Performance Analysis And Improvement Research Of Pneumatic Valve Positioning Device

Regulating valve,as an actuator in industrial control,is the key and weak link of process control.The hardware characteristics and control algorithm of the valve positioner have a crucial impact on the control performance of regulating valve.In recent years,piezoelectric intelligent positioners tend to replace nozzle baffle mechanical positioners due to their low carbon and intelligent characteristics.However,domestic technology starts relatively late,and there is still a large gap between the domestic and international levels,especially in system performance analysis and control algorithms.Based on domestic and foreign literature and our previous work,researches are conducted as follows:(1)The dynamic modeling and analysis of pneumatic actuator were carried out.First,introduce the composition of the intelligent valve positioning device and analyze its working principle.Then,analyze the nonlinear characteristics of the piezoelectric valve intake and output.And with the help of Newton’s second law,the law of conservation of mass and the law of conservation of energy,the thermodynamic equation of the pressure change of the regulating valve cylinder and the dynamic model equation of the valve stem are established.Finally,the model is analyzed to obtain its performance indicators,and the valve stem control problem is summarized as an optimal control problem.Due to the unknown parameters caused by the uncertain disturbance force and the different characteristics of the regulating valve caused by the assembly process of different regulating valves,there is no guarantee that the positioning device is universal and the characteristic parameters of the regulating valve are introduced.(2)To improve the accuracy,rapidness and universality of pneumatic regulating valve control,this chapter proposes an optimal control strategy based on parameter tuning on the basis of analyzing the influence factors of five-step switch control strategy and positioning device.First,analyze the traditional five-step switch control strategy and the influencing factors of the positioning device,which lays the foundation for the design of the control strategy.Then,the introduced regulating valve characteristic parameters are tuned.Specific parameters include stroke type,minimum start PWM(Pulse Width Modulation),maximum speed and its overshoot,reference speed and reference speed PWM,ensuring the universality of the control strategy.Next,through the optimal control strategy,the entire control process is re-divided into 7 intervals,and measures such as speed valve position and switching point adaptive processing are introduced.Finally,the characteristic parameters tuned by the pneumatic regulating valve are applied to it,so as to improve the accuracy,rapidity and versatility of the control of the pneumatic regulating valve.(3)To verify the effectiveness of the control strategy,this chapter builds an intelligent pneumatic regulating valve performance testing device,and tests and analyzes the pneumatic regulating valve that contains the intelligent positioner.First,an intelligent pneumatic regulating valve performance testing device is built.The device adopts manual step,automatic step and sine curve to test the tracking characteristics of the regulating valve,which can realize multi-mode regulating valve performance evaluation.Then,design experiments with small opening,large opening and full stroke respectively to compare the control effects of positioners at home and abroad.The experimental results show that the control strategy shortens the system adjustment time,improves the valve position control accuracy,and avoids overshoot and oscillation.Finally,the working experiment of four way regulating valve is designed,and the migration characteristics of its position accuracy index are deeply analyzed,which provides help for the design of control strategy.