Modified parallel cascade control structure for integrating processes

In process industries, parallel cascade control structures are widely used to improve the dynamic performance in the presence of disturbances. Majority of the parallel cascade tuning strategies reported in the literature focuses on stable process models. Hence, this article presents an improved tuning strategy for time delayed integrating process models. The proposed parallel cascade control structure has three controllers: a stabilizing (P) controller, a primary (PI) controller and secondary (PID) controller. Settings of primary and secondary controllers are obtained by equating the derivatives of desired and actual closed loop transfer functions whereas stabilizing controller is designed as per Routh-Hurwitz stability criterion. Examples are included to illustrate the performance and robustness of the proposed tuning strategy.