Control of unstable bioreactor with dominant unstable zero

Design of a controller by synthesis method for an unstable bioreactor with a dominant unstable zero gives a PI controller. For such dominant unstable zero, it is shown that the integral time is negative. The stability analysis of such controlled system, is given. When the measurement delay is considered, the method requires a PI controller with negative integral time and a first order unstable filter. Theoretical analysis on the condition at which the system can be stabilized, is also given. Simulation results are given for the robust performance of the controller for perturbation in the controller settings. A set point weighting is proposed for the controller to reduce the initial jump in the response and also the undershoot.