The Application Of Sliding Mode Control In The Thermal Power Units Denitrification Control System

The nonlinear,time-delay and time-varying characteristics of SCR denitrification system in thermal power units,increase the difficulty of actual control.Recently,with the deterioration of the atmospheric environment,the emission standard of nitrogen oxides in thermal power units becomes more stringent,and the requirements of SCR denitrification system control performance are also higher,so it is necessary to find a control algorithm with good performance.Since sliding mode control was introduced,due to the extremely robust,it works well in controlling nonlinear and time-varying system,and attracts widespread attention,and thus has been successfully applied to robotics,aerospace and other fields.Based on finishing transformation project of denitrification system in Datang Luoyang Shuangyuan Thermal Power Plant,the characteristics of denitrification system and the problems existing in denitrification system control at present are analyzed in this paper.Then,based on the combination of theory and application,the performance of the sliding mode control and the buffeting are studied theoretically and the algorithm is improved.The research is applied to the SCR denitrification system.This specific work is as follows:According to the compensating lag characteristics of Smith predictor and the robustness of sliding mode control,the sliding mode controller is combined with the Smith predictor to solve the nonlinear,time-delay and time-varying characteristics of SCR denitrification systems.The chattering of the sliding mode controller is regarded as noise,and the low pass filter is used to filter the control signal,make the control signal smoothing.However,the robustness of the sliding-mode control is related to the switching gain,and the robustness of the sliding-mode controller increases with the increase of the switching gain.The method has a steady-state error when the external disturbance is larger than the switching gain,and the integral sliding mode surface is used to solve this problem.When the initial error is large,the system is overshoot,and the global integral sliding surface is used to make the system state lie on the sliding surface from the initial moment.However,the over-tuning can not be reduced.Type sliding surface to improve the integral sliding mode surface,so that the integral action occurs only in the boundary layer near the sliding surface,thus avoiding the impact of the initial error to ensure the tracking accuracy and obtain good transient performance for the actual system And adaptive control law is used to adjust the switching gain automatically.An adaptive conditional integral sliding mode controller based on Smith predictor is designed and the robustness of the controller is verified by simulation.