| Long-distance and high-capacity network interconnection may bring power system a higher reliability and efficiency. At the same time, this also allows power system dynamic characteristic and its stability issues become more and more complex. Low frequency oscillations(LFO) at very low frequency range between 0.2 and 2.5 Hz appeared in power system. LFO is a serious threat to the security and stability of the grid and has become a capacity bottleneck of power exchange between transmission lines. As an additional generator excitation control device, Power System Stabilizer (PSS) is seemed as one of the most widely used damping control measure for power system to enhance stability by providing positive damping effectively. As one of basic PSS design issues, PSS parameters optimization in recent year has become a hot issue in LFO research, which has very important practical significance for power system stability improvement. The thesis takes PSS as the study object, and is mainly focused on the optimization issue of PSS parameters.Firstly, the thesis describes the power system small signal stability and basic principle of PSS for LFO inhibition. Through the dynamic time domain simulation, the influence on stability when PSS introduced into the power system is analyzed. At the same time, by using eigenvalue analysis to calculate the small signal stability of power system, the effectiveness of PSS for improving weak-damp electromechanical oscillation modes is also evaluated in frequency domain aspects.In order to make the convention PSS which has traditional lead-lag compensation structure play its damping role effectively, PSS parameters optimization issue is studied in this thesis. To overcome the shortages of standard PSO algorithm, by combining chaos search, an adaptive chaos particle swarm optimization (ACPSO) was proposed, in which the inertia weight of the particle was adjusted adaptively based on the premature convergence degree of the swarm and the fitness of the particle, the diversity of inertia of weight makes a compromise between the global convergence and convergence speed, so it can effectively alleviate the problem of premature convergence. Then ACPSO is used to solve the parameters coordination design of PSS. The numerical example results show that the proposed algorithm has stronger global search capability than PSO, the weak-damp electromechanical oscillation modes are improved significantly, and the power stability is also enhanced. The power system linear mathematical modeling which is lineared at a stable operation point is usually used when solving the PSS parameters optimization issue. This arises ignoration of the nonlinear characteristic influence on system dynamic behavior. Based on ITAE norm, the integrated time and absolute error of all generators speed in power system is taken as the objective function, so it can reduce the difficulty in modeling as well as consider power system nonlinear parts influence on its dynamic performance. The simulation results of four-machine and two-area system show that PSS optimized by ACPSO can effectively increase damping of power system, reduce the overshoots and settling time in system oscillations, finally quell the system oscillation caused by a variety of disturbance quickly.
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