Interconnected Autonomous AC Microgrids via Back-to-Back Converters&x2014;Part I: Small-Signal Modeling

In this article, a set of autonomous ac microgrids, interconnected by back-to-back converters, is taken into account, where they are supplied fully using voltage source converter-based distributed energy resources. A comprehensive and generalized small-signal model of the interconnected autonomous microgrids as a large-scale system is proposed using the interconnection method. The modeling is based on detailed module models to show the impact of each module on the dynamic modes, especially the dominant critical modes. It is generalized and scalable due to separate modeling of modules as well as using unlimited and expandable interconnecting. The proposed interconnection method deals with all electrical and control connections between individual modules including feedback, feed-forward, augmentation, and the order of module inputs and outputs. The model is validated employing Prony analysis method and using output results of an OPAL-RT real-time simulator. Using the proposed modeling method, the small-signal stability analysis and controller design can be realized simply for interconnected microgrids with any number of microgrids and different structures. Typically, for two interconnected microgrids, all dynamic modes and participant state variables in different frequency ranges are identified using the eigenvalue analysis and participation matrix in MATLAB.