Nonlinear PID-based temperature control techniques in greenhouses using natural ventilation

Abstract

Greenhouses provide controlled environments for cultivating crops. This work explores the design of PID-based greenhouse climate control techniques using natural ventilation, considering both measurable disturbances and operational constraints. A nonlinear model was developed to relate natural ventilation (the primary climate actuator) with interior temperature in greenhouses, the critical factor being the relationship between air flow rate and vent aperture, which is a source of uncertainty in the related literature. Novel calibration issues are included for this term. The nonlinear model is used to devise control strategies combining PI control and feedback linearization. The resulting simulations and robustness analysis, which accounts for uncertainties in the relevant parameters, demonstrate that the combination of PID and feedback linearization techniques is a suitable control approach. In summary, practical tradeoffs can be achieved between setpoint tracking, disturbance rejection, control effort, and robustness.