Parameter identification and observer-based control for distributed heating systems – the basis for temperature control of solid oxide fuel cell stacks

The control of high-temperature fuel cell stacks is the prerequisite to guarantee maximum efficiency and lifetime under both constant and varying electrical load conditions. Especially, for time-varying electrical load demands, it is necessary to develop novel observer-based control approaches that are robust against parameter uncertainties and disturbances that cannot be modelled a priori. Since we aim at real-time applicability of these control procedures, classical high-dimensional models – which result from a discretization of mathematical descriptions given by the partial differential equations for heat and mass transfer – cannot be applied. Furthermore, these models have to be linked to the electrochemical properties of the fuel cell. To reduce the order of these models to a degree that allows us to use them in real-time, information on both the temperature distribution in the fuel cell stack and the heat flow into its interior due to electrochemical reactions is required. However, a direct temperature measurement is not possible from a practical point of view. For that reason, it is essential to reliably estimate the temperature distribution and the heat flow on the basis of easily available measured data. These data have to be available not only during development stages but also in future series products. For such products, it is desirable to reduce the number of sensors to improve the system's reliability and to decrease the operating costs. The basic strategies that are applicable for model-based open-loop and closed-loop control of heating systems as well as for the identification of parameters, operating conditions and disturbances as well as for state monitoring are summarized in this article. They are demonstrated for exemplary set-ups in both simulation and experiment.