Font Size: a A A

Minimum Variance Performance Assessment Of Control Systems Under Loop Osclllation

Posted on:2020-06-22Degree:MasterType:Thesis
Country:ChinaCandidate:T LiFull Text:PDF
GTID:2428330578466937Subject:Control theory and control engineering
Abstract/Summary:PDF Full Text Request
In the actual industrial field,oscillation in control loop of is very common.The root causes of oscillation of the closed-loop system mainly are:(1)external causes of the system(such as periodic external disturbances);(2)non-linearity of the system itself(such as valve stiction);(3)poor parameter setting of the controller or poor design of the control system;This paper mainly studies the performance accessment of the first two oscillation sources.At present,researches on the performance accessment of minimum variance are limited within the stationary output data driven by white noise.However,in the actual industrial field,the process output signal doesn't satisfy such assumption,especially in the case of loop oscillations.When the closed-loop system behaves non-stationary characteristics,the traditional performance accessment method is no longer applicable.Valve nonlinear characteristics including valve stiction,often lead to limit cycle and self-excited oscillation.According to a survey on process industry,about 20-30%of loop oscillations are caused by valve stiction.The main research contents of this paper include the following two aspects:(1)when the closed-loop system oscillates due to the interference of periodical signals.The empirical mode decomposition(EMD)method is used for signal separation of non-stationary output signals to obtain stationary random signal and the minimum variance performance assessment benchmark can be solved based on it.In addition,the k-step difference method can also be used to process the non-stationary output signal.The improved FCOR algorithm(for Filtering and CORrelation analysis)is then used to calculate the minimum variance assessment benchmark.(2)when the closed-loop system generates self-excited oscillation due to valve stiction.First,the nonlinear components in the output signal are removed by EMD separation method,and the minimum variance value is estimated by using the remaining linear random signals.Then,the linear identification method is used to identify the valve stiction characteristic,that is linear fitting,and based on the linear model,the estimated minimum variance benchmark is corrected.
Keywords/Search Tags:Performance accessment, Minimum variance, Empirical Mode Decomposition, Non-stationary, Valve stiction nonlinearity
PDF Full Text Request
Related items