Voltage stability analysis of electric power systems with frequency dependent loads

During the last decade great attention has been devoted in the technical literature to voltage stability problems of interconnected power systems. However, power system operators have found that voltage collapses often occur in a real system at a load condition different from the one predicted by simulation studies. One of the causes that makes the use of present approaches unreliable is the lack of adequate models for static loads, which are traditionally represented by constant power or, generally, by voltage dependent characteristics. To overcome this difficulty, the paper proposes a new and practical procedure for analysing the effects of static load modelling on the voltage stability limit of power systems. To this purpose an accurate model for static loads is used which takes into account their frequency dependence. This is very important to avoid unacceptable inaccuracies in determining the actual voltage stability limits of heavily loaded and isolated power systems. Two numerical examples illustrate the capability and usefulness of the proposed technique.