A robust adaptive controller for bio-reactors with saturated input and uncertain varying plant parameters

In this paper an adaptive controller for bioreactors is developed, using a mass balance model based on an unique biological reaction pathway. The control scheme is constructed from Lyapunov-like function method and an extended Luenberger observer which allows handling the control input saturation. The measured methane flow rate is used to handle the uncertainty on the reaction rate and an update law to handle the uncertainty on the proportional coefficient of the reaction rate. Under the assumptions of the system model are considered: i) the control input is saturated, ii) the values of the kinetic parameters, the biomass concentration and upper or lower bounds are unknown and iii) the output methane flow rate is measured. The main controller characteristics are the following: i) the closed loop states are bounded, ii) the observer error converges to a residual set whose size is user-defined, iii) the tracking error converges to a residual set which is user-defined; provided, the control input does not reach the extreme values. The controller performance is evaluated via numerical simulations showing excellent results.