29 H2D2 snow groomer | Dossier high-power motors at the scientific level today, and required a big effort in the design phase from EREM,” Milosavljevic says. EREM went on to develop the required tooling and produce the complete set of parts before assembling two initial motor prototypes, which were delivered in November 2022 for testing and vehicle integration. In parallel, EREM purchased the aforementioned inverters and received them in July 2022. The prototyped powertrain was validated at IFPEN, with some help from the inverter supplier (particularly in adapting the inverter software to the motor). Validation was executed in multiple phases by order of priority. The first release of the powertrain in February 2023 brought the opportunity to use it in the slow groomer for the first time, with the final release following in October 2023. The powertrain is now operational in the snow groomer prototype, and it has also been integrated into another vehicle for testing and validation in harsh environments (with particular attention being paid to its vibration and very high temperature performances). Permanent magnet- assisted synchronous reluctance motor In addition to fulfilling the peak power, speed and torque targets discussed above, the snow groomer’s motor is a radial-flux machine, measuring 360 x 390 mm and weighing 170 kg. Such are its design and optimisation that it produces about 760 Nm of continuous torque from 415 ARMS (while running under test conditions consisting of a 700 V supply, a 500 rpm shaft speed and a 25 C ambient environment). The system’s peak torque output is 870 Nm, and through testing, the company found that so long as the liquid-coolant circuit functions well in cooling the stator, the motor can be run at low shaft speeds to continuously maintain 77% (675 Nm) to 86% (750 Nm) of the peak torque value. “Our test results show a significant difference from existing solutions on the market, which typically present continuous torque at 50% or 60% of the max torque value, while our solution keeps a competitive level of compactness in its physical dimensions and simplicity in its cooling design, but also achieves continuous torque of around 80% of our maximum torque capability,” Milosavljevic adds. Through their joint research, the project partners eventually deemed the permanent magnet assisted synchronous reluctance (PMSR) topology as the best option for designing a motor capable of reaching high performance levels with the minimum of environmental impacts, costs and supply risks in its manufacturing. The rotor was designed and optimised by IFPEN through a multi-physics, multi-criteria workflow (covering motor geometry, electromagnetics, mechanical design and thermal performance), resulting in a patented design for the rotor laminations. A key benefit of the PMSR topology (and a key point of focus with respect to the rotor) was that its rotor uses electrical steel to produce over 60% of its torque, with the permanent magnets only assisting in the remaining 40%; that reduces the size of the inverter needed, the quantity of magnets needed per unit, and enables constant power performance up to high speeds. A 15 kg off-the-shelf inverter was found as a match for the motor. Measuring 328 x 298 x 134 mm, it runs on silicon-carbide transistors (Image courtesy of IFPEN) E-Mobility Engineering | May/June 2024
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