Black-Start Service Restoration of Unbalanced Distribution Systems Considering Frequency Stability Constraints

Power systems are vulnerable to extreme natural events such as hurricanes and floods, which may cause severe blackouts. To reduce the customer outage time and better serve the critical loads, new restoration techniques are required. Accordingly, this paper proposes a black-start restoration model for islanded, unbalanced microgrids by considering the unbalanced operational constraints of DGs. To address the dynamic frequency stability of the system during the restoration process, a transient simulation of the grid-forming DGs was utilized to limit the restored load at each stage of the restoration. Hence, the final model is conveyed in a two-level framework, including a mixed-integer linear programming (MILP) formulation along with a transient simulation model. The proposed method was applied to a modified version of the IEEE 123 node test feeder to study its performance. The results show that the system imbalance can have a significant effect on the total amount of restored load.