The Application Of Fuzzy-Pid Controller Combination On The Control Sysytem Of Heat Pump Drying Device Based On PLC

In view of the current problems and insufficiency in China’s vegetables drying process, this subject combines heat pump drying technologies, SCADA and automatic inspection techniques into the vegetables drying process. This paper also includes the development and design of a precise control of heat pump drying system for real-time monitoring and control during vegetable drying process.This study mainly conducted the following researches:(1) It designs a precise control of heat pump drying system. This system is mainly composed of heat pump drying device, data acquisition system and monitoring system. The heat pump drying device consists of compressor, condenser, expansion valve, evaporator, auxiliary electricity heaters, fans composition and other equipments. The data acquisition system includes sensors, PLC and analog input modules. The sensors convert the analog signals such as temperature, humidity, weight and fluid speed to PLC analog input modules. Transmitted by A/D conversion, those digital signals will be converted into engineering values and saved by PLC. Use PPI communications procotol to establishe communication between PLC and PC computer. OPC server gets data through this communication, and displays on the host computer interface in real time. Monitoring system consists of PC monitor function and automation function of lower position machine.Writes user program to accomplish data processing, loop control and fuzzy PID compound control algorithm implementation of the monitoring system with STEP7programming software. In according to the requirements of operator, the combination compressors can control the switching, device control, adjust control fault detect protect and on and off automatiocally. As the management level, the host machine uses configuration software development of monitor and control system implemented as a human-machine interface for real time recording and processing of data, including real-time data display, data archiving, set drying parameters, drying control, alarm information query and display and some other functions.(2) The heat pump drying environment has the features of non-linearity, great inertia and time varying. The conventional system cannot achive an approving effect. Design a fuzzy PID compound controller which does not rely on charged objects mathematical model. Using temperature error and error ratio as input parameters, utilizing fuzzy PID compound algorithms, it can complete the real time tracing for the dynamic characteristic of controlled plant and realize to the precise control in heat pump drying process.(3) The research took carrots as material for multiple sets of drying experiments to verify the performance of the heat pump drying device. In the whole process of drying experiment, heat pump drying device run in normal, temperature and humidity was accurate and stable, the fan’s speed was constant and fluid speed fluctuated slightly, heat supply of heat pump system can change in time. The temperature can reach steady condition when it reaches the setting temperature.(4) The system uses carrots as material for studying carrots’ drying characteristics under different temperature, slice thickness and wind speed.