Research On Nonlinear Characteristics And Algorithm Of Intelligent Valve Positioner

Pneumatic control valve is applied to many fields of industry and is an important execution component in industrial production process.Intelligent valve positioner is a good guarantee for the control valve to have good control precision and improve the response speed of the valve.The domestic valve positioner has a big gap in control effect compared with foreign products,and there is still much room for improvement in various performance indicators.The domestic research on the control algorithm of intelligent valve positioner is not deep enough.The main reason is that the research on the control valve is not deep enough.Few studies have analyzed the relationship between the control algorithm and the nonlinear characteristics of the valve positioner.Based on the analysis of the core components of the valve positioner: the structure and working principle of the torque motor with nozzle-baffle structure and the pneumatic amplifier structure,the mechanism model of the intelligent valve positioner with nonlinear characteristics is established through experiments and system identification tools.It is found that the saturation nonlinear curve mainly occurring on the torque motor changes with the change of the air pressure of the air source.It is found that the saturated nonlinear curve mainly occurring on the moment motor changes with the change of air pressure.It is found that the joint action of the moment motor and the pneumatic amplifier leads to the backlash characteristics of the valve positioner and the backlash characteristics of the pneumatic actuator caused by friction.The dynamic mathematical model of the control valve established by our laboratory for the first time in the world has been further modified.The control valve model(CVM model)is validated by experiments.The control algorithm is further studied for the nonlinear characteristics of the valve positioner itself.Through the simulation analysis of the modified algorithm,the IMC-PID control algorithm and the parameter tuning rules are selected after comparing the results of the response curve.For the saturated nonlinearity,the Bang-bang/PID piecewise controller is proposed to eliminate the possible integral saturation phenomenon of the PID controller through the piecewise controller.The Bang-bang control makes the controller have the fastest response rate.The response rate of the valve positioner always works in the linear range of the valve positioner when the deviation signal is very small and the appropriate limit value is added.The simulation and experimental results show that the piecewise Bang-bang/PID controller can make the controller have a good output function.For the backlash characteristics of valve positioner and control valve,the backlash compensation algorithm is used to eliminate the backlash characteristics.Experiments show that the valve positioner with backlash compensator can increase the rapidity of the system without affecting the stability of the valve positioner.The backlash compensator also effectively improves the backlash characteristics of control valve and properly improves the rapidity of control valve system.