System Identification: A New Modelling Approach for SOFC Single Cells

Due to the great number and complex nature of physico-chemical processes, a comprehensive model describing SOFC single cell operation is at present not available. System identification, a modelling approach from control theory is proposed. Instead of infering models from physical laws, the method is based on experimental data to build a mathematical model. Model parameters may subsequently be related to physical processes in the cell. The method is carried to the point of pre-identification of SOFC electrochemical impedance spectroscopy data. A new technique has been developed for calculating the distribution of relaxation times directly from the data. No equivalent circuit has to be assumed. In addition the method yields a higher resolution of dynamical processes than non-linear least squares curve fit. Kramers-Kronig transformation of impedance data was used to calculate the ohmic resistance of the electrolyte and the total polarization resistance of the cell.