MODELING AND CONTROL OF pH NEUTRALIZATION PROCESS FOR A RECIRCULATING HYDROPONIC GROWTH CHAMBER

摘要

In this paper, a pH control system for an experimental recirculating hydroponic growth chamber for the NASA Mars exploration program has been modeled and implemented. The resulting model has a bilinear Weiner type structure. A novel approximation approach is presented to obtain a simplified plant model controller design. Perturbation analysis validates the applicability of the approximation for the specific pH control of a closed-loop hydroponic growth chamber. A modified PI controller that takes into account on-off nature of the solenoid valve actuator was designed to control the pH level. The closed-loop system is shown to be BIBO stable with respect to the original bilinear plant model. Experimental results for reference tracking and disturbance rejection in an operational hydroponic chamber with growing plants have demonstrated the effectiveness of the proposed approach.