Unified preventive control approach considering voltage instability and thermal overload

Unified preventive control approach considering voltage instability and thermal overload is discussed. First, a new concept of generalised loading margin (GLM) is proposed. Using GLM, contingency and load increase scenario are represented using a unified parameter, and the unsolvable contingencies are treated the same as the solvable contingencies. Then, The use of a general optimal power flow (OPF) in which the GLM constraints are added is discussed. If the GLM of the current system under a given set of contingencies is insufficient, the sensitivity of the GLM with respect to control actions is calculated, and a linear programming-based OPF algorithm is performed to determine the preventive control strategy. Several algorithms including a two-step method to calculate GLM are proposed to improve the calculation speed. Among the possible controls, emphasis is put on generation rescheduling and load shedding. Case studies are presented on a real 682 bus system. The results prove that this method is efficient.