Robustness of Component Models in Energy System Simulators

During the development of the component-based energy system simulator DNA (Dynamic Network Analysis), several obstacles to easy use of the program have been observed. Some of these have to do with the nature of the program being based on a modelling language, not a graphical user interface (GUI). Others have to do with the interaction between models of the nature of the substances in an energy system (e.g., fuels, air, flue gas), models of the components in a system (e.g., heat exchangers, turbines, pumps), and the solver for the system of equations. This paper proposes that the interaction between models and solvers should be made more robust by making more robust component models which handle the exceptions of the equations inside them, instead of or in addition to trying to remedy these by adding features to the numerical solvers. Improving the robustness of a component model may be more or less difficult depending on the mathematical expressions creating the exceptions. The proposed idea suggests that the solvers may be helped by exception handling leading it back on the right track. The original equation of the model is substituted by an algorithm, so the original equation is only evaluated where it is defined. Outside this region an algorithm is introduced, so the model iterates back to the feasible region. It is shown how this can be done for four different model of energy system component models: turbine constant, gasifier, heat exchanger effectiveness, and heat exchanger heat transfer coefficient.