Automatic Control System Design Of A1000-ton Cold Storage Based On PROFIBUS-DP

As an important part of the cold chain, cold storage is the most common and effective way of food storage by using the performance of refrigeration compressors. In the national production, cold storage is one of the energy-hungry. Automatic control system of cold storage refrigeration is an important way to improve production efficiency and energy-saving rate, to ensure the stability of important parameters of the system, such as temperature, pressure. Commissioned by the enterprise, this project aims to design an automatic control system to improve the automation level of a1000-ton cold storage.With the analysis of the refrigeration process and the equipment composition of the system, combined with the development in the world, the refrigeration automatic control system uses the DP network structure based on PROFIBUS-DP field bus. In the control network, Siemens PLC S7-300is regarded as the level1main station, touch screen MP270as the level2main station, distributed I/O device ET200M and Siemens converter MM440as slave stations. In the control system, the pressure of the low-pressure storing barrel is regarded as the control variable to regulate the refrigeration capacity through the way of frequency control of the refrigeration compressors. The pressure of the high-pressure storing barrel is regarded as the control variable to regulate the supplying water through the segmented control of the pump unit. The temperature of each cold house is regarded as the control variable to achieve the temperature control of each cold house through the refrigerating capacity regulation of each cold house by adjusting the opening of the electric control fluid valve.In this proect, the system uses STEP7V5.4as the programming software of S7-300PLC. Before programming, the first step is to structure the network, then configure the DP network devices (PLC, touch screen, ET200Ms and inverters), assign the network addresses and determine communication formats. In terms of PLC programming, this project foucuses on the communication program design between PLC and the frequency converters MM440, and on the design of the PID control. In terms of HMI design, this project introduces the touch screen project build, the the communication between PLC and the touch screen, the variable connection between the PLC project and the touch screen project.With the analysis of the temperature characteristic of the cold storage, this project simply introduces the application of Fuzzy PID control in the temperature control. This project structures the Fuzzy PID simulation system and the conventional PID simulation system with the fuzzy editor and simulink in matlab7.0. With the comparison of this two simulation systems, it can be perceived that Fuzzy PID control can achieve better control results than conventional PID control.