Improved general purpose fast decoupled load flow

Abstract

This paper describes a simple method for strengthening the decoupling of real and reactive powers that leads to an improved general purpose version of the state-of-the-art approach for fast decoupled load flow solution due to Stott and Alsac. The basic idea is to solve suitably combined real and reactive power equations rather than considering them independently. Simple multiplying factors are derived for combining the equations for real and reactive powers such that the combined equations are insensitive to variations in bus voltage magnitudes/angles. These combined set of equations are linearised to obtain the final decoupled model. Based on the assumption of uniform R/ X ratios for all branches, further simplified load flow model with symmetrical coefficient matrices is also developed. Both these models are tested on various standard and IEEE test systems and also on a typical Indian radial distribution system. These investigations, carried out with uniformly, non-uniformly and randomly scaled resistances or reactances for simulating the effect of high R/ X ratios, indicate better or equal convergence characteristics of the proposed methods in comparison with the other fast decoupled load flow approaches reported in the literature.