IMC-Based Control Strategy for Open-Loop Unstable Cascade Processes

In this paper, a new three degree-of-freedom control structure is proposed for open-loop unstable cascade processes. Enhanced regulatory capacities for both set point tracking and load disturbance rejection are obtained. By virtue of an open-loop control manner for the set point tracking, the nominal set point response is decoupled from the load disturbance response and thus can be quantitatively regulated by tuning the single adjustable parameter of the set point tracking controller. There are two closed loops for rejecting load disturbances, of which the inner loop is primarily responsible for the load disturbances that seep into the intermediate process and the outer loop for the load disturbances injected into the primary unstable process. Both of the closed-loop controllers are analytically derived by proposing the desired closed-loop complementary sensitivity functions, and meanwhile, the robust stability constraints for tuning the two closed loops are analyzed in the presence of the process multiplicative uncertainties. Simulation examples are included to demonstrate the superiority of the proposed method.

[1]  Sunwon Park,et al.  Enhanced Control with a General Cascade Control Structure , 2002 .

[2]  Sunwon Park,et al.  PID controller tuning to obtain desired closed loop responses for cascade control systems , 1998 .

[3]  B. Wayne Bequette,et al.  Relay Autotuning of Cascade-Controlled Open-Loop Unstable Reactors , 2003 .

[4]  W. Luyben,et al.  Tuning PI controllers for integrator/dead time processes , 1992 .

[5]  Alessandro Brambilla,et al.  An Efficient Structure for Parallel Cascade Control , 1996 .

[6]  Wenjian Cai,et al.  Auto-tuning of cascade control systems. , 2003, ISA transactions.

[7]  C. Hang,et al.  IMC-Based Control System Design for Unstable Processes , 2002 .

[8]  B. Wayne Bequette,et al.  A model predictive formulation for control of open-loop unstable cascade systems , 2002 .

[9]  Wen Tan,et al.  IMC design for unstable processes with time delays , 2003 .

[10]  Hsiao-Ping Huang,et al.  A SIMPLE METHOD FOR TUNING CASCADE CONTROL SYSTEMS , 1998 .

[11]  I Kaya,et al.  Improving performance using cascade control and a Smith predictor. , 2001, ISA transactions.

[12]  Xiaoming Xu,et al.  Quantitative Performance Design of a Modified Smith Predictor for Unstable Processes with Time Delay , 2004 .

[13]  Arthur Jutan,et al.  Nonlinear Inferential Cascade Control of Exothermic Fixed-bed Reactors , 2000 .

[14]  Gu Dan-ying.  Analytical design for a class of open-loop unstable cascade (control) systems , 2004 .

[15]  Ian Postlethwaite,et al.  Multivariable Feedback Control: Analysis and Design , 1996 .

[16]  Tan,et al.  Simultaneous online automatic tuning of cascade control for open loop stable processes , 2000, ISA transactions.

[17]  Evanghelos Zafiriou,et al.  Robust process control , 1987 .

[18]  André Desbiens,et al.  Improved constrained cascade control for parallel processes , 1999 .

[19]  J. Doyle,et al.  Essentials of Robust Control , 1997 .