| It is hard to establish a precision mathematical model for the greenhouse control system.Firstly the greenhouse system has the characteristics of time-varying, nonlinearity, strongcoupling, large inertia and hysteresis. Secondly the greenhouse system is easily affected bysome uncertain factors such as external climate, types of crops and controlled objectives.Simultaneously, in the process of control, it is hard to achieve the desired control effect to usethe conventional control method as the greenhouse system is a complex system with multipleinputs and outputs. Fuzzy control theory is different from traditional control theory. To bemore specific, fuzzy control does not depend on the accurate mathematical model of thecontrolled system. It is available in an uncertain system or a strongly nonlinear system andhas the characteristics of flexible control, real-time response performance, stability androbustness etc.. Nowadays, although there are various fuzzy control systems applied ingreenhouse, most of them are two dimensional fuzzy control system based on expertiseexperience. And in terms of control efficiency, they could not meet the requirements of actualgreenhouse production.In this thesis, a kind of greenhouse three-dimensional fuzzy control algorithm has beendesigned to obtain the goal of intelligent control of the greenhouse tempreture factor. Andfinally the simulation results of this algorithm have been tested on the verifying platform. Themain research achievements are:(1) Based on analyzing the key factors influncing greenhouse tempreture, theexperiments of inhancing tempreture in winter and decreasing tempreture in summer wasmade. The function of the difference between indoor and outdoor tempreture varied with timegoing on was fitted by the experimental data from opening9kinds of decreasing-tempretureequipments combination and1kind of inhancing-tempeture equipment. Temperatureregulating capacity of the equipment combination in all kinds of indoor and outdoortemperature conditions was also analyzed, which provided the basis for the establishment offuzzy control rules.(2) A kind of greenhouse three-dimensional fuzzy control algorithm was designed withe(the deviation of indoor temperature and its preset value), ec (the rate of the deviation)and w (the temperature difference between indoor and outdoor) as its inputs and the kinds ofequipment control combination as its output. Meanwhile the membership function selectionwas completed and the67fuzzy control rules as well as the corresponding control query tablewith1331commands was established according to the temperature regulating capacity of theequipment.(3) This research built a tempreture model of the microclimate in greenhouse and amodel of fuzzy control system, and then verified the feasibility of the three-dimensional fuzzycontrol algorithm by analyzing real-time tempreture data monitored within24hours andsimulated the control of the equipment through building different tempretures in and out ofthe greenhouse.(4) This research built a verifying platform combining the PC and the nodes of on-sitesupervisory control, and accomplished the design of both the softwares and hardwares of thenodes. And this platform can obtain the indoor and outdoor tempretures regulary and make areal-time control of the equipment by serial ports. As a result, the experimental result of thethree-dimensional fuzzy control algorithm was in accord with the simulation, and also showedthis algorithm has characteristics of high efficiency and good stability. |
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