Unmanned Systems Technology 022 | XOcean XO-450 l Radar systems l Space vehicles insight l Small Robot l BMPower FCPS l Prismatic HALE UAV l InterDrone 2018 show report l UpVision l Navigation systems

58 Dossier | BMPower fuel cell power system use liquid cooling and for our FCPS you don’t need to ‘prepare’ the hydrogen [to humidify it, for example]. Our strategy is to create a simple system to ensure minimum weight and to maximise the simplicity of operation.” Overview In simple terms, any fuel cell converts the chemical energy of hydrogen into electricity using an electrochemical process. Hydrogen offers a high energy intensity (its figure of 140 MJ/kg is three times that of gasoline) and it should be noted that the conversion is achieved without the use of a combustion process and without the need to transform thermal energy into mechanical energy. BMPower exploits a hydrogen-air fuel cell with a proton-exchange membrane (PEM). The membrane creates electricity through a chemical reaction between positively charged hydrogen ions (protons) and oxygen. Unlike a battery, it needs a continuous source of hydrogen and oxygen to sustain the chemical reaction, but so long as those inputs are supplied it will generate electricity. A PEM-type cell is the most mature technology with the highest power density. In this type of cell, a proton- conducting polymer membrane separates two electrodes, an anode and a cathode, each with a catalyst applied to it. Hydrogen disassociates on the anode, yielding protons and electrons. Unlike the protons, the electrons are unable to pass through the membrane, and instead travel to the cathode through an external circuit; thus is the electrical output generated. At the cathode, the electrons associate with the protons and oxygen to form water, which is the only product of the reaction (in the form of steam and/or liquid). A fuel cell module includes a number of cells connected in series to provide a useable working voltage (much like a battery). The only inputs to the module are oxygen from the atmosphere and hydrogen gas; its outputs are electricity, water vapour and heat. The electrical output of the BMPower FCPS is regulated by its electronic control system to be anything from 10 to 100 V. Ivanenko notes that it can be held at a given voltage ±1 V on a sustained basis, and if necessary the control system can replicate the behaviour of a lithium battery, such as a given craft would have been designed to use. The basic BMPower FCPS is the 1000 (nominal 1000 W output) but also available is the 500 ‘half-unit system’ plus the 2000 and 3000 double- and triple-unit systems. As of September 2018 a small 150 (nominal 150 W) system has been added to the range. Hereafter we describe the basic, single full-unit 1000 system. The BMPower 1000 FCPS consists of four elements. Aside from the fuel cell module itself, there is the fuel processing system that incorporates a hydrogen cylinder, a pressure regulator, a gas connector and the necessary plumbing and wiring between those items, and the third major element, which is the control module. The fourth element is a buffer battery. The BMPower fuel cell module has its main metal structure containing the cells on top with four plastic fans and ducting at its base, those sandwiching a carbon composite section. It has been designed to be very rugged, notes Ivanenko. The FCPS uses a PEM fuel cell with an open cathode. That means the cooling air supplied by the four fans at the base of the module provides the oxygen the cells require. A ‘closed cathode’ tends to last longer, Ivanenko acknowledges, The BMPower 1000 W fuel cell module seen from the bottom showing the four fans A hydrogen cylinder as supplied by Linde Gas October/November 2018 | Unmanned Systems Technology