To enhance the fault tolerance of modular multi-unit three-phase PMSMs, this paper investigates the influence of pole-slot combinations and stator slot geometries on inter-phase magnetic coupling. A novel open-slot structure with fault-tolerant teeth (FTT) is proposed to improve magnetic decoupling and unit-level independence.Two configurations— 40p48s and 40p36s—combined with three slot types are analyzed via finite element simulation. Flux distribution and inductance matrices are obtained to quantify magnetic coupling, and a coupling coefficient is defined for comparison.To evaluate short-circuit performance, turn-to-turn faults of varying severity are introduced via an external circuit model. Results show that the 40p36s structure with FTT provides superior decoupling and fault containment, enabling continued operation of healthy units without control intervention.

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.

This paper describes the conjugate thermal analysis performed on an traction electric motor for electric vehicle (EV). The machine considered adopts hairpin windings and the cooling is achieved by combining an external water jacket and internal oil spray on the end-windings which is delivered by high pressure nozzles. The thermal characterization was performed in two stages; in the first stage the thermal performance of the original design was investigated whilst in the second stage some solutions were proposed to enhance the cooling effectiveness. Due to the heavy computational cost of the analyses, performed by the means of Computational Fluid Dynamics (CFD), fluid flow and conduction heat transfer were investigated separately. The results produced have shown that despite the good overall cooling capabilities of the spray, some issues may arise when the motor operates at low speed-high torque condition as the number pin layers increases. In this scenario droplets might struggle to penetrate through the conductors, leading to localized hotspots. It is also found that minor adjustments of the position of the nozzles may considerably improve the heat transfer rate. The realistic 3D representation of the conductors has allowed to further improve the accuracy of the analyses carried out.

The initial position estimation is an important issue in position sensorless control, which is also applied to Triple Three-Phase Surface-mounted Permanent Magnet Synchronous Motor (TTP-SPMSM). It is thought to be difficult to estimate SPMSM's initial position because of the lack of saliency. This paper proposes an initial position estimation method for TTP-SPMSM based on high-frequency voltage injection. The inductance spatial harmonics in the considered TTP-SPMSM enables estimation of the initial position. This paper presents the principle and verification in the simulation of the proposed method.

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.

Recently, the synchronous reluctance machine limits have been pushed toward meeting the requirements of traction applications. A skilled electromagnetic architecture of a synchronous reluctance machine with the help of permanent magnets can push the limits of power density and speed range to that of traction applications, however, the mechanical integrity of the rotor can still be in question. A traction application means large rotor diameter and high rotational speed, two criteria that makes a challenging design, in particular, mechanically. In this paper, the multi-physics design steps of a permanent magnets assisted synchronous reluctance motor for automotive application, have been presented. Firstly, the electromagnetic design following the size and thermal aspects and constrains has been conducted. Secondly, methods to reduce the mechanical stress has been explored and a bridged mechanical design has been adapted. Finally, thermal analysis of the machine has been conducted to ensure the thermal limits have been satisfied.

Electrical machines with high torque density are required for traction application. Availability of bonded magnets with complex shapes and magnetization pattern can significantly extend the design space of electrical machines. This paper introduces a hybrid flux barriers design to improve the torque density of permanent magnet assisted synchronous reluctance (PM -SynRel) machine using ferrite magnets. The torque density with hybrid flux barriers is found to improve along the entire range of speed compared to the conventional flux barriers. The hybrid barrier design achieves similar performance to that of curved barrier with relatively flat shaped magnets in the last flux barrier. Thus, the hybrid barrier is able to enhance the torque density at a potentially reduced cost of manufacturing. The hybrid flux barrier design is validated for both electromagnetic and mechanical performance using commercial finite element analysis (FEA) packages.

High power density and high torque density are the fundamental requirements for electric machines used in traction application. The former is obtained by potentially increasing the speed of the machine while the latter by using high energy density rare earth magnets. Ferrite magnets are explored as a viable alternative to rare earth magnets which are relatively expensive and geographically concentrated. The paper is intended to bring out the current trend of electric machines used in electric vehicles (EVs) with due focus on permanent magnet assisted synchronous reluctance (PM-SynRel) machine. High power and high speed PM-SynRel machine with rare earth and ferrite magnets are designed and compared based on the requirements for a future electric commercial vehicles. The ratio of stack length, mass of magnet, total mass and inertia of rare earth machine in comparison to ferrite PM-SynRel is found to be 0.72, 0.42, 0.72 and 0.32, respectively. Based on these, the rare earth based machine is found to have high power density, torque density and also utilizes lesser volume of magnets but PM-SynRel with ferrite is getting closer.

This paper proposes a semi-flooded cooling concept for a high speed machine design. The electrical machine considered is for an aircraft starter-generator system where power density and efficiency are crucial. In order to achieve the high power density permanent magnet machine, a direct oil cooling strategy for the machine stator is adopted. A stator oil sleeve is designed to separate the machine into an oil-flooded stator chamber and an oil-free rotor chamber to avoid windage loss due to the high rotor speed. Different materials, Carbon Fiber (CF) and E-glass fiber (GF) are considered for the oil-sleeve design. Implications of the aforementioned materials on the structural design are investigated and optimized accordingly using finite element methods. It is shown that the oil sleeve made of CF provides structural capability with a minimum sleeve thickness. However the sleeve made from GF has the benefit of having no electrical conductivity. Both oil sleeves are made and the GF sleeve is successfully applied to the machine and tested.

The development of new power electronic device and high performance magnetic materials are the main technological factors that have led both industries and research community to focus their attention on high speed electrical drives. Several papers have already outlined the electrical machine and/or converter topology choice for certain high speed application. This choice obviously depends on the applications under study. This paper aims to identify the most important high speed applications. For each of them, the main design challenges are highlighted and an overview of the already available product on the market is presented.

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.