| Absorption refrigeration is a green and environmental protection way of refrigeration.With the aggravation of the global energy crisis and the worsening of environmental pollution problems,absorption refrigeration has become a hot spot in the field of air conditioning and refrigeration.However,the weakness of low energy efficiency seriously restricts the promotion and application of the absorption refrigeration systems.In this thesis,the hot water operated single-effect LiBr/H2O absorption refrigeration system is studied from three aspects:system modeling,set point full set optimization and control strategy development so as to improve the energy efficiency of the absorption refrigeration systems through control means.The main contents and research results are as follows:（1）An experimental platform of the absorption refrigeration system is built.The experimental platform of absorption refrigeration system is designed and built according to the basic principle of absorption refrigeration system,using a 5.5k W hot water single-effect LiBr/H2O absorption refrigeration chiller as the core.The platform can realize the functions of data acquisition,display,transmission,storage,variable condition experiment,flexible control and so on.It can be used for the experimental research of model verification and optimal control.（2）The dynamic mathematical model of a hot water operated single-effect LiBr/H2O absorption refrigeration system is established.Through mechanism analysis and by object-oriented modeling method,the lumped parameter sub-models of each components composing the absorption refrigeration system are established.According to the input and output relationship between the components of the system,an initial dynamic model of the system is derived.In order to make the model closed and improve the speed of solution,the physical parameter equations of the LiBr solution and refrigerant water are selected and fitted.After simplification and order reduction,a six-order nonlinear multivariable state space model of the absorption refrigeration system is presented for the first time.The accuracy of the model is verified in two ways by comparing the steady-state simulation results and design parameters with MATLAB calculation under design conditions,and by combining the dynamic comparison of simulation results and measured data under experimental conditions.（3）A full set optimization method for the set point of the absorption refrigeration system is proposed.Through analyzing the coupling characteristics of the absorption refrigeration system,it is found that the operating characteristics of the absorption refrigeration system are the result of the combination of internal and external variables of the chiller,especially the internal state variables are crucial to the energy efficiency of the system.Consequently,the conventional energy consumption analysis method is abandoned,the system steady-state model including all variable sets inside and outside the unit is established,the minimum state variable set is selected,and the highest overall energy efficiency of the system is taken as the optimization goal.Particle swarm optimization algorithm is used to solve the optimal set point of absorption refrigeration system under different loads,and the contribution of internal state variables of the unit to the system energy efficiency is quantified.（4）A dual loop multivariable energy-saving control scheme of absorption refrigeration system is proposed.The absorption refrigeration system usually operates under off-design conditions,and the commonly adopted single loop control scheme cannot realize the efficient operation of the system.Therefore,the open-loop characteristics of the system are studied using the dynamic mathematical model.Based on the results of the full set optimization of system set points,a dual loop multivariable energy-saving control scheme is proposed,which takes the outlet temperature of chilled water and the generator temperature as the controlled variables.In view of the multivariable,pure lag and big inertia characteristics of the absorption refrigeration system,the SISO and MIMO model free control algorithm with delay is pushed by introducing the lag term constraint into the criterion function of model free controller.The model free control algorithm is improved to adapt to the absorption refrigeration system with multi variable,pure lag and large inertia.The simulation results show that the control strategy proposed in this thesis improves the system energy efficiency by19.3%compared with the traditional single closed-loop control scheme.The effectiveness of the control strategy has been verified by the platform experiment. |
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