Modeling and Analysis of PWM Control Strategy for Fogging System

• Main Authors: Sheng-Chien Lee, 李聲謙
• Other Authors: 黃裕益
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/18413640363834120172

博士 === 國立中興大學 === 生物產業機電工程學系所 === 100 === A dynamic environment model was established on the effects of greenhouse cooling on different control strategies in a fogging system. Simulation results showed that by applying a suitable set of control strategy, the indoor temperature dropped and was less than the outdoor temperature of 34.4℃. The temperature reduction degree changed within limits and delayed time. Inversely, when relative humidity and time delay were used as the control factors, inappropriate fogging control strategies would cause the temperature to increase against spraying under high amounts of solar irradiation and lacking of sufficient spraying amounts. The above phenomenon can be avoided when temperature as control factor. Under lower ventilation rate, the indoor temperature would increase against spraying regardless of solar irradiation. In poor ventilation greenhouse ,it is suggested that the natural ventilation rate must been raised then set up fogging equipment in order to achieving expected temperature reduction degree. Experimental data from Chiu’s research have been used to validate the model. The rseults show that the maximum error between simulation and Chiu’s experiment is about 2℃ and the error compared with previous researchs is allowalbe. It means that the dynamic environment model could been used to simulate the effects on different control stategies befor planning future cooling control strategies for a fogging system. Finally, the principle of VETH have been used to develop the process to evaluate the ratio of fogging time to operation period. Actural fogging time and interval time could been evaluated by the ratio with other factor such as fixed operation period, spray’s activation contion based on temperature or spray’s shutoff condition based on relative humidity. It would cause the effect similar to PWM control strategy for fogging system. The rsults can serve as reference for planning future cooling control strategies for a fogging system.