| One of the most important stability problems in electric power system operation is the steady-state stability, or in control terminology, the small-signal stability around a system operating point. Oscillations of small magnitude and low frequency, linked with the electromechanical modes in power systems, often persist for long period of time and in some cases present limitations on the power transfer capability. Power System Stabilizer (P55) units have long been considered as an effective way to enhance the damping of ElectroMechanical Oscillations (EMO) in power systems. The conventional P55 was first proposed in 1960's and classical control theory, described in transfer functions, was used for its design. Linearised models can be used for their study and a conventional P55 can be considered as a Single-Input Single- Output (5180) feedback controller installed on a generation set. One of the three signals, machine shaft speed, AC bus frequency or accelerating power can be used as input to a conventional PSS. Of these, the most commonly used is the machine shaft speed. The output of PSS is a supplementary control signal and applied to the machine voltage terminal. Robust stability of power systems must be ensured within a large scale of operation. In this paper, a newly proposed PS de.ign inethudi, H-~pt馳ti7nttoft method, is applied to make a fixed-structure and fixed-parameter P55 (HPSS) design. Compared with the adaptive control method, the parameters designed by H optimization method are invariable with the operation condition, but HPSS still has the capability to guarantee the robust stability of the systems. Some research on applying H optimization method to P55 design is also presented in some publications, but the importance and difficulties in the selection of weighting functions are reported. The system studied in these publications were restricted to single-machine infinite-bus power systems. The main work contributed by this paper is as follows. (1) A new method of selection of weighting functions in H_∞, optimization design is proposed.. (2) The selected weighting functions are applied to PSS design for a single-machine infinite-bus power systems to verify the robust stability in a large area of operating conditions. North China University of Electric Power Master's Thesis (3) The optimal installing position is decided which aims to damp a specified negative damped or poorly damped EMO by calculating the generator participating factors and analyzing the related characteristics between each machine and the close loop poles. (4) According the principle of sequential loop closure, the H0. optimization method using the proposed selected weighing functions is applied to a multi-machine system. Satisfactory damping results are obtained. Analysis in frequency domain and calculation in time domain simulation demonstrated that the proposed H0. optimization P88 design for multi-machine power systems has many advantages over the traditional design methods in its simplification, damping effects and robust stability. In fact, each design method has its own merits and shortcomings. The focus of this paper is, therefore, on solving some difficulties in applying H0. method to multi- machine system PSS design, and on exploring its potentials and limitations. As for the theories, mathematical deductions and algorithms in applying H,~, method are not included in this paper, and the reade...
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