Simple Tuning Rules for Integrating Processes with Large Time Delay

In the present article, controllers of the modified Smith predictor are designed for pure integrating, integrating plus first order and double integrating processes with large time delays. The direct synthesis approach is used to tune the set point tracking controller. Suitable values of the desired closed loop time constant that satisfies both robust stability and robust performance conditions are provided based on extensive simulation studies. The PD controller, which is used for load disturbance rejection, is designed so as to achieve a specified slope () of the Nyquist curve at the gain crossover frequency. The gain crossover frequency that corresponds to a phase margin of 45 degrees is suggested for all three considered integrating processes. Furthermore, is recommended as 45 degrees for double integrating processes and 90 degrees for pure integrating and integrating plus first order process models. Two simulation examples are considered to illustrate the usefulness of the proposed tuning rules.