January/February 2024 | E-Mobility Engineering 30 intentional in our inverter, as is our PCB layout, which is designed in-house, including our own gate-driver circuitry,” says Sylvestre. “A lot goes into our gate-driver design to minimise inductance and interference between circuits, and to define return paths. EMI issues in a circuit often stem from poor return-path routing. We’ve also got galvanic isolation between the LV controller and the higher-voltage gate drivers and other HV parts, and so a lot goes into ensuring proper clearances, creepage distances and HV insulation, including minimising stray capacitance at the interfaces between the HV and control circuitry. “Of course, developing a secure supply chain is critical for developing SiC inverters. We’ve got an excellent working partnership with Wolfspeed, which is one of our SiC suppliers and probably one of the biggest out there, and we work very closely with them on product development, production planning and road-mapping future core-technology improvements. Lead times for SiC are still long, and there are constant highvolume orders for Wolfspeed’s product, so we work closely with them to ensure we have the inventory we need when we need it,” Sylvestre adds. Configuring the gearbox The gearbox is a single-stage, singlespeed device, and this mechanical simplicity is ideal for aerospace as it minimises maintenance. It is an epicyclic gear system (arguably better known as a planetary gearset), which H3X has designed in-house to optimise its power and torque densities. “It’s set to come in two standard configurations: one we’ve already alluded to, and that has a trapped volume of oil in it, which gets churned and splashed by the planetary gears in order to lubricate everything and cool the gearbox components,” Liben says. The other option that H3X is developing consists of a gearbox configuration designed to function with an external oil pump and filter. While this will make for a more complex and heavy arrangement, the company anticipates it may make maintenance easier; for instance, by enabling longer intervals between oil changes. “While our lower-power products require this gearing in many applications, we anticipate that the majority of applications for our future products above 320 kW will be capable of directly driving the load, with all the benefits of reduced maintenance that follow from that,” Liben adds. Motor control In the HPDM-30 and -250, a dual-core microcontroller unit (MCU), optimised for motor-control applications, is built into the inverter, and multiple such controllers can be run simultaneously on a common bus. The integrated motor drive requires a command setpoint to be sent to the unit, and the user can request torques, speeds or bus voltages, depending on which of the three corresponding modes is set to ‘active’ (the former two request modes apply best to propulsion configurations, while the third is meant for powergeneration applications). Considerable internal information on the powertrain is tracked via sensors, which can be provided to the vehicle’s comms bus, and hence to the operator or technicians. These include heat measurements at every crucial location where hotspots can form (such as the motor windings, SiC power modules and bearings), including a non-contact, infraredbased sensor for gauging the rotor shaft’s temperature in the HPDM-250. In future, H3X plans to implement more data-focused features, such as accelerometers to estimate the remaining lifespan of bearings based on acceleration and vibration profiles, and a means of detecting noncatastrophic winding faults via current measurements. While temperature measurements can pick up both things indirectly, H3X feels it prudent to develop additional approaches to maximise robustness via diverse sensing methods, and to one day enable more powerful predictive maintenance indicators. The torque request mode is the most straightforward: the inverter regulates the phase current supplied to the motor to achieve the user’s desired torque output. Speed control is implemented via an outer control-loop around the torque-control subroutine. Upon receipt of a speed request while the user has set the powertrain to speed-control mode, the outer loop regulates and changes the torque request to maintain the corresponding rpm speed. In the power-generation mode for hybridised powertrains, the controller can regulate the inverter’s HV DC bus to maintain a setpoint voltage by regulating Dossier | H3X H3X plans to expand production of the HPDM-30 and -250, and have test versions of the -1500 ready to ship to customers by the end of 2024
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