A methodology is proposed to identify both process and disturbance dynamics in order to improve the performance of control loops under PID control. The information recorded by a common DCS after a persistent perturbation has affected the plant from desired operating conditions is sufficient for the application of the procedure and no additional tests are required. The identification is based on a simplex algorithm and performs a numerical approximation; results are compared with a linear least square identification algorithm which allows an analytical solution under the assumption of equal process and disturbance dynamics. Results for a wide class of process dynamics show that the simplex approach allows a more efficient identification and permits a model based design of the controller, resulting in highly superior closed loop performance. Robustness specifications can be included in the design. The relevance of the problem and the reliability of the proposed identification and design procedure are confirmed by applications on industrial data sets. The algorithm is implemented in a performance monitoring system operating in refinery plants.
©2011 Walter de Gruyter GmbH & Co. KG, Berlin/Boston