Analysis of ill-conditioned power-flow problems using voltage stability methodology

Abstract

Ill-conditioned power-flow problems have been widely investigated and reported in the literatun:. A typical approach develops enhanced solution algorithms when a power-flow case is found divergent with the conventional Newton method. It is known that a genuine ill-conditioned problem is caused by the presence of a large condition number in the power-flow Jacobian matrix. Since a large condition number is associated with small singular values or eigenvalues of a matrix and the voltage collapse is also related to small eigenvalues, it is therefore postulated that an ill- conditioned power-flow problem is actually a voltage collapse problem. The objective of ths paper is to investigate the relationship between power-flow ill-conditioning and voltage instability. The findings confirm that power-flow ill-conditioning only occurs at the voltage collapse point. As a result, developing improved algorithms to solve the problem is an unprofitable strategy. The well- known voltage stability assessment techniques such as the PV curve method are sufficient for the problem. This conclusion is supported with case studies on five widely known ill-conditioned power- flow problems and rigorous mathematical analysis.