Predictive Control For Superheated Steam Temperature Systems With Actuator Saturation Constraint

The control effect of superheated steam temperature has an important influence on the safety,stability and economy of thermal power unit operation.Because the controlled object has a great delay,large inertia,more perturbation and time-varying characteristics,the traditional control method is difficult to achieve satisfactory control effect.In addition,the control system designed to ignore the saturation constraints existing in the water-reducing valve(actuator)usually can not achieve the expected result in practical application,and may even cause system collapse in severe cases.To this end,the paper presents a new cascade DMC-DMC superheated steam temperature control scheme.The program design process is divided into two steps: designing cascade DMC-PID control system and designing cascade DMC-DMC control system:Step one: Aiming at the large delay,large inertia,multi-disturbance and time-varying of the controlled object of superheated steam temperature,the cascade structure of the traditional superheated steam temperature control system is adopted,and the internal circuit can be fully utilized to quickly eliminate the disturbance and improve the system The advantages of operating frequency,while retaining the loop PID controller under the premise of the outer loop DMC controller design.Simulation results show that the cascaded DMC-PID control has better setpoint following capability,anti-jamming capability and robustness than Cascade PID-PID control.However,the cascaded DMC-PID scheme can not deal with actuator saturation constraints.Step two: In order to deal with the saturation constraints of actuators,aiming at the problems of dynamic programming,constrained processing such as quadratic programming and nonlinear programming,which are computationally expensive and not suitable for real-time control,This paper presents a method which turns constraints into linear programming problems.Then,while keeping the loop controller outside the cascade DMC-PID control system unchanged,the linear constraint processing method and the DMC control method are combined to design the inner loop DMC controller instead of the inner of the cascade DMC-PID control system Loop PID controller.The control scheme is applied to the simulation of superheated steam temperature system with actuator saturation constraints.Simulation results verify the effectiveness of this scheme.