Hierarchical cyber–physical defense strategy for integrated electricity–gas systems under attack-induced fault propagation

The increasing coupling between the cyber and physical sides of integrated electricity-gas energy systems enhances the system’s perception and coordinated control capabilities while significantly amplifying its vulnerability to localized attacks. Although numerous studies have focused on improving system defense capabilities, the lack of systematic modeling for the coupling relationship between the cyber and physical layers, coupled with the failure to consider the impact of fault propagation on defense effectiveness, renders these methods inadequate for addressing the complex fault states exhibited by coupled systems following attacks. To address these challenges, this paper first establishes a system operation and fault propagation model for the integrated electricity-gas cyber physical system (IEGCPS). This model comprehensively considers the physical coupling characteristics between the power and natural gas systems, the interaction mechanisms between the cyber and physical layers, and the propagation process of physical faults. On this basis, an integrated cyber-physical attack and defense method is proposed: at the attack level, adversaries coordinate the disconnection of power lines with the disruption of communication links; at the defense level, defenders respond by optimizing the deployment of remote-controlled switches (RCSs) and reinforcing critical communication links. Furthermore, a hierarchical optimization model for IEGCPS is constructed to characterize uncertainties under deliberate attacks, which is solved using the nested column-and-constraint generation (NCCG) algorithm. Finally, simulation studies on the constructed IEGCPS case demonstrate that the proposed method effectively defends against coordinated cyber-physical attacks. Compared with defense strategies that ignore fault propagation, the method in this paper reduces losses by 22.7%.