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Research on Fuzzy PID Control for Cold Storage Refrigeration System

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Tutor: YinJianJun
School: Zhejiang University of Technology
Course: Mechanical and Electronic Engineering
Keywords: Cold storage,Refrigeration systems,Electronic expansion valve,Fuzzy Control,PID,
CLC: TP273.4
Type: Master's thesis
Year:  2009
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The automatic control of the refrigeration system is one of the most effective means to achieve energy-efficient the refrigerator . Cold storage refrigeration system with automatic control of not only energy , but also to guarantee the stability of the storage temperature , low temperature to avoid unnecessary and can make the food quality is stable during storage , slow food surface moisture evaporation . In addition , the use of automatic control can also make cold storage refrigeration system running state parameters of temperature , pressure, etc. remain within the required range , to ensure system safety and efficiency . Small the Freon cold storage refrigeration system for control of the object , the design of the automatic control system of cold storage , the structure of the control system and hardware configuration . The intake pressure as the control target , through slide valve regulating the cooling capacity ; evaporator superheat for the control target , by adjusting the opening degree of the expansion valve , with compressor adjust the flow control strategy . A detailed study of the expansion valve opening degree adjusting system . The target evaporator superheat electronic expansion valve control algorithm , the application of more PID ( or PI) regulator , conventional PID control can not be based on the dynamic process of the system automatically adjusts the control parameters , control accuracy is not high . Fuzzy control robustness without knowing the mathematical model of the controlled object , and has its own advantages in terms of rapidity , but vulnerable to the limited level of fuzzy rules fuzzy control restrictions caused by the steady-state error . This paper analyzes the advantages and disadvantages of the PID control and fuzzy control combined with each other to achieve the complementary advantages . With PID parameters online fuzzy self-tuning to modify PID parameters in real time , ensure that the process of implementation of the electronic expansion valve is always in the optimal state . The design parameters of fuzzy self- tuning PID controller at the same time , program design method proposed by S7-300PLC control algorithm . By MATLAB simulation and experiment show that the the fuzzy PID can adapt to the requirements of the expansion valve opening control system , in response speed , steady state accuracy are superior to conventional PID control has better robustness .
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