A tri-level optimal defense method against coordinated cyber-physical attacks considering full substation topology

In recent years, power systems have been facing an increasing risk of malicious attacks. As modern power sys-tems have a greater reliance on communication and automatic control systems, coordinated cyber-physical at-tacks will cause more serious consequences for the reliable power supply than traditional malicious attacks. To enhance the resilience of power systems against coordinated attacks, a defense method to allocating hardening resources is proposed in this paper considering the full substation topology and the multi-stage response process of power systems. The problem is formulated as a tri-level optimization model involving interactions among the defender, the attacker, and the operator, in which the synergy impact of three attack forms is considered, i.e., physical attacks causing short-circuiting, cyber attacks causing protective relay misoperation, and cyber attacks causing protective relay maloperation. A graph-based analytical model is established to characterize the impact process of such coordinated attacks on power systems. Case studies are conducted on the IEEE RTS 24-bus system. The influence mechanism of coordinated cyber-physical attacks involving protective relays on power systems is systematically revealed. Results show that the proposed method can effectively defend against the above-mentioned coordinated attacks, and enhance the resilience level of power systems. In addition, a sensi-tivity analysis is implemented on the influence of attack resources and defense resources on the unserved energy at each stage of the system.