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 addr essed by researchers is output unreachability under input saturation: for a large disturbance or set-point change, the process variable may never reac h the set-point even when the manipulated variable has been driven to satur ation. The process variable can be brought back to the sit-point only by ac tivating auxiliary manipulated variables. However. the timing of activation remains an open problem. In this paper, a new strategy based on disturbanc e estimation and output prediction is presented. It can detect unreachabili ty early on and 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. (C) 2001 Elsevier Science Ltd. All rights reserved.