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Power system angle stability can be improved by a wide variety of controls. Some methods have been used effectively for many years, both at generating plants and in transmission network. In this paper, two methods are proposed to improve control stability. The first consists to find the critical clearing time (CCT) by equal area stability criterion and numerical integration. The second interests to fuzzy logic controllers. For this last method, we present the nonlinear model with a Takagi-Sugeno fuzzy model. Then a model-based in fuzzy controller design utilizing the concept of the so-called "parallel distributed compensation" (PDC) is employed. Stability analysis and control design problems can be reduced to linear matrix inequality (LMI) problems. Therefore, they can be solved efficiently in practice by convex programming techniques for LMI's. A single machine infinite bus system is analysed with the proposed methods.