Damping low-frequency oscillations by tuning the operating point of a dc-segmented ac system

This paper introduces and evaluates a new method for the small-signal stability enhancement of large ac power systems based on segmentation through line-commutated HVDC links. The proposed method is based on the fact that the oscillatory modes of the system may vary by changing the system operating point. In this study, the system operating point is varied by rerouting the flow of power in the ac transmission lines. The flexibility of the HVDC lines in controlling the flow of power in a dc-segmented ac system is used to control the power transmission in the ac lines. An optimization problem is proposed to determine the optimum set-points of the HVDC lines to increase the damping ratio of the underdamped oscillatory modes. Simulation results show that at the optimum operating point, the low-frequency oscillatory modes are damped out significantly and the system net oscillation is less than that of the system at the operating point obtained from a standard economic dispatch. Simulation results also show that there is a trade-off between the generation cost and damping ratio and the proposed method effectively enhances the small-signal stability for a variety of system configurations.