Metaheuristic Multivariable PI Controller Design for an Ethanol Production Continuous Fermenter

PI controllers are favorable for implementation in most industrial computer controller platforms as well as integrated circuit platforms. In the present paper a multivariable Proportional plus Integral (PI) controller is designed for the regulation of ethanol concentration in a continuous fermenter, being a reactor with several industrial and biomedical applications. Based upon the nonlinear model of the fermentation process, a linear approximant of the process is analytically derived. The range of accuracy of the linear approximant is determined using a mixed norm criterion. Based upon the linear approximant and a metaheuristic algorithm, a multivariable PI controller is designed in order to satisfy stability for the closed loop system, asymptotic command following for the ethanol concentration and model following of the respective closed loop linear approximant system. Performance of the proposed control scheme when applied to the original nonlinear model is satisfactory, even for large external commands.