Design And Implementation Of Hybrid Control Systems For Experimental Greenhouse Temperature

As a typical representative of facility agriculture, the modern greenhouse combines engineering technology, information technology and biotechnology together to gain agricultural products. During the production process, the inside environmental factors are controlled by switching the environmental control devices, according to outdoor weather conditions and crop growth stages. Among all the environmental factors, the inside temperature plays the most vital role. Appropriate temperature can not only affect crop growth and yield directly, but also accelerate crop growth rate and reduce the occurrence of pests and diseases. Thus it is one of the most important controlled factors in the greenhouse environment control system.Constrained by the production cost and available choice, most of greenhouse temperature control equipment in China is on-off device, or device which lacks feedback unit and thereby cannot be operated as continuous one. Previous greenhouse temperature controllers were mainly developed on the basis of continuous system theory, while ignoring its discrete switching features. As a result, this may cause switching disorder and energy waste. To deal with these problems, this dissertation handled greenhouse plant as a class of hybrid system, and designed novel control systems based on hybrid automata theory.Firstly, fundamental definitions and theorems about hybrid automata were introduced, and application method of the theory was illustrated. Then following the hybrid automata modeling approach, a hybrid control system for greenhouse temperature was designed, and it was showed to be deterministic and non-blocking. In this design, the control system consisted of summer mode and winter mode, and discrete transitions were triggered by real-time temperature data. Experiments in spring, summer and autumn of2014proved its effectiveness.Within the frame of summer mode, natural ventilation, forced ventilation and pad-fan discrete states were used to regulate greenhouse temperature. For each discrete state, a thermal model was developed and calibrated in steady state conditions, moreover its cooling features and energy consumption features were discussed. Then these models were inserted into the hybrid control system as switch conditions to establish a better one, whose discrete transitions were triggered by predicted temperatures, to complete system’s discrete transitions and decrease energy consumption. At last, the strengths and weaknesses of these two hybrid control systems were discussed by comparison experiments.This dissertation has solved greenhouse temperature control problem from the perspective of hybrid system, and verified its feasibility in both theoretical and experimental ways.