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Control Performance Assessment Of Time-varying System

Posted on:2020-04-02Degree:MasterType:Thesis
Country:ChinaCandidate:R XuFull Text:PDF
GTID:2428330578464182Subject:Control Science and Engineering
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As the brain of industrial production process,whether it is conventional PID control or advanced control,the characteristics of each link of the control loop may change over time,such as sensor or detection device failure,equipment aging,etc.The control performance of the controller will decline compared with the initial operation of the controller.If the performance degradation can not be monitored and adjusted in time,it will bring huge economic losses and waste.In this context,it is of great significance to assess the performance of the control system and maintain its good control level.Control Performance Assessment(CPA)has attracted wide attention in the past decade.However,there are still some unsolved problems in this field,which limits the wide application of performance assessment technology in the actual industrial process.Most of the research on control performance assessment focuses on time-invariant systems,but relatively few on the widely existing time-varying systems.On the basis of previous studies,the performance assessment of time-varying systems is studied in this paper.The main contents are as follows:(1)This chapter analysed the most commonly used method of performance assessment of control system,that is,a method of minimum variance control performance assessment.The method compares the output variance of the system under the action of the minimum variance controller with the actual output variance of the system,and obtains the Harris index to assess the performance of control system.At the same time,the performance assessment method based on generalized minimum variance control is introduced.This method is an improvement of the performance assessment method of minimum variance control,taking into account the constraints of control effect,and introducing the output variance of the controller into the performance benchmark.(2)For the case of PID control system with time-varying disturbance,a performance assessment method of PID achievable minimum variance control based on Multi-model weighting is proposed.Firstly,a sub-PID achievable minimum variance controller is designed according to the characteristics of each disturbance.Then,a weight is constructed based on the disturbance action time to design a multi-model weighted controller.Then,the minimum variance of the system output under the action of the controller is used as a benchmark to assess the performance of the PID control system.This method takes into account the characteristics of each disturbance accurately and can effectively assess the performance of time-varying disturbance control system.(3)For control systems with time-varying disturbances,a performance assessment method of generalized minimum variance control is proposed.First,we keep the actual output signal of the control system stable in the presence of the abrupt disturbance.Then,a benchmark controller is obtained under the objective of minimizing the variance of the generalized output signal of the control system.The generalized output signal variance when this benchmark controller is working is used as a benchmark to assess the control performance of the time-varying disturbance system.(4)For the case of time-varying process in the control loop,a performance assessment method based on PID achievable minimum variance is proposed.Firstly,the time-varying parameters of the process are estimated.Then,the weight is set based on the PID achievable minimum variance,and then a weighting function is constructed.By solving the minimum value of the function,a global optimal benchmark controller is obtained.The variance of the system output under the controller is used as a benchmark to assess the performance of the controller.
Keywords/Search Tags:performance assessment, time-varying system, PID achievable minimum variance, multiple-model weighted, generalized minimum variance
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