Nowadays, one of the challenges in transport electrification is the reduction of the components' size and weight in order to improve the power density. This is often achieved by designing electrical machines with higher rotational speeds and excitation frequencies. In addition, the converter needs to control the machine over a wide speed range given by the mission profile. Therefore, copper losses can significantly increase due to the combination of high frequency excitation and the harmonics introduced by the converter .The winding arrangement design plays a key role in the minimization of the copper losses, thus towards a higher efficiency and/or an improved power density. Different winding topologies can be adopted for high speed electrical machines and amongst them random windings are still one of the most widespread types. This paper presents an in depth study on AC losses in random windings for high frequency motor applications. An analytical method is compared against 2-D Finite Element (FE) simulation results. These are then compared to experimental measurements taken on a custom motorette. Importantly, in order to take into account the random positions of each strand within the machine slots, an Experimental Statistic Method (ESM) is proposed. The ESM allows to define the probability distribution which is useful to evaluate the winding copper losses at the design stage. The contribution of the Pulse Width Modulation (PWM) effect is also considered and experimentally evaluated.

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. The main outcome of this work is the considerable reduction of AC losses by using a segmented hairpin winding.

Nowadays, one of the key challenges in transport electrification is the reduction of components' size and weight. The electrical machine plays a relevant role in this regard. Designing machines with higher rotational speeds and excitation frequencies is one of the most effective solutions to increase power densities, but this comes at the cost of increased losses in cores and windings. This challenge is even more pronounced in preformed windings, such as hairpins, which enable higher slot fill factors and shorten manufacturing cycle times. In this work an improved hairpin winding concept is proposed, aiming to minimize high-frequency losses while maintaining the benefits deriving from the implementation of hairpin windings onto electrical machines. Analytical and finite element models are first used to assess the high-frequency losses in the proposed winding concept, namely the segmented hairpin, proving the benefits compared to conventional layouts. Experimental tests are also performed on a number of motorettes comprising both conventional and proposed segmented hairpin configurations. Finally, these experimental results are compared against those collected from motorettes equipped with random windings, demonstrating the competitiveness of the segmented hairpin layout even at high-frequency operations.

Nowadays, electrification in the transportation sector is one of the most viable solutions to reduce CO2 emissions and meet fuel economy requirements. Being the electrical machine one of the most important players in this electrification trend, extensive research is currently being dedicated to the improvement of their efficiency and power density. In automotive applications, hairpin technologies are widely spreading due to their potential in reducing costs and life cycles in a mass production perspective, as well as in increasing the torque capabilities of machines. However, several challenges need to be addressed before the complete replacement of random windings with hairpins can take place. Of these challenges, the loss produced during high frequency operations is one of the most limiting. This paper aims at studying and investigating high frequency (AC) losses for different slot geometries and conductor cross sections, which in turn involve the analysis of different slots-per-pole-per-phase / layers-perslot combinations. In addition, the effects on the AC losses of reducing the slot fill factor are studied, either by removing the closest conductors to the slot opening or by reducing the hairpin legs' height. Analytical and numerical models are employed to investigate these concepts.

Nowadays, Interior Permanent Magnet Synchronous Machines (IPMSM) are widely adopted in various sectors such as automotive, railway or public transportation (ebuses, 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.

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