Electrochemical parameter identification—An efficient method for fuel cell impedance characterisation

Electrochemical parameter identification (EPI) is a novel, application-oriented characterisation method for fuel cell impedances. EPI strictly works in the time domain, with a model of the fuel cell impedance and measurements of the excitation and the response in the time domain. This approach reduces the measurement time considerably in comparison to frequency domain measurements for electrochemical impedance spectroscopy. The use of a superimposed signal as system excitation leads to less interference of the fuel cell operation than a current interrupt. Short measurement time and little interference enable an online application of the method during the operation of the fuel cell. A simple discrete-time model describing the dynamic electrical behaviour of the fuel cell is depicted as an equivalent circuit which consists of a voltage source and the impedance as internal resistance. The model parameters are identified by a hybrid optimisation algorithm using the sampled excitation and response signals. A comparison of measured impedance spectra at various operation conditions with impedance models identified by EPI shows very good agreement over a wide frequency range and emphasizes the reliability of EPI.