The ET-6 high density electric propulsion motor developed by PMC duplicates the power output characteristics of a PT6 turboshaft, including the same propeller interface, with just 115 kg mass.
Propeller speed is up to 2200 rpm and peak power exceeds 750 kW. ET-6 connects directly to the propeller and therefore does not require a gearbox; it has extremely simple mechanics and virtually no wear parts except grease lubricated hybrid bearings with inspection intervals greater than 5000 hr.
Rotor is permanent rare-earth surface magnets type, with magnets secured by a carbon fibre ring, preloaded to ensure a compression load even in overspeed conditions.
The shaft is made of titanium alloy for lightness. The propeller axis is hollow to house the governor mechanism. The angular contact, preloaded ball bearings are of the hybrid type to minimize lubrication requirements.
High efficiency liquid cooling circuit surrounds the stator while the rotor does not need cooling. All the structural parts of the motor are made of high strength light alloy, machined from solid with no welds or castings.
From an electrical system point of view, civil aviation currently uses the automotive standards that provide for a battery voltage range 850 to 650 Vdc, to take advantage of the wide availability of semiconductors optimized for these voltages.
A 2000 Vdc standard for large aircrafts might be possible in future.
To optimize availability and safety, as well as to allow the use of modular and high frequency drives, the motor winding is divided into 4 autonomous and independent sections, operating as separate motors. This limits the current per section to about 400 A, with advantage in redundancy and drive size optimization.
Frameless hybrid permanent magnet motors, developed to be positioned directly on the propeller axis which in turn is the output of an IC or turboshaft engine.
The starting power required for take-off is provided by the sum of the power of the IC motor and the electric one, powered by a small battery.
This motor has a thin ring configuration, without bearings, cooled on the outside, with permanent FeNdB magnets positioned on the surface of the rotor and secured to the rotor by a preloaded carbon fibre ring, while the stator is divided into two independent windings that allow the use of two drives.
EXPERIMENTAL HIGH DENSITY DRIVES
• Inverter capable of 400 A three-phase, continuous, with DC bus 850 Vdc.
• Water/glycol cooling
• SiC devices sintered directly on the silver heatsink.
• Current sensors integrated on the output busbars.
• Modular and synchronized drives for each winding, to drive high power units
• Weight 2.9 kg – Volume 3.75 dm3
• Power managed with 800 Vdc bus is 370 kVA (typically 340 kW if the cos-fi of the motor >=0.9) 117 kW/kg and 90 kW/dm3
