Flexible alternatives to decoupled load flows at minimal computational costs

Abstract

In this paper, we propose two useful load flow algorithms called the enhanced decoupled load flow and the simplified Newton–Raphson load flow. They are obtained from the expression of the full Newton–Raphson load flow method by successively diminishing the effects of the off-diagonal submatrices in the Jacobian. In the process of simplification, we use the Neumann series expansion. Their potential use can be the flexible alternatives to the decoupled load flow (DCL) methods that totally ignore the effects of the off-diagonal submatrices in the Jacobian. The proposed load flow methods converge significantly faster and are more stable than the conventional fully DCL which updates the Jacobian submatrices in each iteration. In our test with 733-bus systems, they converge even when the fast decoupled load flow (FDL) and its variations keeping load flow matrices constant experience convergence problems. The proposed load flow methods can improve the convergence characteristics particularly when the P– Q coupling becomes significant and the power system operating states deviate from the conditions required for stable convergence of the FDL and the DCL by reflecting in part the effects of the off-diagonal terms in the Jacobian. Test results show promising performances of the proposed algorithms in their convergence characteristics both in number of iterations and overall convergence speeds.