Study On Model-based Control Algorithms For Greenhouse Environment

Firstly given in the first chapter of this paper are a general description about development on greenhouse environmental control technology at home and abroad and some problems existing in this field in China. Secondly the research on greenhouse climate models and control methods at home and abroad are discussed in this paper and the temperature and humidity models of greenhouse we adopt in this paper are given and analyzed. Then based on rational analysis of the history environmental data in the greenhouse, temperature model can be approximated as a first-order model with dead time. Later based on this approximate model, we employ the parameter self-tuning formulae in literature [35] to obtain optimum PID controller settings for minimization of time weighted integral performance criteria. The PID controller thus obtained is used to control the greenhouse temperature. Compared with other parameter self-tuning methods of PID controller, the closed loop system with the PID controller with optimum parameters shows better performance including smaller overshoot and shorter settling time. Then we design a decoupling controller to solve the coupling between the temperature and humidity. Moreover, considering the temperature and the humidity subsystems as independent subsystems after decoupling, we design parameter self-tuning fuzzy controllers to control them respectively. Finally we make a summary of our work and point out the topics of further research.