Control Strategy Of Chilled Water Pumps In Central Air Conditioning Based On Hybrid System

Energy consumption of central air conditioning has a large part of building energy consumption,accounting for about 50-60% of the total.Under the social background of advocating green technology and sustainable development,central air conditioning becomes the key object in building energy conservation and emission reduction.Effective energy saving control for central air conditioning is an important issue in the field of industrial engineering and a hot spot of theoretical research.According to the research,the chilled water system of the central air conditioning is a typical kind of hybrid system.Its energy-saving control is mainly realized by changing the flow of the water system through the flow conversion and switching action of the pump group,which embodies the continuous and discrete dynamic characteristics with the goal of minimum energy consumption.According to the change of cooling demand,real-time adjusting the flow rate of the chilled water system can effectively realize the energy saving of the pump group.Therefore,the modeling and energy-saving control strategy of chilled water system based on hybrid system has a strong pertinence.The problems of non-linearity,large time delay and multi-parameters of chilled water system can be effectively solved by hybrid system modeling and control strategy.Therefore,it has extremely important theoretical significance and practical value.In this paper,hybrid system modeling,performance analysis and optimal control method under the objective of minimum energy consumption are used to study the energy saving of central air conditioning chilled water system.In view of the above problems,the following contents are studied:(1)Some modeling types of hybrid systems are studied,a variety of classifications are commonly used: transforming discrete or continuous behavior into another way to transform it into another internal action.The hybrid dynamic characteristics of chilled water pumps are studied,and the system form and dynamic process of switch control and variable flow control are analyzed.The cold capacity transformation and heat balance of room are studied,and characteristics and energy saving situations are analyzed.The method of stability analysis is studied,mainly on three main stability problems,which are divided into the Lyapunov method,the common Lyapunov method,the Lagrange method and other methods.The technical route of the optimal control method and the method is discussed,which is based on different models of hybrid systems.The main research methods of optimal control and robust control for hybrid systems are introduced.(2)The hybrid model and stability of pumps group switch control are studied.Based on the analysis of the switch control system of pumps group,the general model and substructure of the switch control of water pumps group are proposed,and the frame structure of the system is described with examples.The stability of sub structure and the instability phenomenon of multi switch systems are analyzed emphatically.The key factors which are different from the traditional switching system are defined,and the subsystems-group is proposed as the basic unit of switching.In this paper,the structure of the state matrices of subsystems is analyzed,and the inferences of the Hurwitz and Schur stabilities for state matrices are obtained.Combined with the assumption that the matrices are pairwise,the propositions of the system is Lyapunov stability is gained under arbitrary switching condition,and the common Lyapunov function is derived.The conclusion is generalized to a type of parallel structure with appropriate relaxation conditions,and the relevant ideal stability results can be obtained.The stability and instability of multi-switch pumping system are described by comparing and analyzing the three control strategies through simulation.(3)Combained with technologies of variable flow and switching for chilled water pumps without inverter,a type of Double Constraint Mixed Logical Dynamical Systems model is proposed.The model is described in the form of mixed logic inequalities,including state variables,control variables,logic variables,auxiliary variables,double constraint switching rules,critical values,minimum errors and many other indicators.By discussing the problem of non-zero switching point,the equivalent relation of logical expressions under the implication relation is deduced.By explicitly switching the upper and lower threshold values,the system state dependent switching rules are determined.The double constraint logical dynamic model is applied to the energy saving control of the chilled water system in the central air conditioning system.The transfer process of the cooling capacity from the chilled water system to the air system is analyzed,and the behaviors of switching and variable flow of the pumps realise energy saving.Finally,through simulation analysis of switching action,flow conversion process,room temperature change and power saving,the applicability of the model and control is analyzed.(4)Combained with technologies of variable frequency and switching for chilled water pumps with inverter,a method of chilled water system based on hybrid dynamic control strategy is proposed.A model of pump speed optimization based on vector control is established.The model has better electromagnetic characteristics and torque response effect.Taking into account the load characteristics of the water system,the vector control method is used to adjust the water volume of the pump in real time,so that it has the function of variable flow control.The switching control strategy,the cooling allocation and the average temperature difference method are used to achieve the control purpose.The mixed dynamic characteristics of the chilled water system in the central air conditioning are described by the variable flow regulation and the switching(ON/OFF)actions of the pump.It reflects better dynamic characteristics and control effect.Finally,an example is given to illustrate the control process and energy saving situation through MATLAB simulation analysis.