Approaches to Obtain Usable Solutions for Infeasible Security-Constrained Optimal Power Flow Problems Due to Conflicting Contingencies

Satisfying the N-1 security criterion, a requirement in power system operation, is not always possible in practice, particularly under stressed operation conditions (e.g. heavy loading), unexpected renewable generation output or unavailability of effective control actions. Under such circumstances, in the presence of conflicting contingencies, the deterministic AC security-constrained optimal power flow problem, which computes the optimal mix of preventive and corrective actions to enforce N-1 security, may be infeasible and hence its computations diverge. In such a case, the transmission system operator absolutely needs a usable solution which minimizes in some manner the degree of problem infeasibility or the risk of operation insecurity. To tackle this important and challenging issue, severely under-addressed so far, this paper explores different candidate approaches, which are based on relaxing either the set of control variables or operation constraints. The pros and cons of the explored approaches are analyzed using the IEEE 118-bus system.