A preventive control model for static voltage stability considering the active power transfer capabilities of weak branches

The voltage instability of power system often occurs when the active power on one or more weak branches exceeds its transfer capability. This paper presents a preventive control model for voltage stability using the active power transfer capabilities of weak branches as static voltage stability margin constraints. A local line-based voltage stability index is used to determine the critical contingencies, weak branches and transfer capability of each weak branch. A static security analysis method, which is based on DC power flow equations, is used to establish the non-linear active power flow expressions on weak branches following each critical contingency. The static voltage stability margin constraints can be obtained from the active power flow expressions and transfer capabilities of weak branches. A quadratic optimal model for preventive control including the proposed static voltage stability margin constraints is presented. The simulation results for the IEEEE14-bus system and IEEE118-bus system demonstrate the correctness and effectiveness of the proposed preventive control model for static voltage stability. Key-Words: Electric power system; Voltage control; Preventive control; Static voltage stability; Weak branches; Quadratic optimal model