Control and Simulation of FOPDT Food Processes with Constraints using PI Controller

The most common type of controller being used in the industry is PI(D) controller which has been used since 1945 and is still being widely used due to its efficiency and simplicity. In most cases, the PI(D) controller was tuned without taking into consideration of the effect of actuator saturation. In real processes, the most common actuator which is valve will act as constraint and restrict the controller output. Since the controller is not designed to encounter saturation, the process may windup and consequently resulted in large oscillation or may become unstable. Usually, an antiwindup compensator is added to the feedback control loop to reduce the deterioration effect of integral windup. This research aims to specifically control processes with constraints. The proposed method was applied to two different types of food processes, which are blending and spray drying. Simulations were done using MATLAB and the performances of the proposed method were compared with other conventional methods. The proposed technique was able to control the processes and avoid saturation such that no anti windup compensator is needed.

Authors:

• M.Y. Pua
• M.C. Tan
• L.W. Tan
• N. Ab.Aziz
• F.S. Taip

Keywords:

• constraints
• food process control
• first order plusdead time process
• PI

References:

[1] Lavretsky, E., & Hovakiyman, N. (2007). Stable adaption in the
presence of input constraints. System and Control Letters , 56 (6), 722-
729.
[2] Zhang, M., & Jiang, C. (2008). Problem and its solution for actuator
saturation of integratinf process with dead time. ISA transactions , 47,
80-84.
[3] Åström, K. J., & H├ñgglund, T. (1988). Automatic Tuning of PID
Controllers. North Caralina: ISA Research Triangle Park.
[4] Zaccarian, L., & Teel, A. R. (2004). Nonlinear scheduled anti-windup
design for linear systems. IEEE Transactions on Automatic Control ,
49 (11), 2055-2061.
[5] Tavakoli, S., Griffin, I., & Fleming, P. J. (2006). Tuning of
decentralised PI (PID) controllers for TITO processes. Control
Engineering Practice , 14, 1069-1080.
[6] Seborg, D. E., Edgar, T., & Mellichamp, D. (2003). Process Dynamics
and Control (2 ed.). USA: John Wiley and Ins.