A Modified Two-degree-of-freedom IMC Control For Integral Processes Plus Time Delay

Integral processes plus time delay are frequently encountered in industrial process control. These processes usually include the poles at original point and the time delay. Conventional PID control cannot overcome the difficulties of long time delay. Traditional Smith predictor control(PSC) and internal model control(IMC) can not be directly applied to integral processes. In order to overcome the aforementioned shortcomings, scholars proposed many new methods based on the conventional PID control , PSC or IMC during these years. This paper begins with a brief description of the resent research in the field of integral processes plus time delay. Then it explains the basic principle of internal model control, analyses its fundamental properties, explains the controller design method, and analyses the reasons that traditional internal model control can not be directly applied to integral processes in details. After that it introduces a modified two-degree-of-freedom IMC scheme which can be directly applied to integral processes. By adding a controller to pre-stabilize the integral processes, the set-point response and disturbance response are decoupled from each other and can be designed independently. This scheme can ensure internal stability of the closed-loop system and no steady-state errors. The internal stability of the closed-loop system is analyzed. This paper proposed three methods to design the controller to pre-stabilize the integral processes. One method...