Fast Computation and Stable Convergence Technique for Unbalanced Load Flow Calculation in the Large Scale System

Abstract

This paper presents a new method of unbalanced load flow calculation to improve complexity by the method of advanced symmetrical coordinates. Usually, the electric power system has been calculated only by positive phase sequence component on the assumption that three phase transmission lines and loads are balanced. However, many ultra high voltage transmission lines are not transposed, therefore mutual inductances cause negative sequence current in trunk transmission system. Negative sequence current causes the heating of the generators and transformers. Therefore, the three phase sequence component should be calculated accurately.We examined fast computation and good convergence performance of unbalanced load flow calculation by the models of three phase transmission lines, transformers and loads. The proposed method is not the phase coordinate system but the method of symmetrical coordinates. This technique decreases numerical complexity by the use of simplified jacobian matrix. The convergence performance of this method is inferior to usual Newton-Raphson method. In consequence, the problem of poor convergence performance is improved by the technique for newly developed deceleration Newton method.