Toward Minimal Number of Controls for Thermal Violation Mitigation for Very Large-Scale Grids

Thermal limit violations in transmission lines should be mitigated as quickly as possible to maintain the system's security and thus entails fast computation of effective control actions. This paper proposes a novel method to rapidly compute ‘minimal’ set of control actions to mitigate the thermal limit violations in large-scale systems and demonstrates the proposed method on a 45,000-bus power grid with a fast speed of 2 seconds. This method is composed of two key stages: Stage 1, extracting a relevant subnetwork from the large-scale system; Stage 2, applying an iterative feasibility check (IFC) method to determine the minimal number of control actions required within the subnetwork. One distinguished feature of this method is its ability to provide high-quality solutions, often achieve global optimality, due to the considerations of both active and reactive AC power flow equations and the corresponding mixed integer nonlinear programing formulations (MINLP). Several computational schemes are developed and integrated into the proposed two-stage method for obtaining the solutions for online applications. Numerical studies on 39-bus, 9,241-bus, and 45,000-bus networks demonstrate the scalability and effectiveness of the proposed online method in handling large-scale power networks. Additionally, the method significantly improves computational speed, achieving thousands of times faster performance (3-digit improvement) as compared to several traditional methods. In addition, the number of control actions needed is minimized, making the proposed method a promising tool for online applications.