Environmental Parameters Control For Greenhouse

Greenhouse can provide good environment for the cultivation of economic crops. Theremarkable economic benefit and social benefit make greenhouses become an importantpart of modern agriculture. Our country is a big agricultural country, due to the largepopulation and influence of unfavorable environment factors, the cultivated land resourcesare relatively scarce. With the urbanization speeding up, the development of economy ofour country is rapid and harmonious. The development of a high quality, high yield, highefficiency, environment protecting modern agriculture and the improvement of agriculturalscience and technology have became the requirement of social development of our times.The automatic and intelligent control systems of greenhouses are the inevitable trendof modern agriculture development. Considering economic benefit and the differentenvironmental requirements of crops growth in different phases, reasonable controls forgreenhouse temperature and humidity become the key factors of intelligent control.Environment modeling plays an important part in greenhouse control. In order to deal withnonlinearity, strong coupling connection and hysteresis of the model of greenhouse,achieve the temperature and humidity control, in this thesis, based on the mass and energybalance methodologies, a mechanism model of temperature and humidity of greenhouseenvironment is built. To address the nonlinear issue in this greenhouse control system, weget a group of linear system models by linearizing nonlinear system model in differentoperating points. In the light of switching control, based on quadratic performance index,by using different system model parameters at different operating points a trackingswitching optimal controller of temperature and humidity for greenhouse is presented. Byusing Lyapunov method, the stability of switched systems is discussed and verified. Inorder to solve the problems of environmental interference, a discrete sliding mode variablestructure controller is designed based on the equivalent control. The controller has aninvariance character when interference appears.The feasibility and effectiveness of the theories and designs of the two controllers areverified by simulation experiments. The results show that both of the two controllers have favorable controllability and stability. It can be able to track the target value of temperatureand humidity.