Stabilization of an AC-DC power system using a controlled multiterminal HVDC link

A state space formulation of an integrated 3-area AC-DC power system operating with a 3-terminal HVDC link is presented. The chosen power system, which is marginally unstable, can be stabilized by modulating the power orders of one of the converter stations by using signals proportional to the speed and tie-line power deviations and their derivatives. The signals are chosen in such a way that the dominant modes of the system can be shifted to prescribed locations to ensure greater damping within the practical gain constraints of the controllers. It is also shown that excellent dynamic performance can be obtained by a combination of modal output feedback control for one converter station and power-order modulation of other stations using the signals of individual areas. A 3-area 3-terminal HVDC-AC system has been considered for digital simulation and the results demonstrate the damping effect of multiterminal HVDC links when controlled by suitable signals derived from the AC system.