Hybrid Modeling Method Based On Mechanism And Data For Single-effect Absorption Refrigeration System

In the current era of increasingly scarce energy,absorption refrigeration systems have once again become a focus of research and attention.The traditional absorption refrigeration system is designed under the standard conditions.When the environment temperature,indoor heat load and other working conditions change,the system refrigeration efficiency(COP)is often difficult to achieve the real-time optimal value.Therefore,it is of great significance to optimize the system in real time and improve the efficiency of the system when the working conditions change.However,the absorption refrigeration system is a complex system with multivariable,strong coupling,and multi-interference.It is very difficult to establish an absorption refrigeration system model suitable for system optimization control,which limits the wide application of various real-time optimization control strategies.Therefore,the modeling method of the absorption refrigeration system is studied in this paper.The hybrid modelling method is used to propose the modeling of the generator and absorber of the main components of the system.The research work of this article mainly includes the following contents:Firstly,the research background of the project and the research status at home and abroad were reviewed and the necessity of the research was pointed out.The hybrid static model of generator and absorber was established by using hybrid modeling method based on mechanism and data.Starting from the basic laws of thermodynamics(Conservation of energy and conservation of mass),the model derives the physical model of the generator and absorber,and the variable which has a large influence on the system and easy to measure is used as the input and output variable of the system;the variables that have little influence on the system and the thermodynamic constants such as the number of heat transfer systems and the constant pressure and the specific heat are total.The parameters are identified by using nonlinear leastsquares and experimental data.In the process of parameter identification,changes in the operating conditions of the system are simulated by changing the heating amount of the heater.Therefore,the selected experimental data is more representative and the identified model has a wider application range.The experimental simulation results show that the established generator and absorber model can accurately predict system performance under various operating conditions.Then,the model of the generator,absorber,evaporator,condenser and other components of the absorption refrigeration system is built in Matlab,and the overall model of the system is built based on the input and output relationships among the components.The system model is simulated by changing the heating quantity of the system and the opening value of the electronic expansion valve.Simulation results show that the trend of the response curve of the main variables of the system is similar to the experimental results.Finally,the optimization problem of the absorption refrigeration system is described.The static model of the generator and absorber is taken as the equality constraint of the optimization problem.The optimization method is used to optimize the operation variables of the system by the optimization method proposed by the previous project group.Utilizing the optimal result of the refrigerant superheat at the outlet of the evaporator as a set value,a PI control strategy for controlling the evaporator superheat using an electronic expansion valve is proposed.This strategy utilizes a new robust identification method to identify the system parameters of the first-order plus lag,and uses the improved Ziegler-Nichols parameter identification method to obtain the parameters of the PID controller,and simulates the designed controller in Matlab.The simulation results show that the control effect is good.The generator and absorber model proposed in this paper is simple,effective and less computation.It will be widely applied in the optimal control of absorption refrigeration system.