Study On Industrial Boiler Water Level Control System

The boiler is a necessary power equipment of industry sectors such as generation of electrical energy, chemical industry, oil refinery, papermaking and refinement of sugar and so on. The auto-control is very important to ensuer the boiler's security and stability. At present, in some small-and-medium-sized enterprises of our country, most of the boilers are also controlled by instrumentations and relays, which can't be satisfied with the production request. Therefore, through by using advanced control technology, the boiler control system not only can guarantee the safety in production, but also can save the energy and improve efficiency, which has good market development and investment prospect.The boiler which acts as a controlled object has the characteristics of nonlinear, unstable parameters and exact math model unknown, the problem of whose modeling and control becomes the focus of attention. The boiler water level is an important index of the industry boiler's safety and stability. It is of great importance to control water level in definite range, which can increase the quality of steam, reduce the waste of equipment and ensure the safety of the whole system operation. Currently, most of methods on the boiler water level control adopt the routine PID control. On the foundation of acquiring math model of controlled object, we adjust the three parameters of PID controller in order to achieve good control effect. As to the industry boiler water level system has more complicated dynamic characteristics, we can't obtain accurate math model. Meanwhile,the routine PID control parameter is invariable. It is difficute to adapt to a variety of disturbance and controlled object changes. People is not satisfied with the methods on control effect.The fuzzy control based on manpower experience summarizes and describes the skills of woker's practical experience, which is expressed by using phrases, and could gain qualitative and nonprecise control rules without mathematics model of controlled object. Fuzzy controller has outstanding advantages which does not rely on mathematics model of object and has a strong ability to adapt. This paper presents the study on the methods combined with fuzzy-control and PID control theories, which makes a simulation on the boiler water level model. This article has carried out detailed analysis to the boiler water level's dynamic characteristics and several common control algorithms. According to the actuality control of boiler water level, this paper brings up PID control rules based upon fuzzy reasoning,designs the fuzzy adaptability PID control system which has 2-inputs of the error and rate of error change and 3-outputs of Kp,Ki,Kd of PID controller. This system gets over the disadvantages of no accurate control effect and difficulty to adjust parameters in the traditional way, which achieves self-adjustment of PID parameters. The designed system was simulated by using MATLAB software. The result shows that the self-adapting ability and robustness of the fuzzy controller are better than that of the traditional PID controller. The controller has high accuracy and fast response, which can effectively control the false water level.