A Lumped Dynamic Modelling Approach for Model-Based Control and Diagnosis of Solid Oxide Fuel Cell System with Anode Off-Gas Recycling

The interest towards anode off-gas recycling (AOGR) in Solid Oxide Fuel Cell (SOFC) systems has recently increased, mainly due to the potential electrical efficiency improvement, as well as to the possibility of avoiding feeding external water for fuel reforming, when adopting such a configuration. However, advanced system control is necessary to ensure such relevant benefits are achieved. Proper control actions and system performance optimization, when AOGR is introduced, entail developing detailed thermodynamic system analysis, in such a way as to remove or at least limit any hazard associated to solid carbon formation, while suitably meeting thermal and electric requirements. To this end, an adequate SOFC stack model is necessary. This work focuses on the identification and validation of an SOFC stack model that accounts for AOGR inclusion. A lumped dynamic modelling approach is adopted to simulate temperature and gas composition at the stack anode outlet. The model is able to simulate the dynamic response of the stack during transients, as shown in Figure 1. Experimental data from a real SOFC system is used in model validation and the modeling approach adopted here ensures achieving a satisfactory compromise between estimation accuracy and computational burden. These factors support using the model as state estimator in model-based control and diagnosis algorithms.

Figure 1 – Comparison between measured and simulated fuel gas temperature at anode outlet