A Unified Preventive Control Approach Considering Voltage Instability and Thermal Overload

This paper presents a unified preventive control approach considering voltage instability and thermal overload. Firstly, a new concept of generalized loading margin (GLM) is proposed. By 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, we discuss the use of a general optimal power flow (OPF), in which the GLM constraints are added. If the GLM of the current system under a given set of contingencies are insufficient, the sensitivity of GLM with respect to control actions is calculated, and a linear programming (LP)-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.