Grid-Aware Islanding and Resynchronisation of AC/DC Microgrids

This paper proposes an optimal, grid-aware supervisory control framework for the islanding, islanded operation, and resynchronisation of hybrid AC/DC microgrids. The framework relies on a unified hybrid AC/DC power flow (PF) model that explicitly represents the grid-forming operation of AC/DC interfacing converters (ICs). Sensitivity coefficients (SCs) are derived from this model and used to formulate the voltage and branch-current constraints of the optimal power flow (OPF). The considered operating mode is relevant for hybrid microgrids that aggregate DC-native or DC-interfaced resources, such as photovoltaic units, batteries, and electric vehicles, through a DC network. During islanded operation, the grid-forming IC regulates the AC voltage and frequency, while the active-power balance is supplied through the DC grid. This separates the active- and reactive-power slack locations and requires a dedicated PF and SC formulation. The proposed OPF computes the optimal setpoints that satisfy voltage and ampacity constraints before, during, and after the islanding manoeuvre, while local converter controls ensure voltage and frequency regulation in real time. The proposed framework is experimentally validated on a 27-node hybrid AC/DC network with three ICs and a mix of controllable and stochastic resources.