Cyber-physical systems of microgrids and control strategies for enhancing electrical grid resilience

A microgrid can be defined as a group of distribution, generation, storage, and loads. The concept has emerged to utilize renewable energy and increase resiliency of power systems. Modern microgrids rely on sophisticated communication and controls, which require them to interact with cyber-physical systems. In addition, this communication infrastructure is vulnerable to attacks that may potentially bring the whole microgrid system down for seconds to hours. This thesis presents control strategies and approaches for resiliency to attacks against measurements, while increasing system stability, and secure communications within microgrids when microgrids are disconnected from the utility, i.e. in islanded mode, when the frequency of microgrid is thus no longer maintained by the bulk grid. A sequence of operations to continuously serve specific critical loads is discussed. The thesis concludes with a use case that unifies all concepts. This use case serves to mitigate effects of an attack against measurements on a critical load bus. First, the attack is detected by the mean of detection algorithm or by the analysis from the ADVISE model. Then, the preventive algorithm called "reachability analysis" calculates the worst-case probabilistic bounds on whether the unstable states will be reachable within the required time budget. If unstable states are reachable, the command from COM600 will be sent and the suspicious distributed energy resource (DER) will be cut off. The appropriate tie line between two microgrids is closed to continuously supply power to the critical load when consensus from secondary frequency control is reached. Control strategies and communication take action to ensure stability of the new system. Results from real-time simulation validate the effectiveness of our approach