Sliding Mode Variable Structure Control And Application In Supercritical Thermal Power Unit

Sliding mode variable structure control has the advantages of fast response speed,insensitive to system parameter change and external disturbance,strong robustness,etc.,so it has been widely applied in practical engineering,especially in electric power production process in recent years.As the main performance parameter of boiler,the regulation and control of main steam temperature is of great significance to the safe,economical and efficient operation of power plant.The main steam temperature of the boiler,as a control object,often shows the characteristics of large inertia,multi-capacity,large delay,and certain time-varying and nonlinear.Traditional cascade PID is difficult to maintain a good control quality.In this paper,a sliding mode variable structure control strategy based on improved super-twisting algorithm is designed for a supercritical once-through boiler in the power plant.The main tasks are as follows:(1)This paper introduces the structure and characteristics of supercritical direct current boiler.In view of the main steam temperature control object has the characteristics of large inertia,large delay,nonlinear and timely denaturation,on the basis of analyzing the static and dynamic characteristics of the main steam temperature control object under the three disturbances of steam flow,flue gas flow and desuperheating water,the basic principle of steam temperature regulation of superheater is expounded,and then the commonly used cascade PID control is introduced.(2)This paper studies the design and related applications of general sliding mode variable structure control,emphatically introduces the definition of sliding mode variable structure control and the design of parameters of sliding mode surface,analyzes the causes and solutions of chattering problems of sliding mode control,introduces the super-twisting algorithm and gives corresponding improvement suggestions.(3)This paper puts forward an algorithm based on modified super-twisting algorithm integral sliding mode variable structure control,the integral element is introduced in the sliding mode control to eliminate the error,the modified super-twisting algorithm is introduced to reduce chattering.And it detailedly introduces the design scheme of the control.The various arguments are given,such as the sliding mode surface ?,auxiliary output function ?,equivalent control law ueq and the switching control law usw.The Lyapunov stability of the system is proved.(4)According to the mathematical transfer function of once-through boiler main steam temperature dynamic models,the main steam temperature sliding mode variable structure control model was built on the Simulink simulation platform to simulate the main steam temperature system and compare its control effect with cascade PID control and general sliding mode variable structure control.The simulation results show that the sliding mode variable structure control method based on the modified super-twisting algorithm has fast adjustment speed,small amount of overshoot and anti-interference ability and the robustness are appropriately improved.