Feedback cooperative control for releasing input saturation

In this paper output unreachability under input saturation phenomenon is studied: under a large disturbance or set-point change, the process output may never reach the set-point even when the manipulated variable has been driven to saturation. The process output can only be brought back to the set-point by activating an auxiliary manipulated variable. A new feedback cooperative control strategy capable of solving such a problem is proposed. In this scheme, the primary manipulated variable is used to handle the transient response while the auxiliary manipulated variable is used to keep the primary manipulated variable away from the saturation. These two manipulated variables are coordinated through a user-defined non-linear function. This function decides when and how the control structure changes. Its parameters determine the interaction between both inputs and the steady state value of each manipulated variable. The effectiveness of the proposed scheme is illustrated in a simulation example.