Pneumatic Smart Valve Positioner Design And Implementation

Pneumatic valve has been widely used in large-scale process control such as petroleum, chemical, textile, metallurgy and pharmaceutical because of its advantages of simple structure, convenient manipulation, reliable operation, easy maintenance, fireproof and explosion-proof. Intelligent pneumatic valve positioner (PVP) is the most important accessory of control valve. It can improve the character of valve, enhance the precision and speed of control and increase the flexibly of control.In industrial applications, the requirement of control process is more and more strict, the request of performance towards intelligent PVPs is higher and higher accordingly. The pneumatic actuator has the characteristics of nonlinear, time-variation and time delay and it is widely used in the industrial environment with multi-disturbance. So the PVP with the traditional control algorithm-PID cannot achieve higher request of performance.In order to improve the performance of intelligent PVPs and realize the localization and industrialization of intelligent PVPs, the overall solution, soft-hardware realization and the control programming have been studied in this dissertation which takes the development and reform commission (NDRC)"special project of information technology progress and industrial upgrading" as application background, aiming at the characteristics of nonlinear of the pneumatic actuator. The main work and contributions of this paper are as follows:1.The paper takes the pneumatic actuator as the research object, analyses the control characteristics and establishs the mathematical model. Then a overall control solution of intelligent PVP is proposed, which takes a low-power MCU MSP430as the main core of the controller, and the industrial field4-20mA current as the power, and the HART protocol as communication method. The implementation pricinple of critical circuits is also given in this dissertation.2.Combined with the analysis of the I/P convertor’s characteristics, a novel nonlinear adaptive PID control algorithm is proposed, in which the gain is nonlinear and the integration and derivative constants are adaptive. The experiment result shows that this algorithm is simple and more adaptive in many valves, and could meet the requirement of industrial production.3.According to the requirement of the industrial field configuration control, a simple but effective flow control method based on feedforward mathematical transformation is proposed. A concise human-machine interface with simple control keys is desgined. The communication port and software of HART protocol is implemented.The third-party test results of a professional company shows that the intelligent PVP designed in this paper has achieved the expectation in the repsects of the stable precision, dynamical response, antijamming capability of air supply and load and so on.