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This paper describes the development of an optimization-friendly thermodynamic property model of water and steam that covers liquid, vapor, 2-phase as well as the super-critical region. All equations are at least twice continuously differentiable with respect to all model variables and can be used in dynamic optimization problems solved by efficient derivativebased algorithms. The accuracy has been verified against the industry standard IAPWS IF97 and performance and robustness have been tested by solving a trajectory optimization problem where the start-up time of a gas power plant has been minimized while satisfying constraints on temperature gradients, pressure and flows. Simulations of various plant models have also been performed to verify and benchmark the implementation. The results show that the new media can be used in both solving dynamic optimization and simulation problems yielding reliable results. The new media has been integrated into Modelon's Thermal Power library 1.13. This article is built upon the work in (Åberg, 2016).

By integrating a high share of distributed generation units, microgrids can accelerate the shift to a more sustainable power grid. This transition is however not free from challenges. The variability and uncertainty of the renewable energy sources as well as the absence of large-scale dispatchable storage systems pose challenges for the integration and operation of this new type of power grid. Model-based engineering can provide valuable tools to develop design and control strategies that do not jeopardize the stability and reliability of the power supply. This paper presents elements of a Modelica-based workflow for the design and operation of microgrids. The framework allows for a multi-fidelity modeling approach and is therefore suitable for solving a large variety of engineering problems, from early component design to the verification of component and control design using detailed models. This paper illustrates the flexibility of the framework with respect to the user interface, the models and the analyses.