Smooth plug-and-play of distributed generators in islanded microgrids via dynamic secondary control and mode transition

A smooth plug-and-play (PnP) strategy is proposed for distributed generators (DGs) in islanded microgrids to mitigate the transient power imbalance and the resulting frequency and voltage deviations during DG connection and disconnection. The strategy is developed within a conventional hierarchical control framework and introduces dynamic control gains and power distribution coefficients to achieve smooth power redistribution. For DG disconnection, a coordinated grid-forming (GFM)-to-grid-following (GFL) mode transition is further introduced to reduce the DG output power to zero, with the transition timing determined using both model-based and data-driven methods. The strategy can be implemented under centralized or distributed communication architectures. Experimental results on a physical microgrid platform demonstrate that the proposed method effectively suppresses PnP-induced transient disturbances while preserving the frequency restoration and power sharing functions of the conventional secondary control framework.