Synthesis of A Sequential Stable Decentralized Controller for Flexible A.C. Long Distance Transmission Systems

The use of Static VAR Compensators (SVCs) in long distance transmission systenis is an effective means to damp voltage fluctuations and to improve the system stability, both under small and large disturbances. Additional advantages can be obtained by adopting Thyristor Controlled Phase Sliiftcrs (TCPSs) able to regulate the active power flow, to reduce the power arid frequency dcviations atid lo increase the transmission system capacity. The control actions ol these compoments must be co-ordinated with a control strategy associated to synchronous In this paper, a systernatic procedure for the co- ordinated design of decentralized controllers associated to the generating units and the TCPSs at the sending end, as well as to all the SVCs distributed at intermediate substations of an A.C. long distance transmission system, has been developed. The proposed procedure is organized in two steps. The sequential design of the controllers associated to the Pf and QV channels allows to drive oscillatory arid aperiodic modes in a selective way. Additionally, sequential stability is assured at each step of the procedure. An example is presented to illustrate the validity and usefulness of the suggested approach.