Development And Study On Fuzzy Controller For Refrigeration System

The automatic control of refrigeration equipment has developed from simple single circuit closed-loop control to the multi-parameter combined intelligent control stage,but the research and application of intelligent control is still in its infancy,faced with many problems to solve.Firstly,the mathematical models currently applied in the intelligent control are short of certain commonality and standardization.In the processing of simplifying models,the contradiction between complexity and accuracy is not solved.Secondly,the study of control algorithm used in refrigeration system parameter adaptive fuzzy control to adjust the online is less.Stability and convergence of some control algorithm are also subject to proof from theory and practice research.So the perfection of multi parameter adaptive fuzzy control used in cold storage refrigeration system has important theoretical and practical significance.The object of this study is a small low temperature intelligent control experimental facility,in which compressor and evaporator fan frequency is variable.The adaptive fuzzy controller control cold storage temperature and evaporator superheat.Input parameters of the controller is the compressor frequency and cooling fan frequency and output parameters is t the cold storage temperature and evaporator superheat.In the process of designing controller,based on basic fuzzy control rules and lyapunov stability theory,it’s stability and convergence are proved.Then controller was applied to small low temperature intelligent control experimental facility to research it’s stability and convergence experimentally.The main research results are showed as follow.1.According to thermodynamic knowledge,momentum conservation equation,energy conservation equation and mass conservation equation,mathematical model of refrigeration system applied to controlling was established.The models of refrigeration system components are lumped parameter model and it consists of dynamic equations and nonlinear steady state equations.Based on mathematical model,system state variables,input variables,output variables were determined,and finally the complete mathematical description of cold storage refrigeration system was finished.2.Based on the analysis of cooling system parameters and the coupling of every parameters,the comprehensive control strategy was proposed,which control comprehensively cold storage temperature and evaporator superheat by changing compressor and evaporator fan frequency.And from simple to complex,the refrigeration system of the basic fuzzy controller,variable universe fuzzy controller and a stable adaptive fuzzy controller(supervisory controller,scaling factor adaptive law and parameter adaptive law)were designed.In the process of designing,based on lyapunov stability theory,it’s stability and convergence are proved.3.Controller is applied to low temperature intelligent control experimental facility,experimentally researching it’s performance.Results indicated that in the process of variable control target controlling,control effect is perfect,controller shows good tracking performance,high control accuracy and strong robustness etc.In the process of variable charge controlling,the cold storage temperature control effect is perfect,but the degree of superheat control effect is not desired.After disturbed,the degree of superheat needs a long time to restore stability,and there is obvious overshoot.