Process frequency response estimation from relay feedback
ABSTRACT In this paper, a method for process frequency response identification is proposed, which can identify multiple points on process frequency response from a single relay feedback test. The process input and output transients resulting from a relay feedback cannot be directly converted to the frequency domain to obtain a process frequency response using FFT. A decay exponential is then proposed to modify the process input and output, so that the process frequency response can be identified with the help of FFT. Real-time testing of the method on various processes gives quite accurate process frequency responses, especially in the frequency range [0, ωc], which is important for control design and process modelling. The method inherits and extends the advantages of the original relay auto-tuning technique. It can be easily applied to PID auto-tuning and to transfer function modelling.
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ABSTRACT: In this paper, a new identification method performed in the time domain based on the decentralized step-test is proposed for two inputs and two outputs (TITO) processes with significant interactions. In terms of parameter identification, the coupled closed-loop TITO system is decoupled to obtain four individual single open-loop systems with the same input signal. As in the SISO case, new linear regression equations are derived, from which the parameters of a first- or second-order plus dead-time model can be obtained directly. The proposed method outperforms the existing estimation methods for multivariable control systems that use step-test responses. Furthermore, the method is robust in the presence of high levels of measurement noise. Simulation examples are given to show both effectiveness and practicality of the identification method for a wide range of multivariable processes. The usefulness of the identified method in multivariable process modeling and controller design is demonstrated.Asian Journal of Control 05/2005; 7(2):154 - 162. · 1.41 Impact Factor
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ABSTRACT: Step and relay feedback tests have been widely used for model identification in the process industry. The corresponding identification methods developed in the past three decades are surveyed in this paper. Firstly, the process models with time delay mainly adopted for identification in the literature are presented with a classification on different response types. By categorizing the major technical routes developed in the existing references for parameter estimation relating to different applications, the identification methods are subsequently clustered into groups for overview, along with two specific categories for robust identification against load disturbance and the identification of multivariable or nonlinear processes. The rationales of each category are briefly explained, while a typical or state-of-the-art identification algorithm of each category is elucidated along with application to benchmark examples from the literature for illustrating the achievable accuracy and robustness, so as to facilitate the readers to have a general knowledge of the research development. Finally, an outlook on the open issues regarding step or relay identification is provided to call attention to future exploration.Journal of Process Control 11/2013; 23(10):1597-1623. · 2.18 Impact Factor
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ABSTRACT: One of the important parameters for tuning the response of a system in closed loop is the decay ratio. In this paper three tuning methods are compared: the DRMO tuning method [15,16], the KT tuning method  and the non-convex tuning method [3,17]. The latter method is based on setting the value of maximum sensitivity function M s . The results have shown, that the DRMO method sets a closed-loop response such, that the decay ratio is within a relatively tight interval with regard to other two methods, despite the fact that the DRMO method isn't based on optimization procedure (as is the case with non-convex method).