Improved Tuning of Cascade Controllers for Stable and Integrating Processes with Time Delay

In process industries, cascade control is one of the commonly used techniques to improve the performance of a single loop control structure when there are disturbances associated with the manipulated variable. In the present work, tuning rules have been proposed for series cascade control structure considering stable and integrating process models with time delay. The primary controller is a Proportional-Integral-Derivative (PID) controller in series with a lead/lag filter whereas the secondary controller is a Proportional-Integral (PI) controller. The direct synthesis approach is used to design both the controllers. The main advantage of the proposed tuning strategy is that it yields improved regulatory performance than some recently reported tuning strategies. Simulation examples are given to illustrate the superiority of the proposed scheme as compared to the recently reported tuning strategies.