| 1. |
- Andersson, Torbjörn, et al.
(författare)
-
Estimation of Residence Time in Continuous Flow Systems with Dynamics
- 1995
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524 .- 1873-2771. ; 5:1, s. 9-17
-
Tidskriftsartikel (refereegranskat)abstract
- A method for estimation of residence time in continuous flow systems with varying dynamics is presented. By resampling, i.e., choosing time instants different from the given sampling instants, and interpolation between measured data points, we obtain a continuous flow system with constant residence time expressed in the new resampled time vector. We assume the flow patterns in the systems are invariant. The new data set is then used for identification of parameters in a chosen model structure. From the identified model, the residence time is readily calculated and a procedure for that is briefly described. The presented method is readily extended to enable use in recursive identification. In that case, however, as an improvement of tracking ability of an ordinary recursive routine. Keywords : System identification, residence time estimation, time-varying systems, variable flow and/or volume, continuous flow systems, recursive identification.
|
|
| 2. |
- Cui Carlemalm, Hong, et al.
(författare)
-
Performance limitations in decentralized control
- 2002
-
Ingår i: Journal of Process Control. - 0959-1524 .- 1873-2771. ; 12:4, s. 485-494
-
Tidskriftsartikel (refereegranskat)abstract
- In decentralized control of multivariable systems. the system is decomposed into a number of subsystems and individual controllers are designed for each subsystem. Advantages of such decomposition include reduced modelling requirements and case of implementation. However, a potential disadvantage is a reduction in achievable control performance due to restricted controller structure. In this paper we consider performance limitations from non-minimum phase transmission zeros in decentralized control. In particular, we derive conditions on when closing the loop around one subsystem moves transmission zeros of other subsystems across the imaginary axis. Such zero crossings may occur regardless of the existence of non-minmum phase behavior in the open-loop system, and may, therefore, represent performance limitations specific to the use of decentralized controllers.
|
|
| 3. |
- Atta, Khalid, et al.
(författare)
-
Adaptive amplitude fast proportional integral phasor extremum seeking control for a class of nonlinear system
- 2019
-
Ingår i: Journal of Process Control. - : Elsevier. - 0959-1524 .- 1873-2771. ; 83, s. 147-154
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a modification of the fast phasor extremum-seeking control for the fast optimization of a class of Wiener-Hammerstein nonlinear dynamical systems. The proposed technique provides a significant improvement of the closed-loop system's performance. This study introduces a new adaptive amplitude technique that is used to adaptively adjust the perturbation amplitude to a small predetermined value in a neighbourhood of the system's unknown optimal equilibrium. An analysis of the system demonstrates that semi-global practical stability analysis of the overall system to the unknown optimum is achieved. The effectiveness of the proposed approach is illustrated using numerical examples. The approach is also implemented for the optimal operation of a lean burn combustion system.
|
|
| 4. |
- Blackburn, Landen D., et al.
(författare)
-
Dynamic machine learning-based optimization algorithm to improve boiler efficiency
- 2022
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524. ; 120, s. 129-149
-
Forskningsöversikt (refereegranskat)abstract
- With decreasing computational costs, improvement in algorithms, and the aggregation of large industrial and commercial datasets, machine learning is becoming a ubiquitous tool for process and business innovations. Machine learning is still lacking applications in the field of dynamic optimization for real-time control. This work presents a novel framework for performing constrained dynamic optimization using a recurrent neural network model combined with a metaheuristic optimizer. The framework is designed to augment an existing control system and is purely data-driven, like most industrial Model Predictive Control applications. Several recurrent neural network models are compared as well as several metaheuristic optimizers. Hyperparameters and optimizer parameters are tuned with parameter sweeps, and the resulting values are reported. The best parameters for each optimizer and model combination are demonstrated in closed-loop control of a dynamic simulation, and several recommendations are made for generalizing this framework to other systems. Up to 0.953% improvement is realized over the non-optimized case for a simulated coal-fired boiler. While this is not a large improvement in percentage, the total economic impact is $991,000 per year, and this study builds a foundation for future machine learning with dynamic optimization.
|
|
| 5. |
- Borrelli, Francesco, et al.
(författare)
-
Reference Governor for Constrained Piecewise Affine Systems
- 2009
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524. ; 19:8, s. 1229-1237
-
Tidskriftsartikel (refereegranskat)abstract
- We present a methodology for designing reference tracking controllers for constrained, discrete-time piecewise affine systems. The approach follows the idea of reference governor techniques where the desired set-point is filtered by a system called the “reference governor”. Based on the system current state, set-point, and prescribed constraints, the reference governor computes a newset-point for a low-level controller so that the state and input constraints are satisfied and convergence to the original set-point is guaranteed.In this note we show how to design a reference governor for constrained piecewise affine systems by using polyhedral invariant sets, reachable sets, multiparametric programming and dynamic programming techniques.
|
|
| 6. |
- Bortolin, Gianantonio, et al.
