Dynamic behavior and transient analysis are one of the most critical issues for high performance polymeric electrolyte membrane fuel cells. An improvement of performance can be achieved both with hardware modifications and with more sophisticated control strategies. To this regard, the availability of a reliable dynamic fuel cell model plays an important role in the design of fuel cell control and diagnostic system. This paper presents a non-linear, iso-thermal, zero-dimensional model of a pressurized PEM fuel cell system used for automotive applications. The model was derived from a detailed, iso-thermal, steady-state, dimensional model which explicitly calculated (and subsequently captured as a multi-D look-up table) the relationship between cathode and anode pressures and humidity and stack average current. Since in the electrochemical model the single cell performance depends on the membrane ionic resistance, which is strictly related to the membrane water content, a dynamic estimation of the membrane water diffusion has been considered. This takes into account the dependence of the cell voltage on the unsteady membrane water concentration. A similar approach still allows the development of a simple zero-dimensional dynamic model suitable for control system development and amenable to control-oriented humidity modelling.

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