Feasibility of applying a robust multivariable controller to a nonlinear bacterial growth system

This report documents the results of applying the robust multivariable linear-quadratic-Gaussian/loop-transfer-recovery (LQG/LTR) control design methodology to a nonlinear bacterial growth system. The growth system is modeled in state-space format containing independent white noise processes in the system equations. The objective is to design a control system that would maintain bioreactor operation at a chosen set point in a stable man ner in the face of external disturbances and internal modeling uncertainty. The nonlinear system is first linearized around a nominal operating set point. Then a LQG controller is designed for this linearized system. The control de sign is carried out by using an expert system called CASCADE, developed at the University of Tennessee, Computer simulations, using the original non linear system equations in generating the "raw" measurements, demonstrate that the resultant closed-loop system incorporating the controller is indeed robust. This robust control design approach has wide application potential to industrial scale production of biochemicals using bioreactor systems.