The PID Fuzzy Gain Setting Control Of Variable Air Volume Air Conditioning System

With the rapid development of Intelligent Building (IB) , Building Automation System (BAS) has come to control and manage the equipment in the building more and more scientifically, economically and rationally. This can not only raise the function and the level of the building, but also save energy. Variable Air Volume (VAV) air conditioning system is superior to other air condition system for its economic and flexible performance and has become the main stays of air conditioning system. But as a complex thermodynamic system, VAV system has many disturbances and is not easy to calculate its parameters.PID control is one of the pioneers of the classical application control strategy. With the strongpoint of straightforward arithmetic, quite robust and good reliability, it has been used in industry control system, which is especially suitable for the control system of the accurate mathematics model can be established. One of the pivotal problems of PID control is the tuning of PID parameters. Conventional method to tune PID parameters is based on mathematics model, according to some or other tuning principle. However the VAV air conditioning control system is a great inertia, pure lag, high nonlinear and time-varying complex system, so the conventional PID control can't obtain a perfect result. On the other hand, conventional PID control has a lot of shortcoming, for example, arithmetic ponderous, invariable positive definite, poor performance, the adaptability to running process, and so on. So employ PID control algorithm only in industry control system always can not reach a good result. In latest years fuzzy control has been developed quickly for its good robust ability. And it does not need an accurate mathematics model of the object, but because of rough rules it brings steady error to result always in this method.With respect to the defects of the two means, this paper leads fuzzy control mechanism into PID control and brings forward a PID fuzzy gain setting control algorithm. In this paper, in the first place, a rough mathematical model of air conditioning room is built up and the fuzzy relation is found among the PID parameters, the deviation and the changing rate of deviation. Secondly, the system unceasingly detects the deviation and the changing rate of deviation in operation. Lastly, according to the dynamic characteristics, the system adjusts the PID parameters through fuzzy adjustment theories to satisfy the control object good dynamic and static performances.Simulating the hypothesis with SIMULINK box in MATLAB environment, thispaper introduces the process of establishing simulating model exhaustively, and analyzed the simulating results. The result indicates that when the parameters change, this control system has good effects and can save energy. So the PID fuzzy gain setting control algorithm is feasible to Variable Air Volume air conditioning systems and has some theoretical and practical value, further more this paper laid a foundation for its later engineering use.