Response of a hybrid supercapacitor - PEM fuel cell system to fast fuel cell energy dips

PEM fuel cell (FC) operation is likely to be characterized by voltage dips on time scales shorter than 1 s, arising from temporary flooding of gas channels or porous layers, particularly when the FC is operated at high humidity levels. If supercapacitors are employed together with the FC as energy storage systems, they can make up for the temporary lack of energy produced by the FC. However, the steep slopes of the voltage dips affect the energy that can be actually delivered by the supercapacitor because of the frequency dependence of its capacitance, and this should be taken into account in sizing the supercapacitor. In this paper, the supercapacitor response to a FC voltage dip is simulated and discussed, based on an experimentally identified supercapacitor model and a typical voltage dip measured on a single PEM FC.