  Accurate real-time assessment of power systems voltage stability has been an
active area of research in the past few decades. In the past decade, after the
development of phasor measurement units (PMU), a lot of discussions has been
going on phasor measurement techniques for real-time voltage stability. The
fundamental idea behind these methods is to find the Thevenin equivalents of
the system, and then determine the voltage stability margin based on the
equivalent circuits. Some approaches also include the use of Artificial Neural
Networks (ANN), for online monitoring of voltage stability margins. These
methods are really fast as compared to the other methods. It has been shown
that if we can obtain the phase angles and voltage magnitude in real-time from
the phasor measurement units (PMU), then the voltage stability margins can be
obtained in real-time and we can initiate voltage stability control methods. We
are going to discuss Thevenin's equivalent methods and Artificial Intelligence
methods in detail in this paper. We will also introduce the traditional methods
which were earlier used for power systems stability assessment such as Time
Domain methods, Static Methods, and Sensitivity methods. We are going to
finally compare these methods and try to give general guidance on choosing a
power stability method.
