Closed-loop System Performance Assessment Considering The Characteristic Of The Valve

Most of the practical processes such as smelting industry,chemical industry and sewage industry and etc contain the valve devices.However,greater stiction of the valve will become more and more obvious due to the increased frequency of using valve and insufficient maintenance to the valve and etc.The greater stiction could result in the limit cycle of the process and the oscillation of the system.There will be lots of problems while the system has oscillation:(1)The products will decline in quality and the qualification rate of products will decrease.(2)The wear and tear of the equipment will increase,which will result in increasing the cost of maintenance to the equipment.(3)The consumption of the energy will increase,which causes a certain economic loss.The main topics of the article include valve modeling,oscillation detection and performance assessment of nonlinear system with the valve:(1)Valve modeling:The correction of valve modeling is the foundation of later research.The article has analyzed some faults of the valve proposed by Choudhury and XCH valve model in detail,after which,proposed the modified valve model.(2)Oscillation diagnosis:Firstly,estimating the linear transfer function of the system by using the on-line system identification methods in frequency domain;secondly,determining whether the oscillation comes from the valve by using limit cycle criterion of nonlinear system.(3)Performance assessment of system,the article proposed two system performance assessment methods,namely system performance assessment with oscillation and without oscillation respectively,and illustrated the relationship between them.The nonlinear system is the basic research object in the article,the problems mentioned above were analyzed and tested in the simulations.In practical scenario,the train of thought in this article can be used to analyze the nonlinear system with the valve:firstly,determining the oscillation in the system by the oscillation detection methods;secondly,finding the oscillation source through the oscillation diagnosis methods;finally,obtaining the system performance assessment index observing the running state of the system.