Modeling and analysis of thermal-management impacts on transient performances of PEM fuel cells

The characterization of transient performance is necessary in the design, control and diagnosis of PEM (proton-exchange membrane) fuel cells. The operating temperature of the fuel cell plays a very important role in the middle-and long-term cell dynamics, and the impacts of a thermal management system must be considered. This study focused on the modeling and analysis of the system-level cell dynamics, which have a close relationship with the operating temperature and the cooling conditions of fuel-cell modules. Mathematical models were established by modeling the energy-conversion phenomena inside the fuel-cell stack and the heat-dissipation process by the thermal-management system. The output equations for the calculation of the electrical power and voltage were additionally deduced from electrochemical theory. Four typical disturbances, including step changes in electric current, coolant flow rate, the cooler's external thermal resistance and the temperature of the ambient air were numerically investigated to evaluate the transient performances of a PEM fuel cell in which the cooling load and cooling ability of its thermal-management system were varied. The results demonstrated that the impacts of the exhaust heat and the cooling conditions on the transient performance of a PEM fuel cell are significant and deserve more attention.