Co-operative control of multi-input and single-output processes: Problem formulation and solution

In control engineering, a process variable is normally regulated by a process manipulated variable. Due to physical limitations, any manipulated variable will have constraints on its amplitude. A practical problem frequently encountered in industry but less addressed by researchers is the 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, timing of activation remains an open problem, A common practice adopted in industry is to wait for the process variable to reach a new steady state and then take action accordingly. This is time-consuming and may cause serious loss of productivity. In this paper, a new strategy based on disturbance estimation and output prediction is presented- It can detect unreachability early and activate the auxiliary variables timely 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.