State estimation with time delay and state feedback control of cathode exhaust gas mass flow for PEM fuel cell systems

Polymer electrolyte membrane (PEM) fuel cells are highly efficient energy converters and provide electrical energy, cathode exhaust gas with low oxygen content and water. On aircraft fuel cells have the potential of replacing the auxiliary power unit (APU) that is currently used for electrical power generation during ground operations. An APU is a significant source of noise and greenhouse gases. PEM fuel cells, however, can significantly reduce these pollutants. In this study a PEM fuel cell system is investigated for generation of oxygen depleted cathode exhaust air (ODA). This gas is intended for inerting on aircraft and must have a low oxygen concentration. A nonlinear simulation model comprising the fuel cell stack, stack cooling system and cathode exhaust gas dehumidifying system has been developed and a reduced order model for controlling ODA-gas mass flow was derived. An observer for state estimation combined with a predictor to compensate for the large time delay occurring has been designed. ODA mass flow is controlled for by a linear state feedback controller. Simulation results performed at the nonlinear simulation model in Matlab/Simulink® and experimental results are shown.