22 January/February 2024 | E-Mobility Engineering in-house manufacturing. Being highly vertically integrated has enabled a process of rapid development. Liben estimates that since December 2021, H3X has produced an average of one new prototype per month (26 to date) to test and validate new improvements for airworthiness and specific power. System concept and architecture All of H3X’s products are integrated motor drives, containing a permanent magnet synchronous electric motor, a SiC inverter and, in some cases, a planetary gearbox. These co-optimised systems are packaged together, sharing an additively manufactured structural housing with what H3X calls ‘synergistic cooling’. “They are actively liquid-cooled, with the coolant channels formed inside the walls of the housing as it is printed. Having common mounting points and cooling channels for our motor and inverter saves a lot of complexity and mass in our design, compared with using COTS cooling plates,” Liben says. Notably, the HPDM-30’s electromagnetic cross-section is identical in design to that of the HPDM250 except for a shorter stack length, so their diameter is the same inside their housings. With their housings, they are 130 mm and 225 mm wide, respectively. The HPDM-250 is also wider due to its inverter being constructed radially around the motor (the HPDM-30 inverter is packaged axially behind the motor). Both motors are designed with 12 slots for the stator winding and 10 magnet poles in their rotors (12s10p). Vital benefits of 12s10p “A crucial benefit of the 12s10p approach is that the three phases of the stator are magnetically decoupled from each other. That gives us very sinusoidal line voltages and currents, and hence very fine motor control and low torque ripple, even under extremely high magnetic saturation,” Liben says. “We also use a concentrated winding with very short end-turns – much shorter than the typical full-pitch winding. Combined with 12s10p, we get a winding factor [a measure of stator design effectiveness and an indicator of torque density, calculated as a function of the windings’ distribution factor, pole factor and skew factor] of over 93% with very low end-winding losses.” The larger HPDM-1500 is a multisector machine with eight drive sectors, each equivalent in essence to one HPDM-250. To explain how the scaling works, H3X recommends first imagining the HPDM250’s circular 2D cross-section and unrolling it into a line, creating a linear motor. If that line is copied and pasted eight times, a linear motor is created that is 8x longer. Finally, if one takes that line and rolls it back up into a much larger circle, the per-sector geometry remains approximately constant, so H3X can use the HPDM-250’s inverter and electromagnetic design for each drive sector in the HPDM-1500. “Our winding method could also be used to make a more common 12s8p e-machine, but that would have performed weaker in every respect except vibration and acoustic noise,” Liben says. “We’ve engineered our motor housings to suppress noise as far as we can. To a certain extent, a 12s10p e-motor will always be noisier than a 12s8p one, but when you’re driving a propeller or generating power from an engine, you typically can’t actually hear the e-motor over the prop or engine. We’ve observed that multiple times during our iron bird and integrated vehicle testing, and there will generally be noise isolators on the vehicle side to further keep conducted acoustic noise from propagating to passengers,” he notes. In the HPDM-1500, each of the eight drive sectors is isolated thermally, mechanically, electrically and magnetically from the others, meaning any faults will rarely propagate between them, and a faulty section can be shut down without significantly affecting operations. Such failover mitigation would not be possible with a 12s8p baseline motor winding (or with any traditional distributed or fullpitch winding) due to the presence of magnetic coupling between phases. Building bigger “The 1.5 MW HPDM-1500 serves as a building block for future 3 MW to 9 MW powertrains by stacking multiple -1500s along a common rotor shaft,” Sylvestre says. “The impact we can have from a decarbonisation perspective is directly linked to how much power we can install per application, so we very much want to develop larger and Dossier | H3X The HPDM-250 produces up to 200 kW of continuous power, and currently weighs 18.7 kg, though H3X has a development roadmap to bring this down to 16.6 kg
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