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 instal led. This paper presents a coordinated control scheme for excitation system s and TCSC controls for improving the stability of a transmission system, w here a power plant is connected with a power grid through long transmission lines. Based on the TCSC equivalent reactance and the modulated active pow er, a control law for the TCSC is deduced associated with the control law o f the excitation system on nonlinear basis. The proposed control scheme is developed upon nonlinear optimal-variable-aim strategies (OVAS). With two p re-selected aims to be achieved during first swings following a fault and i n sequent dynamic ranges, coordinated actions of the TCSC and excitation sy stem can be an effective means of enhancing transient stability and damping subsequent oscillations. The effectiveness and robustness of OVAS-based co ntrols are demonstrated with a one-machine system, where the simulations ar e carried out by the NETOMAC program system. In comparison with a conventio nal control scheme, significant improvements in dynamic performance of the test system are achieved by the proposed control strategy. (C) 2001 Elsevie r Science B.V. All rights reserved.