Enhanced Control of Unstable Cascade Processes with Time Delays Using a Modified Smith Predictor

Abstract

This paper presents a simple cascade controller in the enhanced modified Smith predictor structure for control of open loop unstable cascade processes with/without zero. The proposed structure consists of two control loops, a secondary inner loop and a primary outer loop. The method has totally three controllers of which the secondary loop has one controller and the primary loop has two controllers. The secondary loop controller is designed using the internal model control (IMC) technique. The primary loop set point tracking and disturbance rejection controllers are designed using the direct synthesis method. The primary set point tracking controller is designed as a proportional, integral, and derivative (PID) controller with lag filter and the primary disturbance rejection controller is designed as a PID with lead-lag filter. Simulation studies have been carried out on various cascade unstable processes with/without zero. The present method gives significant disturbance rejection both in the inner and outer loops. Also, the proposed method shows significant improvement when compared to the recently reported methods in the literature.

Generalized multi-scale control scheme for cascade processes with time-delays

“…1 P is the nominal model for primary process 1 P . Note that, all the delay components appearing in the characteristic equations (17) and (20) are approximated first using the second-order Padé formula. In this case, we use a higher order approximation of the delay in order to perform more accurate Nyquist stability margin analysis.…”

“…Additionally, several cascade control strategies based on the Smith predictor have also been developed for non-self-regulating processes with time-delays. Among these cascade control strategies based on the Smith predictor are the schemes reported in [15][16][17][18][19][20][21]. It should be noted that, the existing modified Smith predictor schemes for the unstable and integrating cascade processes require the design of several controllers.…”

Synthesis of PID tuning for a new parallel cascade control structure

“…1. Conventional parallel cascade control structure this problem, many researchers (Kaya (2001), Kaya and Atherton (2008), Uma et al (2009), Padhan and Majhi (2012)) use a dead time compensator scheme in the outer loop of the series cascade control system.…”

Design of IMC filter for PID control strategy of open‐loop unstable processes with time delay

“…It is well‐known that control system design for an open‐loop unstable process is more difficult than that for a stable one because of the unstable nature of the dynamics, for which most design tools cannot be used. Many of the important chemical processing units in industrial and chemical practice are open‐loop unstable processes that are difficult to control, especially in the presence of a time delay, such as in the case of continuous stirred tank reactors, polymerization reactors and bioreactors which are inherently open‐loop unstable by design 1–3…”