(författare)
-
On modelling of curl in multi-ply paperboard
- 2006
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524 .- 1873-2771. ; 16:4, s. 419-429
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a grey-box model for the curl and twist of the carton board produced at AssiDoman Frovi, Sweden. The main equations are based on classical lamination theory of composite materials, and each constituent ply is considered as a macroscopic homogeneous, elastic medium. The model used data from June to September 2004, and shows a general agreement between predicted and measured curvatures. The data were cleaned from outliers by means of the Hampel filter, a nonlinear moving window filter, and with a model based method. Regularization and backwards elimination were used to cope with the low identifiability of the problem. The model was then complemented with a sub-model of immeasurable/unmodelled disturbances estimated with an extended Kalman filter. (C) 2005 Elsevier Ltd. All rights reserved.
|
|
| 7. |
- Castaño Arranz, Miguel, et al.
(författare)
-
On the selection of control configurations for uncertain systems using gramian-based Interaction Measures
- 2016
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524 .- 1873-2771. ; 47, s. 213-225
-
Tidskriftsartikel (refereegranskat)abstract
- critical step in the control design of industrial processes is the Control Configuration Selection (CCS), where each actuator is associated with a set of measurements which will be used in the calculation of the control action.A possible solution to the CCS problem is given by the gramian-based Interaction Measures (IMs), which are derived from nominal process models. This paper introduces the derivation of uncertainty bounds for a gramian-based IM using models with uncertainty described in multiplicative form. An alternative to this model-based approach is presented, where uncertainty bounds are estimated from a tailored experiment.In addition, a procedure for robust CCS is introduced. This procedure integrates the calculated uncertainty bounds in the design of the control configuration.
|
|
| 8. |
- Castano, Miguel, et al.
(författare)
-
New methods for interaction analysis of complex processes using weighted graphs
- 2012
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524 .- 1873-2771. ; 22:1, s. 280-295
-
Tidskriftsartikel (refereegranskat)abstract
- The selection of the structure of a controller in large scale industry processes usually requires extensive process knowledge. The aim of this paper is to report new results on recently suggested methods for the analysis of complex processes. These methods aid the designers in comprehending a process by representing structural and functional relationships from actuators and process disturbances to measured or estimated variables. The methods are formulated in a flexible framework based on graph theory, which can also be used for closed-loop analysis. Additionally, the sensitivity of the methods to scaling and time delays are discussed and resolved. It is also proposed how filtering can be used to restrict the analysis to a frequency region of interest. The feasibility of the methods is shown by the use of three case studies. A quadruple tank process is used to exemplify the methods and their use. Then the methods are applied on a real-life process, the stock preparation plant of a pulp and paper mill. The third study case analyzes a previously published example in closed loop. It is shown that the methods can be used to take efficient decisions on decentralized and sparse control structures, as well as assessing the channel interactions in a closed-loop system.
|
|
| 9. |
- Diehl, Stefan, et al.
(författare)
-
Control of an ideal activated sludge process in wastewater treatment via an ODE–PDE model
- 2013
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 1873-2771 .- 0959-1524. ; 23:3, s. 359-381
-
Tidskriftsartikel (refereegranskat)abstract
- The activated sludge process (ASP), found in most wastewater treatment plants, consists basically of a biological reactor followed by a sedimentation tank, which has one inlet and two outlets. The purpose of the ASP is to reduce organic material and dissolved nutrients (substrate) in the incoming wastewater by means of activated sludge (microorganisms). The major part of the discharged flow through the bottom outlet of the sedimentation tank is recirculated to the reactor, so that the biomass is reused. Only two material components are considered; the soluble substrate and the particulate sludge. The biological reactions are modelled by two nonlinear ordinary differential equations and the continuous sedimentation process by two hyperbolic partial differential equations (PDEs), which have coefficients that are discontinuous functions in space due to the inlet and outlets. In contrast to previously published modelling-control aspects of the ASP, the theory for such PDEs is utilized. It is proved that the most desired steady-state solutions can be parameterized by a natural control variable; the ratio of the recirculating volumetric flow to the input flow. This knowledge is a key ingredient in a two-variable regulator, with which the effluent dissolved nutrients concentration and the concentration profile in the sedimentation tank are controlled. Theoretical results are supported by simulations.
|
|
| 10. |
- Ding, Limei, et al.
(författare)
-
Application of reduced models for robust control and state estimation of a distributed parameter system
- 2009
-
Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524 .- 1873-2771. ; 19:3, s. 539-549
-
Tidskriftsartikel (refereegranskat)abstract
- This paper studies the application of reduced models of a distributed parameter system for robust process control and state estimation. We take the approach of integrating model reduction, parameter identification, and model uncertainty analysis, in purpose to find an appropriate trade-off between complexity and robust performance. The application example is the temperature system in a continuous paper pulp digester. Physical modeling of this process results in coupled linearized partial differential equations which are then reduced into low-order nominal process models using an orthogonal collocation approximation method.Two different approaches to obtaining a model uncertainty description are adapted for use on a distributed parameter system with low-order nominal model and shown to produce similar results when tested with measurement data. It is also demonstrated how this uncertainty description, in combination with the reduced model, may be used for robust control design and verification of the control performance on the distributed parameter system.Finally, the possibility of estimating the distributed process state using a state observer for the reduced process is demonstrated. Measurements of the process state in a certain position is available and is shown to agree with the estimated state at the same position.
|
|
