generators. On the contrary, the use of synchronous reluctance machines for high-speed applications remains almost unexplored yet. The aim of this paper is to investigate the potential of a high-speed synchronous reluctance machine. An optimization is carried out to maximize the machine performance at a given speed. The machine size is fixed and the focus is on the rotor geometry, with the purpose of maximizing the electromagnetic torque, according to the necessary thickness of the ribs. It is shown that, even if the ribs are thick, it is possible to reach a proper torque density. It is shown that different solutions exist, which allow to reach high torque and minimum torque ripple. However, the optimal solutions are quite sensitive to the geometrical variations, so that a particular care is required in the manufacturing of the machine. Finally, the power limit of the synchronous reluctance motor with barrier rotor is found.

Geared devices are commonly used to match the operating speed and torque of the power source with the second-mover. Such geared devices are usually mechanical gears. As counterparts of the conventional mechanical gears, magnetic gears are becoming promising devices, mainly due to the merits of physical isolation between moving parts, no gear lubrication, no mechanical fatigue, inherent overload protection and reduced maintenance, etc. Recently, several new topologies have been proposed to achieve better performances. In this paper, a general review of magnetic gears is presented, including a discussion of the most common and upcoming topologies and a description of the working principle. A comparison of different topologies is carried out, in terms of gear ratio and torque density. The main computational techniques generally adopted for coaxial magnetic gears are listed and described. Some key aspects concerning the design, the existed challenges and potential applications are also discussed. This paper aims to provide a comprehensive overview of the magnetic gear for readers working in this field.

A criteria to design the rotor of multi flux-barrier synchronous reluctance machines is proposed. In particular, the focus will be on the proper design of flux-barriers geometry. An analytical model is adopted to compute the impact of the rotor flux-barriers on the torque, focusing on the torque ripple. Thanks to proper assumptions, the analytical model is simplified so as to highlight the main causes of torque ripple. Such an analytical model allows to derive the angles of the flux-barrier ends corresponding to the minimum torque ripple in a closed form. This result has never been presented in the past literature and it represents a useful tool as far as the motor design is concerned. Rotors with one, two and three flux-barriers per rotor pole are taken into account. However, the advantageous analytical model can be extended to any number of flux-barriers per pole. Some examples referring to 4-pole synchronous reluctance machines with different numbers of stator slots are investigated and illustrated. The results are compared with a full-featured analytical model and validated through finite element simulations.