The modeling of a PEM fuel cell — Supercapacitor — Battery system in dynamic conditions

Today the application of PEM (polymer electrolyte membrane) fuel cell stack in the automotive field is a topic on central interest. Unfortunately, a PEM fuel cell stacks cannot directly supply variable speed drives because of their non-linear behaviour in dynamic conditions. This paper is mostly concerned with the performance evaluation of the PEM fuel cell-supercapacitor system during repetitions of current step variations; in those cases, the supercapacitors cannot be completely recharged before supplying the load in the next dynamic, and the fuel cell stack can be overloaded. We propose the introduction of lithium battery packs and of a DC/DC converter. The obtained results shows that with the proposed configuration, the size of supercapacitors can be significantly reduced, reducing the stress on the battery pack without losses of performance. That will be useful in the design of the control strategy of variable speed drives supplied by the proposed system.