30 While the topology requires some elaborate models and algorithms for PWM control to ensure optimal performance, limiting the choices of COTS inverters that can work, the H2D2 project was fortunate enough to still find a suitable inverter. The resulting rotor design uses seven small magnets per pole, each magnet being identical to optimise and simplify both the assembly process and supply orders. The project partners note that only three part references (the magnet, lamination and shaft) need to be accounted for in the rotor. Overall, the rotor features four pole pairs, while the stator is designed with 48 slots, as well as a distributed, three-phase winding, chosen to reduce the losses in the rotor. These active parts of the electric motor were developed via an algorithmic optimisation process, designed and honed by IFPEN. In this approach, the company’s proprietary algorithms first use input variables to generate response surfaces, and then the stator and rotor geometries are optimised using the response surfaces to identify the overall optimum motor design. “This methodology minimises the computation time needed for realising the optimisation, and the exploration and optimisation tool at the heart of our approach integrates its own automatic rotor, stator and magnet geometry generator, which is managed by the mathematical layer,” Milosavljevic explains. “This tool has proven very handy for exploring the best geometries for a given set of specifications and constraints, as well as for finely optimising the complete geometry of any active motor part under particular mechanical, thermal, industrial and system constraints – including those imposed from the vehicle, the inverter, the battery, the fuel cell, and so on.” Motor cooling Additionally, the motor uses a cooling system jointly-patented in 2020 by EREM and IFPEN from a previous joint project, having been successfully adapted to the H2D2 powertrain. The thermal management approach is optimised around a simple, waterglycol cooling circuit with a costefficient potting of the stator coil to enable consistent high performance (particularly consistent torque) with reduced heat loss. As described in the patent, the stator cooling circuit consists of tubes that pass longitudinally through the stator body, and through the potting material about the coil heads. Those tubes are typically connected by channels located in the motor flanges, resulting in a serpentine form for the cooling circuit around the stator and coil heads. “We also chose materials for the mechanical parts that would maximise thermal conductivity, to extract heat from the rotor and stator as fast as possible. Having the coolant in close contact with that material is really important,” Maier says. EREM developed a unique method for stacking the rotor laminations and inserting the magnets, which was validated for the first time on this motor. Maier says optimising the methods and tooling for rotor construction has been one of the biggest challenges to solve in the project. “We stack the laminations one by one, and then we compress them, install the permanent magnets, and lastly add the thermal potting resins. The stator construction is analogous, starting with stacking and then compressing the steel laminations before inserting Dossier | H2D2 snow groomer Extensive testing of the snow groomer in real-world ski-slope conditions will continue this year, with final modifications and adjustments by Q1 2025 (Image courtesy of PistenBully) May/June 2024 | E-Mobility Engineering
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