Cyber-Physical Design and Implementation of Service Restoration Framework for Islanded Power Systems

Cyber-physical energy systems with high penetration of distributed energy resources provide several grid support functions including black-start in islanded mode. In an inverter dominated power system, both grid-forming (GFM) and grid-following (GFL) inverters have a role to play in regulating system frequency/voltage and maintaining proportional power sharing through grid support functions. A self-sufficient power system can restore critical loads by forming microgrids (MGs) around black-start distributed generators (DGs). This work proposes a service restoration framework that adopts GFM inverters as black-start units and achieves load restoration in the context of dynamic MGs with automatic sectionalization and network reconfiguration. The proposed approach is structured as a two-layer framework consisting of an optimization and power systems simulation layer. Mathematical optimization models can only solve for the steady-state power equations. However, the associated dynamic transient response can cause instability in a weak power grid. Therefore, the optimization layer explicitly incorporates dynamic stability constraints developed from the power systems simulation layer. An optimal network reconfiguration sequence and power reference commands for DGs are generated during the restoration process. Moreover, a consensus based multi-agent distributed control is designed for coordination among GFM and GFL inverters. The approach is validated over a modified IEEE-123 node test feeder using real-time controller-in-the-loop simulation with OPAL-RT simulator.