Research On The Control System Of Compression Refrigeration Unit

Nowadays,with the air conditioning into people's life and work which leads to the energy consumption of air conditioning accounts for about 70% of the total energy consumption of urban buildings in the world.How to choose such an effective way to reduce the energy consumption of air conditioning has become a research hotspot now.Therefore,this paper takes compression refrigeration unit which is commonly used in the field of air conditioning as a research object to study on the energy saving of compression refrigeration unit from optimization and control point of view.Firstly,this paper introduces the composition of the experimental platform of the compression refrigeration unit control system,and analyses its working principle and operating characteristics.Secondly,in order to select the control method which is suitable for the compression refrigeration unit of this paper,the mathematical model of the compression refrigeration unit is established by system identification based on experimental data.The comparison between simulation results and experimental data verifies the validity of this model.Then,this paper presents a set point optimization strategy based on modified superheat constraint for compression refrigeration unit to reduce energy consumption.At first,the steady-state mechanism model and the energy consumption model of compression refrigeration unit are established by the principles of thermodynamics and energy conservation.Then,according to the coupling relationship and physical relationship among the components of compression refrigeration unit,the equality constraints and the inequality constraints of the strategy are given.Basing on the minimum stable superheat curve,the lower limit of the superheat constraint is adjusted online to be the minimum stable superheat value under different heat loads.Finally,minimizing the total energy consumption of the system is taken as the optimization goal and the optimal operation points of the unit are obtained,then the energy saving operation of compression refrigeration unit has been realized.Results of the experiment show that the modified method has a better energy saving effect than the existing methods under variable load conditions,the highest energy saving is about 2.17% and the lowest is about 0.23%,which verifies the effectiveness of the proposed method.Finally,since compression refrigeration unit has problems of delay,coupling and external disturbance,an improved Smith predictive decoupling control based on disturbance observer has been proposed in this paper.First,the disturbance observer is used to observe overall disturbances of the system in the conventional Smith predictive control structure.The time-delay element is linearized by first-order Pade model.Then a diagonal matrix is applied to decouple the compression refrigeration unit.Finally,the tuning of the controller parameter is realized based on the minimization of ITAE criterion.The robustness of the whole control system is discussed.Through the simulation,the proposed method can provide a better decoupling for the compression refrigeration unit,better robustness and immunity.Moreover,it saves about 0.71% energy.