The Active Disturbances Rejection Control Of Two Typical Thermal Objects

Thermal system has several complex features such as strong coupling, time-varying, large delay and severe non-linear characteristics, and it's difficult to establish a reliable mathematical model of dynamic process, so that the traditional control methods hardly achieve the desired control requirements. Active disturbance rejection control (ADRC) has simple structure, and can estimate and compensate the system disturbances. ADRC also can effectively inhibit the effects of disturbances of control system, overcome the dependence on mathematical models, and has a good robustness. In this paper, ADRC scheme was presented for two typical thermal objects—the steam generator (SG) water level of nuclear power plant and the ball mill pulverizing system of thermal power plant.SG water level object not only has obvious nonlinear, time variability and uncertainty, but also has the obvious "false water level" phenomenon. In order to resolve the main problems that exist in the SG water level control system,ADRC scheme was presented in this paper.The generalized state equation of SG water level object was established by analyzing the process of SG water level fluctuation, and a SG water level controller was designed based on active disturbances rejection control theory. In the system extended state observer was used to estimate and compensate the"internal disturbance"and"external disturbance", at the same time, the stability and rapidity of the control system were improved through the nonlinear control system. Besides, the comparative simulation tests of the controller under the step response of SG water level and different disturbances was carried out, and the results show that the SG water level control system which was based on ADRC has a better quality and can effectively inhibit the "false water level" phenomenon that caused by the steam flow disturbance .Ball mill pulverizing object is an important equipment of thermal power plant and also one of the major energy-consuming equipments. Ball mill pulverizing system has many characteristics, such as multi-variable, strong coupling, time variability, and the difficulty of establishing an effective mathematical model of dynamic process. The conventional control method is difficult to be effectively applied in the pulverizing system. In this paper, based on analyzing the object structure of Ball Mill Pulverizing System, the ball mill pulverizing system was regarded to be composed of two single-loop subsystems–temperature loop and negative pressure loop, and the dynamic coupling between the subsystems was regarded as an external disturbance; each single-loop treated as a separate control object and the corresponding ADRC controller control system was designed, then these two ADRC controllers establish the whole Ball mill pulverizing control system. In the system the ability of ADRC was used to estimate and compensate the dynamic coupling between the loops, and to realize the decoupling control of ball mill pulverizing system. This paper examined the control performance of the control system through simulation experiments, and compared with the conventional PID decoupling control system, the results demonstrated the effectiveness of the ball mill pulverizing control system based on ADRC.The disturbance rejection control technology, which used in the complex thermal process control system, is able to effectively inhibit the effects of disturbance of control system, and obviously reduce this system's dependence on mathematical models. ADRC provides a new way for designning thermal process control system.