Study On Low-frequency Oscillation Suppression Of Linear Optimal Excitation Control

With the development of power system and the use of fast automatic voltage regulator, the low frequency oscillation has become an outstanding problem. With the interconnecting of national power grids in China, a series of low frequency oscillations even very low-frequency oscillations(0.1~0.2Hz), which destroy system stability,have happened among region power systems. Among these methods to damp the low frequency oscillation, one of the most efficient and economic way is to make the performance of excitation device better, which has been acknowledged generally.This thesis studies the effect of linear optimal excitation controller (LOEC) in damping the low frequency oscillation. The thesis analyses the causation of low frequency oscillations, and establishes the model of a single machine to infinite bus power system using Matlab, which is used to analyse the lag characteristic of excitation system. This paper introduces the design methods of power system stabilizer (PSS) and LOEC, and proves that LOEC has better dynamic performances than PSS through simulation. Two improved arithmetics of LOEC are brought forward, which are LOEC based on pole placement and LOEC based on phase compensation. LOEC based on pole placement uses the complex frequency design of PSS, which can increase the damping of system and improve the stability of power system. LOEC based on phase compensation adds the part of phase leading-lag after the part of feedback, which can satisfy the requirement of phase repair in wider frequency range. Through simulating in time domain,LOEC and two improved arithmetics can damp the low frequency oscillation (0.13Hz) perfectly, which is important to power system.