The Boiler Drum Level Fuzzy Pid Control Study

Boiler is a necessary power plant in the process of industry. In order to ensure the production and security, the auto-control of it is very important. The drum water level is an important variable to be controlled, it is hard to get the mathematic model of the water level with adjustive process, it is characteristic of nonlinearity, instability and time lag. The traditional control mode of three-variable in the drum water level mostly use PID, the effect of it can be improved. The fuzzy control does not need precise mathematic model of the controlled object, it only needs the experience of operator and the data of operating, it has good robustness and is fit to control the system with nonlinearity and lag. But its static characteristic is dissatisfactory, which limit the application of it. It is usual mode in order to eliminate the static error that using fuzzy-PID control.Based on the characteristic of water level control in boiler and fuzzy control, this paper does some exploratory work as follows on applying fuzzy-control to three- variable control mode in the drum water level.1) This paper summarizes the present forms of fuzzy-PID controller. It analyzes and compares the structure as well as performance of water level in boiler combining the characteristic of water level control in boiler, and the simulation with the Simulink on control system is carried out under the action of setting value and noise.2) A control mode is brought forward, which is based on adjusting PID parameters on line via two single-dimentional fuzzy controllers which use error and its integral as input sentence variables. The result of simulation shows the better effect.3) The fuzzy controller of self-adjusting proportion factor is a fuzzy controller that uses a certain way to adjust its proportion factor automatically, and gets the control aim hoped. The paper bring forward a fuzzy controller of self-tuning proportion factor based on PI arithmetic. The result of simulation indicates that the effect of control improves comparing with simple fuzzy controller.4) The part of differential is sensitive to high frequency noise, and easily make the quality of adjust declining. Boiler has the characteristic of lag, the...