Study Of Multivariable Decoupling Control In VAV System Based On LonWorks Technology

VAV system has the feature of multi-variable, intense conpling and nonlinear. When the several control loops in the control system are working together.there is intense coupling among them. The loops influence as well as interfere each other.The coupling may directly affect the property and the stability of VAV system.This thesis focuses on reducing and eliminating the coupling among the control loops by means of setting up the mathematical model of VAV system and designing the decoupling control system. Thus the controlling property and the stability of VAV system may be well improved.Here the theoretical model of VAV system is set up for the first time.Besides,the transfer function matrix of the 5 inputs and the 5 outputs is established by combining the theoretical analysis with the data analysis of experiment. Then the non-linear mathematical model of the five loops is delt with in two method: In the first method, Taylor progression is applied near the working point of the system in order to make the volume of change between the output and the input become similar to a linear relationship. In the second mothed, the non-linear mathematical model realize linear by means of being devided into sections.The study shows that both the motheds are effective in dealing with the non-linear issue in VAV system.In this thesis, the decoupling unit of VAV system is designed in the way of feedforward conpensation. Then the transfer function matrix of the feedforward conpensation decoupling unit of the 5 inputs & 5 outputs VAV system is worked out. The decoupling conpensation unit can change the transfer function matrix of the open loop and closed loop control system into diagonal matrix,so that the coupling among the five control loops is eliminated,and VAV system is decoupled. Before this thesis, similar report is unseen in both domestic and foreign reference.This thesis presents an effective way to design PID controller through a combination of adverse deduce and genetic algorithm. The relationship between PID parameter and the root of the characteristic equation of the closed loop control system has been found out directly. As long as the root of the characteristic equation is within the unit circle of z-plane and the corresponding PID parameter is got, the closed loop control system is sure to be stable. Although the root of the characteristic equation can vary within the unit circle of z-plane,different value may affect the control property differently. Therefore,it is better to optimize the root, here the optimizing method is carried out by genetic algorithm.In this thesis, the VAV decoupling control experiment system based on LonWorks technology is set up by means of combination of Lon Works technology of networks control technology and VAV technology. So far, there is no such report in domestic reference. So the experiment system can be regarded as advanced.This thesis offers a new way to exchange data between LonWorks and Metasys networks. Acturelly, there are two systems in the experiment unit of the VAV decoupling control system. They are LonWorks system and Metasys system. As the communication protocols follow their respective standard, the data exchanging between the two systems becomes difficult. Here an ingenious method is adopted. Since LON net, Metasys net and Visual Basic all support dynamic data exchange (DDE)protocol, the data of LON net can be conveyed to Visual Basic through LNS DDE Server of LON system. Meanwhile, the data of Metasys net can be conveyed to the same Visual Basic through Metalink DDE . Then the Visual Basic is expected to deal with the data, after that, the data are conveyed back to LON net and Metasys net. Thus the data exchange is realized. Simple and practical, this method helps to save the cost of the hardware as well as the time spent in exploiting the gateway.