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Impact of DG Connection Topology on the Stability of Inverter-Based Microgrids

In this letter, we theoretically explain that the common connection topology for inverter-based distributed generators (DGs) is harmful to the small-disturbance stability of microgrids. We first prove that the algebraic connectivity of a graph will approach zero in case of inappropriate expansion of nodes and lines. Such type of expansion is often the case in microgrids where new DGs are simply connected to the nearby nodes via single lines that leads to a tree-like structure. Furthermore, we prove that the zero algebraic connectivity leads to a zero eigenvalue in the dynamic Jacobian matrix of microgrids and, hence, deteriorates stability. The result reveals the importance of careful planning for DG connection topology especially when a large number of DGs are to be integrated. It also suggests that forming loops by linking the nodes close to feeder terminals could be an effective way for stability enhancement.