Tuning Method of PI Controller for Given Damping Coefficient

This paper presents a tuning method of PI controller based on a desired damping coefficient. The plant model described by a first-order lag plus deadtime system is considered. The ultimate sensitivity method presented by Ziegler and Nichols has been still widely used, but it has the disadvantage that gives an oscillatory response. In recent years a less oscillatory response has been judged to be more appropriate for process controls. In tuning PI controller it is often convenient to determine the damping coefficient to obtain the desired control performance. The deadtime element can be approximated by the Pade equation to determine the damping coefficient for the equivalent second-order lag system. For PI control, the integral time is normally chosen equal to the time constant of a plant to degenerate the order of the closed-loop transfer function so that pole-zero is cancelled. As a result, the relations among the gain constant, the time constant, the deadtime of the plant and the proportional gain of the controller are clarified when the desired damping coefficient is provided