Performance Comparison of Three Control Strategies for Microalgae Growth Using PIL Simulation

Microalgae are microorganisms that use the energy of sunlight to fix carbon dioxide and to produce oxygen and biomass rich in bioactive compounds. Several models of continuous cultures of these microorganisms are found in the literature. However, this type of non-linear and time-varying bioprocesses generate models do not consider all the dynamics and some of the intrinsic parameters of the cells. This development has prompted researchers to explore different control strategies aimed at monitoring a predetermined operational trajectory (the total biomass, CX*(t)) within a continuous microalgae photobioreactor. This work presents three control strategies: Active Disturbance Rejection Control (ADRC), Intelligent Proportional-Integral (i-PI) and Proportional-Integral (PI) Controller, which are characterized by little dependence on the model. These controllers were implemented and compared using Processor-In-the-Loop (PIL) simulation method. The control signal chosen was the dilution rate, D(t). The setup involved utilizing the STM32F4 Discovery platform from STMicroelectronics for implementation, while a host PC running Matlab/Simulink® software was employed for the design process, code development, and performance testing of the Processor-In-the-Loop (PIL) system. It was observed that the ADRC control strategy exhibited the most effective performance, as indicated by the results derived from error tracking analysis across simulation scenarios, nominal conditions, and external disturbances. Furthermore, an evaluation of each controller's performance was conducted based on various error performance criteria, including Integral Square-Error Criterion (ISE), Integral of Time multiplied Absolute Error Criterion (ITAE), and Integral Absolute Error Criterion (IAE).