Simple Tuning Rules for Feedforward Compensators Applied to Greenhouse Daytime Temperature Control Using Natural Ventilation

Abstract

In this work, simple tuning rules for feedforward compensators were applied to design a control strategy to regulate the inside air temperature of a greenhouse during daytime by means of a natural ventilation system. The developed control strategy is based on a PI (Proportional-Integral) controller combined with feedforward compensators to improve the performance against measurable external disturbances such as outside air temperature, solar radiation, and wind velocity. Since the greenhouse process dynamics is very complex and physical non-linear models are mathematically complicated, a system identification methodology was proposed to obtain simpler models (high-order polynomial and low-order transfer functions). Thus, an easier procedure was completed to tune the PI controller parameters and to obtain the feedforward compensators expressions by following a series of modern and simple tuning rules. Simulations with real data were executed to compare the control performance of a PI controller with or without the addition of feedforward compensators. Moreover, real tests for the developed control strategy were carried out in an experimental greenhouse. Results demonstrate an enhanced control performance with the presence of the feedforward compensators under different weather conditions.

Control climático de invernaderos con compensación de perturbaciones medibles

“…La temperatura del aire en el interior del invernadero afecta considerablemente a los procesos fisiológicos de las plantas y, por tanto, es importante regularla en un rango adecuado en función de la variedad de cultivo y la ubicación del invernadero. Esto acelera su crecimiento y aumenta la calidad de la producción a la vez que economiza el consumo de energía [6,9,10].…”

“…La ventilación natural facilita el intercambio de aire entre el interior y el exterior del invernadero. El aire exterior, generalmente más frío que el interior, tiende a rellenar las capas más bajas del volumen del aire, y el aire caliente asciende a las capas más altas, saliendo al exterior a través de las ventilaciones cenitales [6,9].…”

“…En cuanto a técnicas de control, existen numerosas publicaciones en la literatura [9,10]. En relación con las tratadas en este trabajo, cabe destacar control PID [2,3,11], control anticipativo [4,6,8] y modificaciones al control basado en linealización por realimentación [1,5,7]. Es en esta última técnica de control en la que se basan las principales aportaciones de este trabajo, desarrollando un algoritmo básico que permite controlar la temperatura del invernadero en todo el rango de operación.…”

Research on thermodynamic simulation modeling and air temperature control of solar greenhouse

“…Thus, the whole greenhouse is a complex MIMO, multi-disturbance nonlinear dynamic hysteresis system [7], [8] with a major control method -ventilation. In order to fit the actual conditions of the greenhouse, many scholars have studied the simulation types and model compositions of the greenhouse as well as the model building methods, like Montoya-Ríos used Autoregressive Exogenous (ARX) model for the simulation of the environment inside the solar greenhouse [9], inputting actual seasonal temperature data sets for simulation, which the advantage is easy to model and fast to compute, but the disadvantage is that this model is generated by fitting the past data, unable to reflect the influence of various physical quantities in the greenhouse; Mobtaker simulated and studied the heat transfer in greenhouses with different orientations and structures [10], whose studying objects included the greenhouse with slope-type structure and east-west orientation used in this paper, while Huang L simulated and studied the solar radiation transmitted into the solar greenhouse [11]. Also, the physical formulae of the above-mentioned articles were referred to when the model in this paper was established.…”

Estrategia de control selectivo de temperatura y humedad para un invernadero solar chino con un enfoque basado en eventos

“…En algunas instalaciones demostrativas de CSG, sí se suelen incorporar controladores convencionales para la regulación de consignas. No obstante, el control PID para regular la temperatura en el interior de los invernaderos ha sido ampliamente estudiado para invernaderos ubicados en otros lugares, como en Almería (Beschi et al, 2014;García-Mañas et al, 2021;Montoya-Ríos et al, 2020). Además, se han propuesto otros métodos de control, como el control basado en eventos, para disminuir el esfuerzo energético requerido para regular variables de interés (Pawlowski et al, 2016).…”