I. Introduction
The lack of sufficient reactive power in a power system coupled with the continuous increase in load demand are the key factors, among many others, contributing to the occurrence of voltage collapse in modern power systems [1]–[3]. Assimilation of intermittent renewable energy units into the power networks and emerging industrial load centers, which heavily absorb reactive power, has led to a broader and uncertain range of grid operating conditions, including reduced stability margins, especially when optimum coordination is not done [4]. That being so, continuous monitoring and control of power systems through the use of accurate voltage stability indices is urgently needed [3] [5].