Article published Fuel cell
Health report instantaneous and in-situ
LIST has developed a controller which measures the state of the voltage of each individual cell of a fuel cell. This is a key point for evaluating its state of health. This system is suitable for any type of electrical power supply made up of individual cells.
Controlling the electrical functions of a hydrogen vehicle assumes an accurate knowledge of the state of health of the generator, made up of around a hundred adjoining individual cells in which chemical reactions are taking place, which convert hydrogen and oxygen into electricity, heat and water. Each individual cell only delivers a voltage of between 0.3 V and 1.3 V. If some of these cells are defective, or in an unstable regime, as can be the case during commissioning of the fuel cell, then performance of the entire fuel cell may be degraded. “Hence the importance of accurately knowing the state of the voltage for each cell”, indicates Fabrice Auzanneau, team leader for Reliability of embedded systems at CEA LIST. This was the objective assigned to his team in the FISYPAC research project, led by PSA Peugeot Citroën and financed by the French National Research Agency (ANR). The objective was achieved after several months.
A highly innovative electronic device, designed and produced by CEA LITEN, which connects to a fuel cell and enables the cells state of health to be checked while it is in operation, by measuring the voltage across each of the component cells. The device reports to the vehicle's central computer using the vehicles own communication protocols. “The circuit boards are fixed directly onto the armature of the fuel cell and are tested and checked in the vehicle under normal conditions of use, by measuring the voltage of 240 cells over several hundred milliseconds”, explains the researcher. One of the important constraints to observe for such equipment concerns electrical insulation. The instrumentation developed must be able to support a transient voltage of 1 ,500 V in comparison the vehicle reference, whereas the normal operating voltage of fuel cells is 300 V and its current 200 amperes. Insulation of the circuit board is provided by optoelectronic components. Three patents have been filed in relation to this device and a fourth has been filed for a second device based on sensors using GMR technology(giant magneto resistance). Developed by the IRAMIS*, these sensors have the advantage of being intrinsically insulated (the current of each cell is directly transformed into a magnetic field which is detected by a GMR sensor). This gives a more integrated solution: an array, 3 mm by 1.5 cm, making it possible to acquire signals from 8 cells. “These generic developments can be applied to any power supply, whether vehicle electrical batteries, hybrids or even fuel cells for other non-automobile applications, in the home for example”, adds Fabrice Auzanneau. In fact, even if the electricity management system differs, a battery is an arrangement of elementary cells which produces electricity. Numerous industrial and research partners are envisaged.
*Institut Rayonnement Matière - Institute for the Irradiation of Matter - at Saclay
