Valve Stiction Control Based On The Novel Two-step Method

Industrial loop oscillation problems seriously impact the economic efficiency of enterprises. In order to discover and solve the oscillation problems it is necessary to study oscillation monitoring, oscillation control and compensation. Studies have shown that20%to30%of the control loop oscillation caused by the control valve. The stiction property of control valve is the most common non-linear characteristics. It affects the performance of the control system. Stiction is also one of the most difficult problems to overcome in the valve. It will cause the control loop oscillation, lead to product quality decline, increase energy consumption and accelerate equipment wear and so on. Currently, many scholars have study valve stiction in control loop, and have made a lot of research. This thesis will study the valve stiction characteristics in depth, included the following three parts:1. Firstly this thesis introduces stiction model. It elaborates stiction characteristics modeling method from two aspects:the mechanism model and data-driven model. Currently there are mainly two valve stiction models:the traditional physical model and the Kano model, but they all have their own limitations. This thesis uses a simple model which captures the essential features to simplify some of the details of the stiction of the dynamic characteristics, and this model is similar to the Kano model, only two parameters, but the structure is much simpler and the magnitude of the stiction can be quantified.2. The traditional two-step method has several limitations and there are great difficulties to apply this method to the actual industry, and the valve position of the two-step method is unpredictable. With the development of production processes and measurement techniques, now more and more control valves can be measurable from the unpredictable. In this thesis, a new two-step method to control the valve stiction is proposed. The control valve output can be measured in order to overcome the limitations of the traditional two-step method. This paper combines predictive PI control algorithm and stiction control Organically, introduces control algorithm in details, analyzes when the loop exists stiction, how to overcome the oscillation and gives control parameter setting method and so on. At last OPTO22the PAC project-based monitoring software simulation, simulation results show that the effectiveness of the proposed research method.3. In order to apply this new two-step method to actual industry, a set of real-time monitoring HMI is developed in this paper which is based on OPTO22the PAC project monitoring software. Users can change various parameters on the controller interface directly, so users can clearly see that changes of different waveforms at the same time. The HMI is simple, convenient and practical.