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This paper proposes and investigates a new line-commutated current-sourced converter (LCC)-high voltage dc current (HVDC) global supplementary control (GSC) strategy for stabilizing and enhancing the dynamic performance of a large ac system that is segmented by LCC-HVDC links. The GSC is designed based on a linear quadratic Gaussian (LQG) method and enables coordinated supplementary control action of multiple HVDC links that participate in segmentation. The GSC can stabilize the ac system while either minimizing the propagation of oscillatory dynamics from one segment to other segments (GSC1) or enabling their controlled transfer from a disturbed segment to other segments (GSC2). The study results show that in a fully-dc-segmented system: 1) GSC1 and GSC2 are able to stabilize the system; 2) under GSC1, each segment can experience major disturbances without causing adjacent segments to experience the disturbances with the same degree of severity; and 3) GSC2 enables controlled transfer of the oscillations among the segments and, depending on the system configuration, can further reduce the magnitude and duration of oscillatory dynamics. The studies are conducted on a three-segment ac system including three interconnecting LCC-HVDC links. [ABSTRACT FROM AUTHOR]

Hopf bifurcation phenomenon of a power system results in oscillatory dynamics which can lead to instabilities in the system. Therefore, it is desirable to operate the system such that a sufficient margin to Hopf bifurcation is ensured. This paper presents a methodology based on the adjustment of the setpoint values of the HVDC link controllers, to prevent instability or increase the stability margin of the system subject to Hopf bifurcation. In this paper, the first-order sensitivities of the Hopf stability margin to the setpoint values of the HVDC links are presented. These sensitivities identify the optimum direction to change the HVDC setpoints to steer the system away from instability, increase the stability margin, and improve the damping of oscillatory modes. The proposed method is evaluated on various system configurations subject to Hopf bifurcation phenomena caused by a variety of events, such as load and line impedance variations. Simulation results show that at the optimum operating point, for a variety of Hopf bifurcations, the stability margin and damping of the oscillatory modes improve. [ABSTRACT FROM AUTHOR]