DYNAMIC BEHAVIOR OF A CONTINUOUS STIRRED BIOREACTOR UNDER CONTROL INPUT SATURATION

A continuous stirred bioreactor with open-loop periodic behavior is an alyzed under closed-loop conditions, using the dilution rate as contro l input. In the absence of control input bounds, the limiting substrat e concentration converges to set point. When stringent bounds on contr ol input are imposed, it becomes permanently saturated; then a limit c ycle is generated, and the substrate concentration oscillates around a n equilibrium point induced by saturation (EPIS). Suitable conditions are developed to avoid the presence of this closed-loop limit cycle. W hen the above conditions are satisfied, numerical simulations show tha t the substrate concentration in the closed-loop bioreactor has no per manent oscillations, the EPIS disappears and the limiting substrate co ncentration converges again to set point, in spite of the control inpu t bounds. (C) 1998 SCI.