Mitigating Cascading Failures by Enhancing N-2 Security Using a Unified Preventive-Corrective Generation Rescheduling Approach

Although the N-1 criterion is widely applied, cascading failures and large-scale blackouts still occur in power systems. Thus, incorporating N-k (k > 1) security constraints in the Security-Constrained Optimal Power Flow (SCOPF) problem is essential, with N-2 contingencies being the most probable cause of cascading failures. However, modeling all N-2 contingencies increases the number of constraints, resulting in excessive computational burden. To address this, we propose a statistical constraint screening method that reduces the number of N-2 constraints by 75%, from 19,108 to 4,744, significantly decreasing problem size. Additionally, a closed-form LODF-based formulation is developed to evaluate N-2 post-contingency flows without network topology reconstruction. Two optimization models-separate and unified-are proposed and compared for generation rescheduling in SCOPF. Simulation results on the IEEE 39-bus system demonstrate that the unified model reduces the total preventive action cost (PAC) by up to 7,417 $/h and decreases computational time by 32%, while ensuring complete N-2 contingency security.