This paper deals with the primary insulation components for the 800 V traction motors used in e-mobility applications. Challenges with the increased voltage level as well as employing SiC converters and oil cooling system are discussed. Focus in this paper is placed on the conductor insulation and slot liners avoiding short-circuit between the conductors, and also between the conductors and lamination, respectively. The study done is based on an extensive laboratory measurement. For each insulation component both voltage endurance and partial discharge inception voltage measurements are carried out, and a comparison between different insulation alternatives is presented and discussed. The measurement results presented in this paper can be well used for proper selection of insulation system depending on the voltage differences between different components and also the expected life-time of the electrical machine.

This paper presents an experimental study on the thermal and efficiency impacts of the hybrid cooling system based on housing water jacket combined with the air- and oil-cooled rotor. The cooling system was designed for an 800 V traction motor used in e-mobility applications. The cooling system configuration and the experimental setup are described. The tests were carried out on a 380 kW prototype motor. The results indicate that the hybrid cooling system reduces both the stator and rotor temperatures compared to standard housing water jacket cooling. Impact of different rotor cooling solutions based on air, oil and a combination of them is studied in detail. In addition, the efficiency and drag losses of the prototype is evaluated under different thermal conditions of the rotor. The losses under different thermal conditions of the rotor are studied and it is shown that the rotor temperature will affect the efficiency on the motor, and different rotor temperatures are beneficial for different operational regions of the motor.

Sustainability aspects of electrical machines are in today’s e-mobility market one of the main requirements together with high efficiency, high power density and low cost. In this paper the environmental impact of the electrical machine is being lowered looking at aluminium hairpin stator winding instead of the conventional copper hairpin winding. Two machines are designed using a multi-objective genetic optimization process with different objectives and compared with a copper hairpin machine design. The increase in resistivity has a non negligible impact on the joule losses, however it tends to mitigate AC effects. Overall, the aluminium hairpin solution is shown to be a sustainable and valid alternative for e-mobility applications.

This paper presents a topology optimization method for reducing specific stator tooth force harmonics which may be considered critical for noise reduction of traction motors designed and developed for e-mobility applications. A design proposal developed for performance and efficiency was analyzed with regards to stator tooth force excitation. The tooth force data was then used to calculate the acoustic power generated by the considered motor. The methodology for the CAE predictions was correlated with measurements. Analyzing the calculated and measured noise radiation from the traction motor, it was found that the overall noise level was dominated by mechanical tooth force order 48 and as a result, focus was put on this harmonic in particular. In order to address the issue, topology optimization was carried out on the rotor barriers of the designed motor with the aim of reducing tooth force order 48, while keeping the other harmonics within the limit. The design output of the topology optimization carried out showed significant reduction in the radiated acoustic noise with minor impact on the motor performance, in the range of 1 percent.

This paper presents a study on different permanent magnet motor topologies that can be used in e-mobility applications. Considering the environmental effects of rare earth elements used in permanent magnet materials, focus in this paper is placed on the solutions with less rare earth element magnets. Additionally, challenges in using non rare earth magnets in the rotor structure of permanent magnet motors are reviewed and discussed. The risk of demagnetization under short-circuit condition is considered as one of the main challenges in using non rare earth magnets that needs attention when designing the electric propulsion system. As shown in this paper, proper rotor design can significantly improve the risk of demagnetization allowing short-circuit in larger operation range. In addition, obtaining an acceptable level of performance and efficiency as using rare earth elements is possible to achieve.

This paper presents a comparative study on traction motors built using random and hairpin winding. Advantages and disadvantages of each winding configuration are reported and challenges of using hairpin winding are detailed. The paper focus is placed on winding copper loss, which is the main root of performance differences in motor equipped by random and hairpin windings. A motor is designed using both winding types. Differences in losses and their effect on motor efficiency is studied. Considering the higher slot fill factor of hairpin winding, DC component of copper losses in hairpin winding has less contribution on the motor efficiency, however, higher AC copper loss is seen in hairpin windings. Thus, motors designed and manufactured using hairpin winding have higher efficiency in comparison to the equivalent random wound motors, especially at high load and low speed.