Direct methods for studying dynamics of large-scale electric power systems—A survey

This paper attempts to give a unified overview of how direct methods solve the transient stability problem of large-scale power systems. Two distinct methodologies are considered and discussed. The first concerns application of the direct Lyapunov method to the conventional transient stability analysis. Both scalar and vector Lyapunov approaches are envisaged and their respective merits and potentialities are compared. Particular attention is also paid to the estimation of ‘practical’ stability domains, aiming to overcome the usual conservativeness of the Lyapunov criterion. The second methodology focuses on the derivation of stability indices, intended for on-line monitoring, contingency evaluation and security control. The present achievements and future trends are explored and tentatively assessed.