Research On Frequency Conversion Control Strategy Of Compression Refrigeration Unit

Recently,with the rapid development of intelligent control theory and computer and frequency conversion technology,many scholars have conducted in-depth research on compression refrigeration systems.Traditional compression refrigeration units usually operate at a fixed rated frequency,and their refrigeration capacity is designed according to standard operating conditions.Although it can meet the needs of the maximum cooling capacity,it does not have the characteristics of dynamically adjusting the cooling capacity as the operating conditions and heat loads change.Therefore,the strategy of real-time frequency conversion control for the compression refrigeration unit as the working conditions and heat load changes can not only save energy but also greatly improve the comfort of the indoor environment.However,the characteristics of compression refrigeration systems are more complex,and it is more difficult to establish accurate refrigeration system models.As a result,many compression refrigeration system control strategies cannot be applied efficiently.For this reason,this paper studies the modeling method of the compression refrigeration system,and adopts the frequency conversion control strategy for the compression refrigeration unit.The following contents are the main research contents of this paper.First of all,this topic shows a robust dual-input and dual-output modeling method for compression refrigeration systems.Using this method to build a system model,one input of the system model is the compressor frequency,and the other input is the electronic expansion valve opening.The method takes the evaporation temperature of the evaporator and the superheat of the refrigerant at the outlet of the evaporator as the output of the system model.Based on the assumption of the first-order plus pure lag relationship between single variables,the least square method is used to identify the unknown parameters of the model from the experimental data,thereby establishing a robust dual-input and dual-output system model.The experimental data of the identification model comes from the experimental platform of the compression refrigeration unit that has been established in the laboratory.By comparing the simulation results of the system model with the experimental results,it can be seen that the system model established in this subject can accurately track the dynamic response of the system and has strong robustness.Secondly,based on the established dual-input and dual-output system model,this topic shows a fuzzy PID control strategy whose parameters can be adjusted online.The control strategy is based on the established system model parameters,and uses the Ziegler-Nihcols parameter tuning method to obtain the initial values of the three PID parameters.This strategy adopts the method of fuzzy theory to learn the real-time running data of the system,and constantly updates the fuzzy rules.According to the change of system working conditions,the PID parameter value can be updated online in real time,which effectively eliminates the problem of poor control effect of the fixed PID parameter controller on the strong nonlinear system.Finally,experiments are used to confirm the performance of the controller.Using set value operation and variable working state operation,the established adaptive fuzzy PID controller is tested.The results show that the controller has good dynamic characteristics when the system working state changes,and the control effect is good.