Power system stability enhancement employing controllers based on a versatile modeling

Abstract

Rapid advances in power electronics have made it both practicable and economic to design powerful thyristor-controlled devices, such as Flexible AC Transmission Systems (FACTS), for stability enhancements. The discrepancies of existing modeling approaches have limited the feasibility of handling these devices or designing its damping controller. In this thesis, a versatile and generalized approach to model standard power system components is proposed. The more systematic and realistic representation, accompanied by the development of powerful eigenvalue-analysis techniques, facilitates the study of small signal stability (monotonic and oscillatory) of the power systems. In monotonic stability study, the effect of exciter and governor is critically reviewed based on the exploitation of eigenvalues, modal and sensitivity analyses over a wide range of operating conditions. In oscillatory stability study, a common FACTS device, the static var compensator (SVC), is used to improve system damping. This study reveals the inadequacy of many conventional methodologies in SVC design since they have ignored (or cannot handle) some important factors such as SVC mode instability and robustness of the power system. Two approaches, combined sensitivities and H∞ algorithms, are introduced to solve these limitations. Finally, an extended H∞ algorithm, which is applied to PSS design and successfully solves certain limitations of the existing H∞ based PSS design, is also presented. Although these studies are developed on selected controller devices or typical systems for convenience of discussion, extension to more complex systems can be dealt with in a similar way because of the versatility of the proposed modeling methodology.