The output regulation design of two bioreactor systems in the presence of self-oscillating behavior and inlet
disturbances is addressed. By virtue of linearization, transformation, tuning parametrization, and some geometric
control techniques, explicit formulations of nonlinear proportional−integral (PI) and proportional−integral−derivative (PID) controllers are obtained. For the prescribed second-order nonlinear system, the model-based
PI controller connected to a linear transformation-based observer is developed. For the general class of third-order nonlinear systems, a PID-type feed-forward/feed-back controller that is connected to parametrized tracking
modes is constructed. Using the numerical approximation for the reconstruction of equilibrium manifold, the
simplified model-based PID control can be easily implemented. Finally, closed-loop simulations show the
satisfactory output regulation performances.