Stabilization of integral plus dead-time processes by digital PI controller

This paper investigates the problem of stabilizing integral plus dead-time (IPDT) processes using a digital PI controller. For handling the problem without loss of generality it is assumed that the ratio of process time-delay to the system sampling period is an integer number, say n. It is observed that the degree of closed-loop system characteristic polynomial is n +2. Since n is typically a large number the usual stability test techniques, which are used in delay-free digital control systems, are not utilizable to solve the underlying problem. Therefore a graphical method that is similar to the D-partition technique is presented to solve the problem. Numerical example is given to illustrate the ability of the proposed method.