PD-based ADRC using time-varying gains: An application to microalgal-based bioprocess

Area of Science:

• Biotechnology
• Process Control
• Algal Biotechnology

Background:

• Microalgae cultivation is crucial for various applications but requires precise process control for high productivity.
• Microalgal growth models are complex, involving nonlinear dynamics and external disturbances that challenge traditional control methods.
• Accurate control is essential to overcome uncertainties and optimize microalgal bioprocesses.

Purpose of the Study:

• To develop and implement an advanced control strategy for microalgae cultivation.
• To enhance the robustness and efficiency of microalgal growth models using Active Disturbance Rejection Control (ADRC).
• To identify optimal operating conditions for microalgae using computational tools.

Main Methods:

• Implementation of a proportional-derivative (PD) controller combined with a time-varying gain extended state observer (ESO) within an ADRC framework.
• Utilizing the GEKKO Python package to determine optimal operating parameters for microalgae cultivation.
• Applying the developed control strategy to the growth model of Isochrysis galbana.

Main Results:

• The proposed ADRC strategy effectively eliminated steady-state errors in microalgal growth.
• The control system demonstrated asymptotic convergence to optimal equilibrium, even with unmodeled dynamics and disturbances.
• Numerical simulations confirmed the controller's ability to manage unknown disturbances and achieve stable growth.
• Analysis revealed that the photobioreactor model's stability depends on the dilution rate, potentially yielding one, two, or no stable steady-state solutions.

Conclusions:

• The implemented ADRC with a time-varying gain ESO offers a robust and effective solution for controlling microalgal cultivation.
• This advanced control approach enhances productivity and stability in bioprocesses, addressing inherent model uncertainties and external disturbances.
• The findings contribute to optimizing microalgae cultivation for industrial and research applications, with implications for photobioreactor design and operation.