Design And Implementation Of Electrically Heated Boiler’s Temperature Control System

Electrically heated boilers, as the clean, safe and high efficient industrial equipments, are widely used in industrial areas and people’s daily life. However, due to the characteristic of big lag time, the overshoot is easily emerged in the process of temperature rising. At the same time, the large overshoot is not expected in temperature control system. Thus, improving the control performance and making sure the reliability of this temperature control system are not only the guarantee for product’s quality but also the premise of manufacturing safely.The inner tank’s water temperature is served as the control plant. Firstly, the physical characteristics of this control object are analyzed on the basis of energy conservation law. And then, the "ascending curve method", which is based on experiments, is used to calculate the control plant’s transfer function.Programmable Logic Controller (PLC), with its high reliability, powerful functionality and convenient usability, has been widely used as the mainstream solution in industrial automatic control field. Along with the development of computer technology, the capabilities of PLC are significantly improved too, especially on the abilities of data processing and logical operation. Because of their outstanding properties, various complex control algorithms which aimed at different controlling levels and needs can be implemented on PLC system.In this paper, the Matlab/simulink toolbox is served as the platform for simulating controlling methods aimed at time delay system. And then, the dynamic characteristics of different controlling schemes are compared according to the simulated response curve. Guided by the simulation results, the Siemens S7-300PLC is chosen as the controller in realizing the three available control algorithms:the conventional PID control, the middle differential feedback control and Dahlin’s algorithm control. Those three controlling functions are all implemented by the method of structural programming. The upper computer use Wincc V7.0as process monitoring development platform, to make the real-time monitoring configuration interface and the parameters’setting interface. In this paper, three different control schemes are used to accomplish the electrically heated boiler’s temperature control System, by using PLC. Through the analysis of real effect, middle differential feedback control and Dahlin’s algorithm control are all able to obtain the ideal control performance.