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Vol: 50(64) No: 1 / March 2005       Improving Disturbance Rejection by Means of a Double Parameterization of the Symmetrical Optimum Method Zsuzsa Preitl Budapest University of Technology and Economics, Budapest, Hungary, phone: +40-256-403229, e-mail: zsuzsa.preitl@aut.upt.ro Keywords: PI(PID) controller design, symmetrical optimum, load disturbance rejection, increase of robustness. Abstract The paper presents a new efficient tuning method for PI, PID controllers, based on the Symmetrical Optimum (SO) Criterion [1]. The method, dedicated to benchmark type plants with one time constant much larger than the others, is based on a double parameterization of the SO Criterion: - one that extends the optimization relations; - a second one that characterizes the ratio between the largest and smallest time constant. Compared with the tuning methods based on pole-zero cancellation, this method ensures better performances as far as load disturbance rejection is concerned. 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