Dynamic Model of a Pressurized SOFC/Gas Turbine Hybrid Power Plant for the Development of Control Concepts

In a situation where fossil energy resources globally run short and the greenhouse effect increases, the interest in new technologies of energy conversion to reduce the demand of primary energy and emission of pollutants grows. The use of high temperature fuel cells like solid oxide fuel cells (SOFCs), especially in combination with gas turbines (GTs), promises remarkable room for improvement in the areas mentioned, compared to other state-of-the-art technologies. But design and handling of such complex plants require efficient control strategies to promote safe and reliable operation. The development of powerful control algorithms is based on an exact knowledge of the operating behavior, which can be obtained using dynamic system models. In this paper a nonlinear model with bulk parameters and 19 dynamic states is presented; the main assumptions and the underlying equations are given. The simulated system consists of a compressor, a SOFC, a turbine, a recuperator, an ejector with a diffusor, a reformer, and a load. Additionally, from the nonlinear model a linear one in state-space representation is derived at nominal conditions. The results of both models are compared. The agreement of the dynamic behavior and of steady state final values is satisfactory. Thus in future studies, methods of linear control theory could be used with the linear model to develop efficient control strategies.