Figure 25 - available via license: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Content may be subject to copyright.
Source publication
In this paper, the current research status of controller performance assessment is reviewed in brief. Solving the problem of proportional–integral–derivative performance assessment usually requires step response data, and several methods are combined and extended. Using the integral of signals, implicit model information contained in process respon...
Citations
... This parameter estimation framework enables to prevent the process output from drifting too far away from the reference signal (setpoint), which is required for many industrial processes. During recent decades, a multitude of derived techniques and methods have been developed 34,35 that have found a great favor of practitioners, especially in chemical and process engineering [36][37][38][39][40][41] . ...
... Forbidden regions are highlighted in red. The circle indicates the position on the dominant complex conjugate pair according to(41). ...
The focus of this contribution is twofold. The first part aims at the rigorous and complete analysis of pole loci of a simple delayed model, the characteristic function of which is represented by a quasi-polynomial with a non-delay and a delay parameter. The derived spectrum constitutes an infinite set, making it a suitable and simple-enough representative of even high-order process dynamics. The second part intends to apply the simple infinite-dimensional model for relay-based parameter identification of a more complex model of a heating–cooling process with heat exchangers. Processes of this type and construction are widely used in industry. The identification procedure has two substantial steps. The first one adopts the simple model with a low computational effort using the saturated relay that provides a more accurate estimation than the standard on/off test. Then, this result is transformed to the estimation of the initial characteristic equation parameters of the complex infinite-dimensional heat-exchanger model using the exact dominant-pole-loci assignment. The benefit of this technique is that multiple model parameters can be estimated under a single relay test. The second step attempts to estimate the remaining model parameters by various numerical optimization techniques and also to enhance all model parameters via the Autotune Variation Plus relay experiment for comparison. Although the obtained unordinary time and frequency domain responses may yield satisfactory results for control tasks, the identified model parameters may not reflect the actual values of process physical quantities.
... Many of these controller evaluation and retuning methods are based on process models. In [3], process data are used to identify a model. Then, the PID controller is designed based on obtained model and desired performance is computed by output prediction. ...
Proportional integral derivative (PID) controllers are the most used in practice for regulatory control. This is due to the good performance achieved by this controller for a variety of processes. However, about 60% have performance issue. This problem can be more evident in multivariable processes, due to the coupling between the loops. One way to improve performance is to retune the parameters. Thus, in this article, a PID control retune technique is presented. Frequency domain data are used to compute gain increments. Identification of the parametric model of the process is not necessary. The method can be applied to multivariable processes with time delay, integrative dynamics, and nonminimum phase zeros. Simulation results and the effectiveness of the method are discussed.
... This parameter estimation framework enables to prevent the process output from drifting too far away from the reference signal (setpoint), which is required for many industrial processes. During recent decades, a multitude of derived techniques and methods have been developed 34,35 that have found a great favor of practitioners, especially in chemical and process engineering [36][37][38][39][40][41] . ...
The focus of this contribution is twofold. The first part aims at the rigorous and complete analysis of pole loci of a simple delayed model, the characteristic function of which is represented by a quasi-polynomial with a non-delay and a delay parameter. The derived spectrum constitutes an infinite set, making it a suitable and simple-enough representative of even high-order process dynamics. The second part intends to apply the simple infinite-dimensional model for relay-based parameter identification of a more complex model of a heating-cooling process with heat exchangers. Processes of this type and construction are widely used in industry. The identification procedure has two substantial steps. The first one adopts the simple model with a low computational effort using the saturated relay that provides a more accurate estimation than the standard on/off test. Then, this result is transformed to the estimation of the initial characteristic equation parameters of the complex infinite-dimensional heat-exchanger model using the exact dominant-pole-loci assignment. The benefit of this technique is that multiple model parameters can be estimated under a single relay test. The second step attempts to estimate the remaining model parameters by various numerical optimization techniques and also to enhance all model parameters via the Autotune Variation Plus relay experiment for comparison. Although the obtained unordinary time and frequency domain responses may yield satisfactory results for control tasks, the identified model parameters may not reflect the actual values of process physical quantities.
In this work, the problem of monitoring the performance of control loops and retuning is addressed. Poor performance of control loops reduces product quality, generates losses and can affect safety in industrial processes. There is a great interest in the industry in the search for methods that are simple to use and interpret. Cascaded control loops are widely used because they mitigate the effect of disturbances and process variations on the controlled variables. The fast dynamics of the inner loop, whose reference is generated by the controller of the outer loop, represents a challenge when one wants to investigate its performance during operation. The methods proposed here are completely data-based, requiring the user only to provide operating data and to approve the performance of the control loops to be monitored, which must always be done in some way. Both monitoring and retuning are validated by statistical tests, reducing the effect of uncer- tainties introduced by noise that is always present in industrial processes. The data used in all steps are generated by applying small disturbances added to the external loop control signal, reducing the deviations of the controlled variables from their references. The methodology is applied to a pilot plant with industrial equipment, and controlled by a distributed control system. A flow loop acts as an inner loop for a level control loop. The obtained results show that the methodology allows successfully attacking the proposed problem, being additionally replicable in industrial environments in general.
