Dynamic Characteristics of PEM Fuel Cells

Fuel cell applications have become increasingly attractive. Therefore, comprehensive models, simulation and analysis tools are required to characterize fuel cell behavior. For years, the focus has been on describing the steady state characteristics of fuel cells, which is an important application but certainly not the only one. This paper presents methods to measure steady state and transient behavior of polymer electrolyte membrane fuel cells (PEMFC). An active load that enables all required measurements is described. Furthermore, a simple large-signal dynamic PEM fuel cell model is introduced of which the parameters can be found with an interrupted current method. This method estimates the parameters of the dynamic model. However, there was doubt whether the influence of small-signal disturbances in the fuel cell operation could be analyzed with the interrupted current method. Therefore, impedance spectroscopy measurements were performed on the fuel cell stack to determine if the large-scale model was applicable to small-signal excitations. Practical measurements show that an additional small-signal model should be introduced to characterize a fuel cell stack when switching ripple is present in the output current