pH Control of Yeast Fed-Batch Fermentation Process by Improved Input-Output Linearization Method

In general, there are many influencing factors in the cultivation of microorganisms, including yeast, among which pH control is of great importance. Since the pH characteristics of yeast fermentation processes are nonlinearity and the production of acid during yeast fermentation is typically nonlinearity, the process pH values cannot be adjusted rapidly and accurately by conventional linear control techniques. Hence, the intrinsic nonlinear characteristics of the pH control system are approximated by several nonlinear models including Hammerstein–Wiener model, and a controller is designed based on the models. To increase the yield in yeast cultures, fed-batch fermentation method should be used more than batch cultivation method. In brief, fed-batch fermentation is a method of continuous addition of the nutrient solution(glucose fluid) following the number of yeast cells present inside the yeast fermentation tank. In this paper, a mathematical model based on chemical equilibrium is proposed to control the pH of an industrial yeast fermentation tank with only inflow, no outflow, and relatively large internal volume, and a controller is designed using the input-output linearization method. The performance of the designed controller is verified by numerical simulation and field experiments.