A nonlinear control for coordinating: TCSC and generator excitation to enhance the transient stability of long transmission systems

The transient stability of a long transmission system can be significantly influenced by the action of excitation systems and any TCSC controls installed. This paper presents a coordinated control scheme for excitation systems and TCSC controls for improving the stability of a transmission system, where a power plant is connected with a power grid through long transmission lines. Based on the TCSC equivalent reactance and the modulated active power, a control law for the TCSC is deduced associated with the control law of the excitation system on nonlinear basis. The proposed control scheme is developed upon nonlinear optimal-variable-aim strategies (OVAS). With two pre-selected aims to be achieved during first swings following a fault and in sequent dynamic ranges, coordinated actions of the TCSC and excitation system can be an effective means of enhancing transient stability and damping subsequent oscillations. The effectiveness and robustness of OVAS-based controls are demonstrated with a one-machine system, where the simulations are carried out by the NETOMAC program system. In comparison with a conventional control scheme, significant improvements in dynamic performance of the test system are achieved by the proposed control strategy. (C) 2001 Elsevier Science B.V. All rights reserved.