In this paper at first MS method is described then as a new application it is used to determine the optimum sites to allocate PSS. This method can investigate the nonlinear behaviour of the studied system and provides the improved performance regarding the PSS controller which is not obtainable through linear approaches. In the proposed method the second-order participation factor is calculated based on MS approach and utilized for selecting the best machine for placing a PSS .Two- area four-generator power system [4] shown in Fig1. is used to show the validity of the proposed method. This study is performed under different degree of system stress. It is shown that the proposed technique results in improved PSS location that is not accounted for by conventional methods. It is shown that under high stress condition, the conventional method suggests different machines for PSS compared with proposed method; this is due to the absence of nonlinear information in the analysis.

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