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.

Synchronous reluctance machines are becoming a widespread solution in many engineering areas thanks to their simple rotor structure, the absence of rare-earth permanent magnets and high efficiency. The design of such machines is a widely investigated research topic, given the challenge of analytically estimating their electromagnetic performance, especially when a high-speed scenario is considered. The design choices and assumptions, which include the selection of the magnetic load and the stator and rotor lamination materials, play an important role in the machine performance. Consequently, it is of paramount importance to assess their validity. This paper, after a brief re-call of a general design methodology able to consider all the magnetic non-linearities and structural and thermal limitations occurring at high-speed, presents a sensitivity analysis against the magnetic load when a Cobalt-based alloy is adopted for both stator and rotor laminations. The analysis is carried out for different speeds up to 90 krpm, in order to draw general design guidelines for a given outer envelope and cooling system.

This work discusses the modelling approach adopted for the estimation of the voltage distribution within hairpin windings of electrical machines. The physical phenomena and the major contributors to the occurrence of the uneven voltage distribution are first described. Then, the equivalent circuit used to predict the voltage distribution is presented in detail. The circuital parameters employed in the equivalent circuit are estimated via finite element electrostatic and electromagnetic analyses. Finally, a numerical tool is used to solve the differential equations describing the equivalent circuit above mentioned. Simulation results are illustrated and discussed. The phenomena under investigation are applied to a pre-defined reference system, consisting of slot motorettes.

Synchronous reluctance machines (SynRel) are becoming very attractive for different applications because of their reluctance nature, easy manufacturability and low cost. Their design still represents a challange because of the many degrees of freedom that their rotor structure presents. Furthermore, in order to obtain a design with defined electromagnetic characteristics and low torque ripple machine geometry is needed to be optimised. In this paper, three different optimisations are performed on 6 poles SynRel motor with three flux barriers per pole. The aim of the work is to show the effect of the objective selection on the optimization process. An automatic procedure has been applied coupling finite element analysis with an optimization algorithm that is working towards the competitive targets of maximazing the torque, while minimizing the torque ripple and losses. The effects of these objectives on the geometrical variables are investigated in detail. The outcome of the analysis show how the problem definition heavily affects the obtained results. This gives useful insights on how to approach SynRel rotor design.

This paper presents a comparison between hairpin and random distributed winding in electrical machines for automotive applications. Indeed, the overall performance of an electrical drive system is seriously affected by its winding design. The considered electrical machine has a peak power of 115kW and a maximum operating speed of 12000 rpm. Both cost and manufacturing aspects are here discussed in detail. Two different machine topologies have been investigated and Finite Element Analysis (FEA) results are presented and discussed. Then, the comparison between hairpin and random winding configuration in terms of AC copper losses are presented for the selected geometry. The accurate AC losses estimation can be done by modelling each single conductor. In order to significantly reduce the simulation time, a domain model reduction has been adopted. Based on two different driving cycles, Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET), the AC losses have been evaluated. It is shown that horizontal pin segmentation can contribute to considerable AC loss reduction.

Nowadays, Interior Permanent Magnet Synchronous Machines (IPMSM) are widely adopted in various sectors such as automotive, railway or public transportation (e- buses, trams, etc.). Among the benefits that these machines present, they offer a number of design degrees of freedom. Furthermore, they can operate over a wide speed range, with a good flux weakening capability. One of the main challenges is to define a complete geometrical parametrization, in order to identify an optimal structure that satisfies the design requirements. In this paper, a detailed analysis of the rotor structure is carried out looking at understanding the effects of the geometrical parameters on key performance indexes (e.g. flux density harmonic content, torque capability, torque ripple, etc.). Based on the preliminary analysis, an optimization procedure is implemented for the design of a Nabla-shaped rotor to satisfy the electromechanical performance of a case study traction motor. The results are showing how an optimal machine can be designed with a reduced amount of permanent magnet, by optimizing the rotor structure.

Squirrel-cage solid-rotor core material selection is investigated using a 1 MW 12000 r/min motor as a case study. Different rotor core materials are analysed: S355, X20Cr13, MoCN315M, Imacro M and AISI430. The mechanical strength of the rotor should naturally be strong enough to withstand the high mechanical stresses caused by the high rotational velocity and the rotor should have high saturation flux density for torque production generation. Finite element models are built in Altair Flux 2D environment. A detailed analysis on the influence of material resistivity on torque production and power factor is carried out. Finally, the motor losses are calculated with sinusoidal supply to see the effect of the rotor core material on the motor efficiency.

