Fractional Order System Identification Method for Online Monitoring of Humidity of Electrochemical Hydrogen Pumps

electrochemical hydrogen pump (EHP) is a promising technology capable of extracting hydrogen from miscellaneous gas mixture and compresses it to very high pressures. The basic working principles are similar to that of a proton exchange membrane (PEM) fuel cell. Consequently, its performance is heavily dependent on humidity level of the membrane. Unlike PEM fuel cells where water is generated as a by-product, in the case of EHP the humidity has to be delivered via external humidifier. Therefore, it is paramount to have accurate information regarding the humidity in order to achieve optimal exploitation. Inaccessibility of the membranes makes it almost impossible to perform direct humidity measurements. Addressing this issue, this paper presents a method for online estimation of humidity levels based on the parameters of an equivalent circuit model (ECM). The parameter estimation is performed through a combination of evolutionary algorithm and simplex optimization. The method is evaluated on a market ready EHP device with capacity of pumping 1.4118 stl/min of H₂.