Mitigation strategies to absorb impacts from extreme events that may trigger cascading outages are crucial for modern power systems, particularly given the increasing penetration of power electronics, thereby enhancing system resilience. This paper presents a comprehensive resilience-centered framework that integrates cyber-physical cascading mitigation through network topology reinforcement and operational strategies, specifically DC segmentation and controlled islanding, respectively. The methodology first identifies AC lines at segmentation boundaries (i.e., those that most frequently contribute to system partitioning) and evaluates the benefits of replacing them with VSC-HVDC links through dynamic cascading analysis and quantification, thereby enabling the asynchronous interconnection of segments. This approach helps confine cascading impacts within segments, significantly reducing the risk of widespread blackouts, especially in renewable-rich power grids with a heightened risk of instability. Next, to enhance operational resilience against cascading failures, controlled islanding is implemented within the DC-segmented system undergoing cascade initiation, effectively further confining cascading stress to a limited area around the origin of the initiating events. Tailored to enhance resilience in hybrid AC/DC power grids against cyber and physical cascade triggering events, the method leverages a cyber-anomaly detection technique to identify elements affected by fabricated protection trip commands and measurement replay attacks, distinguishing cyberattacks from physical disturbances. Implemented in the IEEE 39-bus and 118-bus test systems with dynamic cascading failure modeling that fully captures voltage and frequency transients in system response, the method demonstrates improvements of up to 88 % and 97 % in served demand, respectively, highlighting its effectiveness in mitigating cascading impacts and enhancing system resilience.

Cyber-physical power systems are susceptible to cyber threats and attacks that can lead to cascading failures and widespread power outages. Therefore, mitigating the impact of such attacks requires the timely implementation of operational strategies to prevent cascading blackouts. One Such strategy is the controlled islanding of the affected power grid, serving as a last resort against the propagation of the cascading outages. In this context, this paper introduces a novel detection-informed operational mitigation strategy, i.e., controlled islanding, against cyberattack-induced cascading failures, addressing 'when' and 'where' to implement controlled islanding. The proposed strategy leverages dynamic cascading failure modeling to quantify the impact of ongoing cyberattacks on power grids, using quantitative metrics such as demand-not-served (DNS). For effective operational mitigation, the strategy initiates controlled islanding when any attack, including fabricated protection trip commands and measurements' replay attacks, are detected, and any operating limits, such as line loading, are violated. It then proceeds to the implementation of controlled islanding, where identified cyberattack-affected elements are effectively surrounded by stable and self-sufficient islanded areas, while minimizing the system DNS. Numerical results on the IEEE 39-bus system demonstrate the effectiveness of the proposed strategy, reducing the DNS value by up to 47% when the controlled islanding strategy is implemented.