Variable Structure Approaches for Temperature Control of Solid Oxide Fuel Cell Stacks

Fuel cell systems are promising devices for an efficient decentralized supply with electricity and process heat. However, such power supply systems are typically characterized by a dominant non-stationary behavior because of small grid sizes with variable power demands. In addition, storage and load shaping devices — such as battery systems — have to be kept as small as possible to guarantee cost effectiveness. Due to non-stationary operating conditions, it is necessary to develop nonlinear control strategies to ensure high efficiency and to guarantee robustness against a-priori unknown load variations. In previous work, fundamental control procedures have been developed which comprise ideas of sliding mode and model-predictive control. The sliding mode strategies are extended in this paper towards higher-dimensional system models, resulting from a finite volume representation of the thermodynamics of solid oxide fuel cell stacks (SOFC stacks). Simulations and preliminary experimental results are presented to highlight the corresponding design procedures and their practical applicability.