A Method Of Control System Performance Evaluation Based On The Cloud Theory

Industrial process controllers can’t achieve the design performance and even seriously deteriorate after a long time run. The reasons include changing (time variant) process operating conditions, process nonlinearities, unknown external disturbances and change/problems associated with instrumentation and equipment. The presence of these uncertainties increases the difficulty of the Qualitative and quantitative integration in the assessment process. Without timely monitoring of performance and take effective measures to repair the controller, it will reduce the economic efficiency of the control system. In recent years, the research of control performance assessment has attracted increasing attention. However, there are still some unsolved problems in this research area, which limits the industrial applications of performance evaluation techniques. current research of the control system performance assessment focuses on the controller optimization, this paper from the uncertainty in the control system starting, the introduction of Li Deyi academicians cloud theory to express the uncertainty in the control system, take full advantage of the fuzziness and randomness of the information, completion of the mapping between the qualitative and quantitative, make assessment results more intuitive. This paper includes:(1) The review of the current research status and development trends in control performance assessment (CPA) technology is presented. And the factors that affect the CPA are synthetically analyzed.(2) The minimum variance benchmark which is the most extensive useful performance evaluation method is introduced in this paper. The minimum variance benchmark can provide a practical reference to the performance of control systems, and this method only need the routine data and the time delay of the process. And the evaluate methods for single loop and multivariate control systems are introduced in this paper. The results of the simulation show that these methods are available in performance evaluation.(3) A review is presented of cloud theory of history, research status and development trends, and introduces the basic concepts of the cloud theory and its generation method and basic computing.(4) Cloud theory is applied in single variable control systems. Expression system output data with a one-dimensional cloud model, and come to the cloud visual display characteristics of the data. By the similarity comparison with the standard cloud and the test cloud can visually determine the status of the system. Compared with the evaluation method of minimum variance by simulation proves assessment of the cloud theory is valid. Motor control system as an example to further illustrate the application of the performance assessment methods based on the cloud theory in the actual control system, and to prove its effectiveness.(5) Cloud theory application in multi-loop control system. The concept "multi-dimensional cloud" is introduced. Express each control loop with a one-dimensional cloud model, multi-dimensional cloud model is the synthesis of one-dimensional cloud model. By comparison of the multi-dimensional cloud model between test cloud model and standard cloud, we get the similarity coefficient, then to arrive at the results of the assessment of system performance. Prove the effectiveness of the method through simulation.