A quick method to solve the optimal coordinated voltage control problem based on reduction of system dimensions

•Reducing the search space and speeding up the solving process.•Partitioning the power system immediately after a disturbance.•Dimension reduction of the power system by reducing the number of equations.•Predicting the voltage trajectory based on the two-point method.

This paper presents a new method to speed up the solving process of the optimal coordinated voltage control (OCVC) problem. To this end, after occurrence of a fault, the power system is initially partitioned into interior, boundary and exterior zones by spectral graph partitioning method. Partitioning is based on the fact that voltage instability just after the fault, is a local phenomenon, therefore the variation of boundary and exterior variables is smaller than that of interior ones. Then, the equations of boundary and exterior zones are linearized, the algebraic variables and equations of exterior zone are removed and a considerable decrease in the number of power system equations is obtained which is equal to a reduction in the system dimensions. As a result the determination process of the optimal control actions is fastened. Also, based on the monotonic behavior of long-term voltages, a new method of predicting voltage trajectory is proposed, in which two points are used: the first point referring to the system state just after applying the control actions, which is called jumping point and the final one referring to the steady state of the system. In a case study on the New England 39-bus power system, it was verified that using this method a remarkable increase in calculation speed can be obtained while retaining the system precision.