Robust QFT-Based Feedback Linearization Controller of the Greenhouse Diurnal Temperature Using Natural Ventilation

In this paper, a control scheme based on feedback linearization technique and quantitative feedback theory (QFT) is used to regulate the inner diurnal temperature in a greenhouse located in the south of Spain. In a first step, a non-linear model for the greenhouse is used to design a feedback linearization controller, which provides the vents opening percentage from a virtual control signal provided by a robust proportional integral (PI) controller. The relation between the system output (inside temperature of the greenhouse) and the virtual control signal is given by a first order plus dead time (FOPDT) system. The values for the three parameters of this linear model are identified in the experimental greenhouse by applying several step changes in the virtual control signal and analyzing the process response. Different values for gain, the time constant, and time delay are identified. So, this uncertain linear description for the system is used to design a quantitative feedback theory (QFT) controller with a PI structure. Finally, experimental results are analyzed showing satisfactory performance of the proposed control approach.