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

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... 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. A Modelica-based solution for the simulation and optimization of microgrids 42 Figure 10 . Three phase microgrid system implemented using Electric Power Library components. It is composed of 4 units: an ideal DC source controlled in PQ mode to represent a renewable energy source, a diesel engine, an ideal impedance load and an AC voltage source to represent the main grid. The microgrid is first operated in islanded mode. At t=2 s, the synchronization process is initiated, and synchronization occurs after 200ms. A load change occurs at t = 3.5 s. At t =5 s, the microgrid is suddenly disconnected from the grid and the diesel engine reacts to maintain the internal frequency and voltage levels.