Background and Objectives: In this paper, a novel objective function is proposed for designing the power system stabilizers (PSSs). Although the object of the previous designs was to enhance the critical modes' stability, the derived stability indices were, to some extent, low and in some cases not acceptable at all. The prospect of attaining higher stability motivated authors to design a new objective function in this study. In all the previous objective functions, the same priority is accorded to all modes, and an objective function is generally defined. A novel function is presented, called Variable Slope Damping Scale (VSDS), based on the assumed variable slope for the straight line in the fan-shaped region, which is an area in the complex plane for determining the eigenvalue placement range, with a reference tip at the negative point. This can be an efficient solution to the low value of critical modes' stability. In general, more damping for critical modes and lower priority for searching non-critical modes are taken as key points. The result of applying VSDS leads to a high value of damping scales for critical modes. The nonlinear simulation results and eigenvalues analysis has demonstrated that the proposed approach in this study is highly effective in damping the most critical modes.
Methods: The proposed method assumes a variable slope for the straight line of the convergence region (specified area for placement of poles) in a fan-shaped type. Indeed, the increase in critical mode's damping scale is taken into account as a key point to introduce a powerful objective function.
Results: The value of the damping scale and also the overall dynamic stability of the test system has increased by using the proposed objective function.
Conclusion: Also, it has been shown that a variable slope convergence region is better than that of a constant slope one to the optimal tuning of WAPSS. In other words, the value of the damping scale with the proposed method over the existing techniques clearly shows that the proposed objective function is more effective than the other ones.
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