Unmanned Systems Technology Dec/Jan 2020 | Phoenix UAS | Sonar focus | Construction insight | InterGeo 2019 | Supacat ATMP | Adelan fuel cell | Oregon tour | DSEI 2019 | Copperstone Helix | Power management focus

28 December/January 2020 | Unmanned Systems Technology sufficiency in energy – thus relied on being able to create an onboard power generation, storage and distribution system that could supply the pumps and valve that open the airway to the internal bladder. In addition, it had to compress the air and vent it back to the atmosphere, and supply the actuators for the aerodynamic flight controls and the onboard autonomous flight control system. The pumps and valve were developed by TCS Micropumps, while the actuators were specified by the UHI and sourced by TCS. The electrical system was designed and managed by the University of Southampton (working with IQE, TCS Micropumps, CPI and MTC) and is shown in Fig. 5, where the battery system directly supplied the main DC power link, received power input from the photovoltaic (PV) system via a Maximum Power Point Tracker (MPPT) unit and would have delivered or received power to/from the reversible hydrogen fuel cell (HFC) unit (had it been included) via a bespoke DC-DC converter. This converter is required as the fuel cell operates with a voltage level typically between 9 V DC at no load (0 A), to 6 V at 30 A (nominal 250 W rated, including losses), and has to interface to the battery with a nominal voltage of 48 V DC. The battery consists of COTS lithium-ion cells (chosen for their high energy density, safety features and relative cost) arranged in 13 parallel strings each of 13 cells in series, giving 169 cells overall. This arrangement provided a degree of redundancy, so that the failure of a cell would affect a single string, not the entire battery. Each cell has a nominal voltage of 3.7 V, with a realistic charge storage capacity of 3-3.2 Ah per cell (less than the manufacturer’s rated 3.5 Ah). This resulted in 48.1 V per string and, with 13 strings in parallel (3.2 Ah x 13 x 48.1 V), Fig. 5 – Block diagram of the Phoenix’s electrical system Fig. 4 – The tail components are held together on a tail-box frame that fits over the cone-shaped rear end of the fuselage Fig. 6 – Diagram of the Phoenix’s battery system