Research On Model-Free Control Algorithm And Its Application In Refrigerating Units

In this paper,the model-free adaptive control method was applied to the control of a compression refrigeration systems.In view of the characteristics of the compression refrigeration system such as strong coupling,large time delay,non-linearity and the difficulty of establishing accurate mathematical models,an improved model-free adaptive control method was introduced.Finally,the second-order model of the refrigeration systems was used for simulation comparison tests,and the effectiveness of the newly proposed control method has been verified accordingly.The main research contents and achievements can be summarized as the following three aspects:First of all,in this paper,the single-input single-output model-free control scheme was extended to dual-input and dual-output,and the energy-saving control scheme of compression refrigeration system was given.Aiming at the non-linearity of refrigeration system and the difficulty in establishing accurate mathematical model,the model-free control method was applied to the control of refrigeration system.The control schemes of typical linear and nonlinear systems and refrigeration systems were simulated and compared respectively.The simulation results show that the model-free control algorithm has superior dynamic performance and the output of the refrigeration system is faster and more stable.Secondly,aiming at the large lag characteristic of the actual system,a model-free adaptive control method with delay-rate input rate-of-change constraint was designed,and a typical system simulation with large time-delay was introduced.After that,the improved model-free control method with dual input and dual output was deduced,the model-free control scheme of refrigeration systems was improved,and the scheme was simulated and compared.The simulation results show that the improved model-free control algorithm has good control performance and faster response speed,which can effectively improve the performance of the refrigeration system.Finally,in order to solve the control problem of nonlinear system with time-delay characteristic better,the output error sum was added to the control input criterion function of model-free predictive control algorithm,and then an improved model-free predictive control algorithm was proposed.After that,a typical large time-delay system was introduced to simulate and compare the results.The simulation results show that the improved model-free predictive control allgorithm has stable output and good dynamic performance.