STRONG CONTROLLABILITY AND OBSERVABILITY AND THEIR EFFECTS ON TRANSIENT STABILITY OF POWER-SYSTEMS

An algorithm is developed for identifying bus clusters called control areas that have strong local controllability and observability propert y for measurements and controls at the buses or on generators within t he control area. Two types of control areas are identified; one that i s based on weak boundaries of the reactive power voltage jacobian and is called voltage control area; the other is based on the jacobian of both real and reactive power balance equations with respect to voltage and angle at network buses. The two control areas are identical under light load conditions, but are different as the system approaches vol tage collapse or poorly damped low frequency oscillations. The underst anding of strong controllability and observability in terms of real po wer angle dynamics and reactive power voltage dynamics (voltage contro l areas) and the strong controllability and observability of voltage a nd angle dynamics (control areas) helps understanding of voltage insta bility and inter-area oscillations.