The proposed research focuses on cascading failures in electrical energy cyber-physical systems (CPS), which is a critical infrastructure of our nation. Cascading failures, where the failure of one or few components causes a wide-spread failure of the interconnected system, is a major cause of blackouts in power grids. The mechanism of such failures is highly complex as it involves the physical layer of the grid (e.g. generators, transmission lines, etc.) and the cyber layer (e.g. communication and control elements) in a coupled manner. This is a very important problem to investigate as cascading failures can cost our economy billions of dollars. This project takes a holistic view at taming cascading failures in electrical energy CPS. The proposed research has two tightly coupled thrust areas. Thrust 1 aims at an accurate understanding of the cascading failure mechanism and its prevention, while Thrust 2 focuses on recovery following blackouts under uncertainty of failure locations. Theory of trajectory sensitivity and graph theory are leveraged to develop a fundamental understanding of cascading failures in energy CPS, which can be applied to other CPSs where the physical system is dynamic in nature and the failure propagation in the physical system and the cyber system are coupled. The proposed preventive control strategy can protect critical infrastructures from large-scale failures and facilitate higher resiliency, whereas the proposed recovery strategy is applicable in the aftermath of a blackout caused by cascades, natural disasters, or other events, which will reduce downtime of the critical infrastructure. In support of the Broadening Participation in Computing initiative among women, the proposed research will be integrated into the one-week summer camps offered by the School of EECS at Penn State. Presentations about this research will be given to high school girls over the course of one week in the 2019 camps, and then camps focused on curriculum on the topic of this research will be offered in 2020 and 2021.

The proposed research has two key objectives (a) develop an accurate understanding of the cascading failure mechanism and its prevention, and (b) develop a recovery plan following blackouts under uncertainty of failure locations and budget constraints. The quasi-steady-state (QSS) model of power grid used in literature for studying cascade propagation produces inaccurate results towards the later stages of blackouts, whereas a fully dynamic model is impractical for large-scale statistical analyses. To solve this, a 'temporally hybrid' and a 'spatio-temporally hybrid' model are proposed, which quantify the stress of the grid at the systems level and the component level, respectively, using trajectory sensitivity theory, and appropriately switch from the QSS to the dynamic model. Next, a unified graph-based model for interdependent power grid and communication systems is developed, which takes into account several special features of the legacy Supervisory Control and Data Acquisition (SCADA) system along with the modern Wide-Area Monitoring, Protection, and Controls (WAMPAC) system, and the observability and controllability they provide for the CPS. Furthermore, a stability-constrained remedial action scheme for cascade prevention is proposed. Finally, a new approach for progressive assessment and recovery, which leverages the hybrid power grid models and the unified communication network model, is proposed in the presence of budget constraints and failure uncertainties.