Co-operative control of multi-input single-output processes: On-line strategy for releasing input saturation

A practical problem frequently encountered in industry but not usually addressed by researchers is output unreachability under input saturation: For a large disturbance or set-point change, the process variable may never reach the set-point even when the manipulated variable has been driven to saturation. The process variable can be brought back to the set-point only by activating auxiliary manipulated variables. However, the timing of activation remains an open problem. In this paper, a new strategy based on disturbance estimation and output prediction is presented. It can detect unreachability early on ans activate the auxiliary variables in a timely manner so that the process variable will return to the set-point much faster. Simulation and real-time testing on a pilot mini-HVAC system show the effectiveness of the proposed strategy.