Development Of New Electric Valve Actuator And Research On Its Precision Positioning Control Strategies

Electric valve is an important equipment for fluid control in the process industry,and its positioning accuracy directly affects the regulation of the fluid.According to the accuracy class,it can be divided into two types,one is the domestic ordinary electric valves represented by the ZJKV with 100 operation steps,which are widely used in the single loop control system.Another is the high-precision electric valve represented by the NelesACE with 20000 operation steps.Due to the high level import cost,the NelesACE is only used in a few special applications.Pharmaceutical production,paper-making,and chemical process require two or more kinds of fluids to be accurately proportioned,and the operation steps is required from 500 to 800 or higher.However,ZJKV cannot meet the accuracy requirements,and the price of NelesACE is not appropriate.There is no intermediate product with suitable technical and economic indicators in the market at present.To solve the problems mentioned above,this paper designed a new electric valve actuator and researched on precision positioning control strategies.Then the actuator was installed on existing valve’s body to form the valve prototype.Aiming at the positioning accuracy is improved to more than 800 operation steps.The main contents of this paper are as follows:(1)Development of new electric valve and research on its design schemeBy exploring the positioning characteristics of electric valve,the main factors limiting the accuracy improvement were the mechanical characteristics of asynchronous motor,the open-loop control characteristics of electric valve,and the mechanical clearance of transmission system.The scheme using a brushless DC motor as driver was determined,and a closed-loop control system under the speed mode was designed based on the LY-F2 controller.Then the development of the new electric valve actuator and the construction of valve prototype were completed.(2)Resear-ch on the precision positioning control algorithmOn the basis of studying the characteristics of trapezoidal speed curve and seven-segment S-shaped speed curve,the five-segment S-shaped speed curve was selected to describe the movement regulation of electric valve,and the function of driving control parameters and speed curve was determined under different execution time.It was found that when the execution time was 100s,the five-segment S-shaped speed curve could shorten the minimum operation step from 0.9° to 0.069°,and achieved 13 times the corner subdivision.The program design process of positioning control algorithm was described in detail.(3)Research and realization of compensation control strategyThe reason of mechanical clearance was analyzed,and it was necessary to implement compensation control strategies under the condition of correctable wear.The data was carried out by the error calibration experiment platform.The return error could be recorded by 124 counts of the encoder on the valve rod side,and the extended time by 1.5s could eliminate the return error.The mathematical model of compensation control was established,and the valve prototype was taken as an example to illustrate the program design process of compensation control and the realization of compensation control strategy.(4)Precision test and application of the valve prototypeBy the test of corner time characteristics of the valve prototype and ZJKV,it was found that the valve prototype had a better linear relationship,and the effective action time was shortened from 2s to 0.2s getting 10 times subdivision.A torque simulation test was performed to verify that the valve prototype had a self-resetting function and could resist the impact of external torque.By the fluids control experiment,it was found that the valve prototype could avoid the flow deviation caused by the mechanical clearance,and verified the application effect of the compensation control system.The valve prototype was used in the high-speed tissue paper machine’s flowing section.It was found that 58 peaks and 49 troughs of the concentration regulation process were reduced within 600s,and the error of the concentration was reduced from 6.32%to 2.89%.The application of positioning control algorithm and compensation control technology made electric valve show more stable regulation effect.This paper improved the structure and control method of electric actuator based on the ZJKV,especially focused on the precision positioning control algorithm and compensation control strategy,and constructed a valve prototype.The test results showed that the valve prototype had 1000 operation steps,and the whole structure could be compatible with ZJKV.As the intermediate product between ordinary and high-precision electric valve,the valve prototype has certain substitution and market promotion value,and it will be expected to provide theoretical support and technical reference for the industrial upgrading of electric valve.