Possible Implications of Using Dynamic Equivalent Models in the Design of Controllers to Damp Inter-area Oscillations

This paper studies the adequacy of a dynamic equivalent method for applications in the design of damping controllers for an inter-area mode of a large-scale power system. This study was carried out as part of the development of the future Paraguayan-Argentinean-Uruguayan interconnected system. The designed controller was a power oscillation damper of a STATCOM that will be enabled as a backup to damp an inter-area oscillation predicted to appear once the interconnection is completed. A dynamic equivalent model was developed using an approach based on generator coherency identification, while the controller was designed by a pole placement method based on the damped Nyquist plot. Although the designed controller shows satisfactory results for the equivalent model used to design it, when tested in the large-scale detailed model of the system it fails to ensure the desired small-signal stability margin. This result is presented and its implications are discussed from the viewpoint of Hardware-in-the-Loop testing of damping controllers for bulk power systems.