Nonlinear state space modeling and simulation of a SOFC fuel cell

In order to investigate dynamic behaviors of tubular solid oxide fuel cell (SOFC) and develop a control relevant model for further control studies, a dynamic model based on physical principles is built in the form of nonlinear state-space equation. Dynamics induced by diffusions, inherent impedance, flow, heat exchange and internal reforming/shifting reactions are all considered. Cell temperature, ingredient mole fractions etc. are the state variables and their dynamics are investigated. Dynamic responses of each variable when the external load changes are simulated. Simulation results show that fuel flow, inlet pressure and temperature have significant effects on the dynamics of SOFC. It is further shown that cathode side air inlet temperature has the most direct effect on SOFC performance. Compared with inlet pressures and temperatures, effect of flow velocity is not significant. Simulation also indicates that the transient response of SOFC is mainly controlled by the dynamics of cell temperature owing to its large heat capacity.