Modified Smith Predictor Based Parallel Cascade Control Strategy for Non-Self Regulating Time Delay Processes

Abstract

Modified Smith predictor based parallel cascade control strategy is proposed for enhanced control of non-self regulating processes involving time delays. Modified Smith predictor is integrated in the primary loop of the parallel cascade control structure to enhance the closed loop performance. The proposed structures consist of two control loops, a secondary inner loop and a primary outer loop. The secondary loop controller is designed using the internal model control (IMC) method. Then, the primary loop controllers are designed after identifying the overall primary process model. The primary loop has two controllers meant for set point tracking and good disturbance rejection and designed using direct synthesis method. The primary set point tracking controller is designed as a PID with lag filter and the primary disturbance rejection controller is designed as a PID with lead-lag filter. For comparison, a simple parallel cascade control is also applied to non-self regulating time delay processes. Simulation studies have been carried out on various unstable and integrating processes. The proposed method provides enhanced closed loop performances compared to that of simple parallel cascade control.