Hierarchical predictive control strategy of microalgae culture in a photobioreactor

In this paper, the problem of trajectory tracking of a nonlinear system with unknown but bounded model parameters uncertainties is addressed. The proposed control strategy combines a robust model predictive control law with a proportional-integral (PI) regulator. The predictive controller guarantees the tracking of the reference trajectory, whereas the PI regulator ensures a good tracking accuracy. The proposed robust predictive controller considers only the most influential model parameters (chosen from a sensitivity analysis), and involves the minimization of a regularized optimization problem. This new formulation of the predictive controller ensures a good trade-off between tracking accuracy and computation time. The developed hierarchical strategy is applied to a macroscopic continuous photobioreactor system, for regulating the biomass concentration at a chosen setpoint. Finally, the proposed strategy is validated in simulation to assess its efficiency.