Intelligent Control And Analysis Of Piezoelectric Switch Valve Positioner

Pneumatic valve positioner is widely used in chemical industry,energy,oil and gas,water treatment,paper industry and other industrial fields.The type of foreign valve positioner has been transferred from mechanical and electronic to intelligent electronic.The intelligent valve positioner include three types: nozzle type,piezoelectric switch type,and piezoelectric proportional type.Among them,the piezoelectric switch type valve positioner has the advantages of low power consumption,low gas consumption,strong anti-interference ability and high precision,which has been widely promoted.However,the domestic research on valve positioner research started late,the technology is relatively backward,the failure rate is high,and the adjustment accuracy and speed are quite different from the foreign products,resulting in the market share of the valve positioner is relatively small,and mainly concentrated in the low-end market.The main reason that affects the performance of domestic valve positioners is due to the immature control algorithm.Therefore,in order to increase the market share of domestic valve positioners,and to introduce domestic valve positioners into the high-end market,it is necessary to study the control algorithm of valve positioner.On the basis of consulting and analyzing a large number of documents,this paper has carried out the following work in the intelligent control and analysis of piezoelectric switch valve positioner:(1)The working principle of the piezo-switched intelligent valve positioning system is analyzed in detail.With the help of Newton's second law,the law of conservation of mass,and the law of conservation of energy,a detailed mechanism modeling and analysis of the pneumatic intelligent valve positioning system was performed.During this process,the mechanism model of piezoelectric valve,the mechanism model of pneumatic control valve and the flow output mechanism model of pneumatic control valve are established.(2)The experimental platform of intelligent valve positioning system is built,and a large number of performance tests are carried out,and these tests provides guidance for the design of control algorithm.The influence of the pressure difference between the cylinder pressure and the air source pressure(differential pressure for short)on the intake rate of the piezoelectric valve is analyzed.It is concluded that the choice of PWM duty cycle should be related to the valve position.it also analyzes the influence of PWM duty cycle on the valve position response curve,and concludes that PWM duty cycle is in a positive proportion to the valve position operation speed and in a negative proportion to the regulation time.(3)Based on the analysis of the traditional five-step switch control algorithm,an improved control algorithm and a new parameter auto-tuning method are proposed.All control parameters in the improved control algorithm are obtained by self-tuning,which improves the universality of the algorithm.The parameter self-tuning method can automatically identify the stroke type,end position,maximum overshoot,optimal PWM duty ratio of different valve positions and other parameters,which provides the basis for the control parameter selection of the improved control algorithm.The control algorithm was implemented and verified with the help of an experimental bench.The experimental results show that the improved control algorithm not only greatly reduces the valve position adjustment time,but also avoids the overshoot phenomenon in the whole stroke range.(4)Considering the mechanical principle of the valve positioning system and the matching of the positioner parameters,the reasons for the oscillation phenomenon of the regulating valve during the regulation process are analyzed,and the corresponding strategies are given.Through theoretical derivation,the valve positioning system is found to be a second-order time-varying system with natural oscillation characteristics.A large number of simulation experiments are carried out to analyze the impact of friction on the system performance and provide guidance for the control valve packing.The oscillation problem caused by the mismatch between the parameters of the PID controller and the positioner of the process control system is analyzed.