Fuzzy logic has been gaining increasing acceptance in control applications during the past few years. Usually, the membership functions and control rules of fuzzy logic controller are determined by trial and error which is cumbersome and time consuming. Therefore, to surmount such a drawback, this paper makes use of the Genetic Algorithm (GA) technique for optimal tuning of the parameters of the Fuzzy Logic Controller (FLC) used for the switching of the thyristor controlled braking resistor to improve power system transient stability. The braking resistor is installed at each generator bus, where rotor speed of the generator is measured to determine the firing-angle of the thyristor switch. By controlling the firing-angle of the thyristor, braking resistor controls the accelerating power in generators and thus improves the transient stability. The effectiveness of the proposed method has been demonstrated by considering both balanced (3LG: Three-phase-to-ground) and unbalanced (1LG: Single-line-to ground, 2LG: Double-line-to ground and 2LS: Line-to-line) faults at different points in a multi-machine power system.
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