Towards discrete time model for greenhouse climate control

This paper presents a discrete-time greenhouse climate model to meet the requirement of model-based greenhouse climate discrete control. In this model, three state variables including the indoor temperature, humidity and CO2 concentration and several control actions are considered. To save several states, algebraic fitting technique and time sequence functions are used to estimate some variables such as the temperatures of cover, canopy and floor. To improve simulation performance of the discrete-time model, polynomial is employed to approximate some unmodeled dynamics, and least square technique and Levenberg-Marquardt (LM) algorithm are used to identify the parameters of relevant terms in the model. The model is validated by a complete greenhouse climate model and a Venlo type commercial greenhouse, and the results indicate that the proposed model demonstrates good simulation performance, and is suitable to be used to greenhouse climate control design.