Research On Fuzzy PID Control For Cold Storage Refrigeration System

The automatic control system of cold storage is one of the best effective methods realizing energy conservation. The cold storage refrigeration system adopted automatic control realizes energy conservation and keeps cold storage temperature steady avoided unnecessary lower temperature and keeps qualification of storing food steady and slows down the water of food surface evaporation. Adopting automatic control system can keep the state parameters such as pressure and temperature the scope of the requisition and ensure the system safety and efficiency.The control object is the small Freon cold storage refrigeration system, designing the automatic control system of cold storage, introducing the structure and hardware configuration of control system. The research control strategy is that pressure of input as control object and adjusting refrigerating capacity by slide valves; the open degree of the electronic expansion valve responding to evaporator superheat and adjusting rate of flow in coordination with compressor.The adjust system of the open degree of electronic expansion valve is researched. The control algorithm of electronic expansion valve responding to evaporator superheat usually adopts PID or PI controller. The Parameters of PID controller couldn't be adjusted in line, has not a high control accuracy. Fuzzy control has a good robustness, not knowing mathematical model of control object and response fast, but fuzzy control can lead to steady-state errors by limited regulation of fuzzy. Analysis on the merits and demerits of PID control and fuzzy control their demerits is combined. The Parameters of PID controller are adjusted adaptively by Fuzzy reasoning. The open degree of electronic expansion valve is being optimal status.Designing the fuzzy-PID controller, a design method of the control algorithm is suggested based on S7-300PLC. The results of simulation and experiment show that the fuzzy self-adjusting PID controller has good dynamic response curvy short response time small over modulation high steady state Precision good dynamic and static performance by comparing with the traditional PID controller.