Typical UAV generator system
Minimising the mass that must be carried by an airframe is central to maximising performance and range. Batteries can constitute a significant part of the overall mass of small to medium-sized UAVs, and so storing the necessary electrical energy in an alternative form is one way of reducing the battery mass.
The gravimetric energy density of liquid hydrocarbon fuels remain more than an order of magnitude better than the best battery technology (12 kWh/kg for aviation fuel versus 0.35 kWh/kg for Li-S). Even allowing for the relatively poor efficiency of internal combustion engines, onboard electric power generation remains a highly effective way of reducing the battery mass.
Existing solutions typically use a brushless DC electric motor configured as a 3-phase alternator as shown on the right. All Millswood Engineering products use this arrangement.
Millswood Engineering makes several UAV generation products:
250W Power Management Unit (PMU). A complete off-the-shelf solution for small to medium-sized UAVs. Includes 3-phase rectification, dual battery chargers, DC-DC conversion to multiple output rails, user-configurable output voltages, CAN and RS232 interfaces, and supports up to 6S battery voltages.
The 250W PMU has been in production since August 2014, and the design has recently had a major revision. It has been installed in many different types of UAV - both fixed and rotary wing - in many different countries. Currawong Engineering have integrated the 250W PMU with several of their engines to provide turnkey EFI powertrain / generator solutions.
900W Power Distribution Unit (PDU). Includes dual battery inputs, DC-DC conversion to multiple output rails, user-configurable output voltages, internal duplication (redundancy) of critical power supplies, CAN and RS232 interfaces, and supports up to 12S battery voltages. Available in IP67 or slimline enclosure.
This is a new product that has been developed in partnership with VISIONAIRtronics of Austria. It has been designed for very high-reliability, with careful use of design compartmentalisation and redundancy. Available second quarter of 2020.
1600W Generator Control Unit (GCU). Companion product to the 900W PDU. When connected together, these 2 products form a complete UAV electrical power generation system. GCU includes 3-phase rectification, dual high-power battery chargers, CAN and RS232 interfaces, engine starter, and supports up to 12S battery voltages. Available in IP67 or slimline enclosure.
This is a new product that is being developed in partnership with VISIONAIRtronics of Austria. Available third quarter of 2020.