This paper proposes a new ultra-reliable architecture for fully electric propulsion primarily aimed at the automotive sector. The system considers a direct drive arrangement, minimizing the number of moving components and is based on a network of multi-three-phase machines providing propulsion. The DC-link from each 3-phase star within each machine can be interconnected to form a network, or mesh, which would allow a variety of post-fault mitigation strategies. The system scaling is considered along with the benefits and impact of modularity on device ratings. Finally the simulated performance for one drive is presented demonstrating the core capability in redirecting power flow in case of a fault.

In the framework of the More Electric Aircraft (MEA), weight reduction and energy efficiency constitute the key figures. In addition to these requirements, the safety and the continuity of operation is of critical importance. These sets of desired feature are in disagreement, because the redundancy needed to guarantee the safety of operation implies necessarily in additional weight. Several concepts of the electrical power distribution systems have been proposed, in this manuscript, an approach based on the widespread use of multi-port power converters both for the DC/DC and for the DC/AC stages is proposed. These two technologies allows for a ring distribution of the electrical power whereas the galvanic isolation is still kept. Simulation and experimental results show the feasibility of the concept in common and fault operation conditions.

To reduce the size and weight of aircraft actuators, wide band-gap semiconductor devices (SiC and GaN) are the most promising solution. These devices have switching times well below those of silicon devices. Very short rise times may enhance the electrical stress within the insulation, triggering partial discharges (PDs). The inception of PDs at carrier frequencies of several tens of kHz can lead to the premature failure of the actuator insulation, sometimes in the matter of minutes. In this paper, we show the results of PD measurements at different frequencies and pressures, and discuss the influence of both frequency and pressure on the inception of PDs. Our measurements show a steady decrease of RPDIV with the frequency up to 100 kHz, and a linear dependence of RPDIV on pressure. These findings can be useful to design reliable actuators.

This paper presents the trade-off analysis and design of a high power-density machine for industrial pump applications. The developed permanent magnet synchronous machine drives an electric, oil flooded pump. Different slot/pole combination and winding configuration have been investigated in order to identify the optimal combination that satisfies the electromagnetic and thermal constraint while keeping the losses as small as possible. Several strategies such as the use of the Cobalt iron material for the stator core lamination and the adoption of Halbach array have been investigated in this work to improve the performance capabilities of the designed machine. The electromagnetic performances have been evaluated by using a finite element method. Thermal behaviour has been determined using a lumped parameter network. The outcome of the thermal analysis helped to identify the optimal cooling configurations. The final results are presented highlighting the achieved design targets.

This paper proposes the comparison among different sensorless position estimation strategies suitable for permanent magnet assisted synchronous reluctance machine drives. A machine of such type was designed and optimized aiming at improving its sensorless performance, besides minimizing the torque ripple and maximizing the power factor. Different sensorless solutions for the estimation of the magnetic flux linkage and for tracking the rotor angle are investigated and their performance compared in computer simulations. Experimental results are reported for the PM-assisted synchronous reluctance motor drive example.

This paper presents an extensive study on the electromagnetic and structural influences of the end barrier shape of a Synchronous Reluctance Machine (SynRel). One of the most challenging tasks in designing these machines is to achieve a smooth torque and a mechanically robust structure, especially when high operating speed range is required. Several papers have already addressed the electromagnetic design problem related to the choice of the flux barriers thicknesses and positions. However a comprehensive work on the influence of the end part of the flux barrier on the electromagnetic and structural performance has not been yet presented. In this work two end barrier shapes are considered and optimized using the same methodology. Then the optimized machines have been deeply analyzed in terms of torque, torque ripple and rotor von Mises stress distribution. Furthermore, with the aim to further investigate the influence of such end barrier shape, a detailed sensitivity analysis is presented. In conclusion, general guidelines for the structural and electromagnetic design of such end barrier shape are drawn.

Synchronous reluctance (SynRel) motors with rotor flux barriers are gaining increasing attractiveness in automotive applications thanks to their cheap, rugged and magnet-free rotor construction. When equipped with a split-phase stator winding and supplied from multiple inverters, these machines can exhibit further merits as traction motors in regard to enhanced fault tolerance compared to conventional three-phase solutions. Since SynRel motors are usually designed through iterative optimization techniques, it is highly desirable to have accurate and fast methods to predict their performance without the need for time-consuming finite element analysis (FEA) simulations. An analytical procedure is set forth in this paper to analytically model and simulate a SynRel motor with a split-phase stator winding through a magnetic equivalent circuit (MEC) technique. MEC parameters are computed from analytical formulas describing the air-gap magneto-motive force distribution and the magnetic field inside flux barriers. As an output, the air-gap flux density of the SynRel motor can be computed through the presented technique at any operating point. Results are positively assessed by comparison with FEA simulation on a sample SynRel motor including magnetic saturation effects.