76 so highly optimised code and using a costly but quality DSP was critical for making sure each system synergistically worked together,” Ricci notes. Self-cooling While different liquid-cooled versions of the DHA120 are available, particularly for high-altitude UAVs flying above 40,000 ft, where insufficient air for cooling is available, all run significantly heavier than the standard, air-cooled version. Regarding how the 4.5 kg, 40 kW generator is self-cooled via air, Ricci explains: “The flat, spinning surfaces in the air gap function as an impeller via surface friction. If you look into ‘tesla turbines’, those are flat, bladeless discs that spin relative to each other and actually pump water, without needing vanes.” Historically, metallurgy was not advanced enough in Tesla’s time to engineer tesla turbines effectively, but today’s research is yielding promising results for their use in industrial and medical applications. In LaunchPoint’s application, the highspeed spinning of the rotor drags air into the rotor-stator gaps by way of surface friction, entering through the gaps in the rotor plate and running in a circular pattern, with centripedal force then driving the air out of the gaps. “The high speed of the air creates a lot of turbulence, which is perfect for good convection. We get almost liquid-cooling levels of convection inside the air gap,” Ricci says. “And it’s a very small, thin, turbulent boundary layer, so the turbulence doesn’t exert enough force to cause any damage or drag inside the motor.” The HPS400’s other components, such as the PMU and BMS, do not use any of the motor-generator’s airstream as this would require mounting them on or close to the engine, where huge vibratory or heat hazards would be presented. Instead, their enclosures are designed with heat sinks, and fans where necessary, their placement and mounting throughout the UAV to be optimised between LaunchPoint and each specific customer. Control systems The PMU’s DSP covers all motor and engine control functions, plus monitoring and communication with the LaunchPoint BMS. The PMU also contains the engine’s ignition control module, and the company’s CAN bus (based on an earlier protocol used by NASA, since expanded for the integrity and prioritisation requirements of LaunchPoint’s powertrains). “The CAN protocol is simple, but can have up to 64 of our devices on the same bus, so UAVs needing two generators, two BMS, multiple PMUs working as motor controllers across an airframe, can all share a common bus and work together by monitoring each other’s realtime data,” Ricci says. Both the passive and active configurations of the HPS400 use similar control algorithms, although the latter naturally has more functions, and more operational and control degrees of freedom. Across both, the PMU essentially runs a power control algorithm, with sensors connected across both PMU and BMS first taking load measurements from the UAV to determine how much power must be supplied (with the battery and powertrain treated by the software as a single, unified power source to the DC bus). “The PMU then determines how the engine needs to run to generate power per load, with a feedforward algorithm June/July 2024 | Uncrewed Systems Technology HPS400 Hybrid-electric Complete system weight: 69 kg active configuration, 64 kg passive configuration Bus voltage: 420 V DC or 210 V DC active configuration; 210 V DC or 104 V DC passive configuration Maximum power: 40 kW Maximum continuous power: 35 kW at 6500 rpm Specific fuel consumption: 566 g/kWh at 35 kW Rotax 582 engine Two-stroke Inline two-cylinder Spark-ignited Liquid-cooled Oil-injected Dry weight: 41.4 kg Displacement: 580.7 cc Maximum power: 48 kW (64.4 hp) at 6500 rpm DHA120 Permanent magnet synchronous motor-generator Axial-flux Dual Halbach array rotors Ironless stator Neodymium iron boron permanent magnets Litz wire windings Passively air-cooled Weight: 4.5 kg Diameter: 317.5 mm Length: 45 mm Key suppliers Bearings: SKF Digital signal processors: Texas Instruments Litz wire: New England Wire Technologies Radiators: Rotax Servos: Futaba SiC transistors: Wolfspeed Current sensors: LEM Heat sinks: Cool Innovations Connectors: Amphenol Key specifications
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