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- Eriksson, Karin, 1976, et al.
(författare)
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A note on decoupling
- 2009
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Ingår i: Proceedings 15th Nordic Process Control Workshop. ; , s. 36-37
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 18. |
- Eriksson, Karin, 1976, et al.
(författare)
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Internal interconnections impact on control performance in a thermomechanical pulping process
- 2014
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Ingår i: 2009 10th European Control Conference, ECC 2009; Budapest; Hungary; 23 August 2009 through 26 August 2009. - : IEEE. ; , s. 3486-3491
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Konferensbidrag (refereegranskat)abstract
- Process integration may indeed be advantageous, particularly in a plant-wide economical sense, but there is also a potential risk that unnecessary difficulties are introduced when it comes to process control. This work identified several internal interconnections in a thermomechanical pulp refiner line as a result of an integration approach adopted during the process design. Firstly, a disturbance sensitivity analysis for the overall production process is carried out. Secondly, a simulation model is constructed and using real process data it is found to successfully reflect the complex dynamic behavior observed at the actual plant. The simulation model can provide indications on how the process performance can be improved by process design modifications. The results suggest that the presence of internal interconnections increases the demands on the control system and also set limits for its performance. If control aspects had been considered at the earliest stages of process development, the possibility to achieve satisfactory process performance could have been significantly improved.
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- Henriksson, M., et al.
(författare)
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Model-based on-board turbofan thrust estimation
- 2011
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Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661. ; 19:6, s. 602-610
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Tidskriftsartikel (refereegranskat)abstract
- In this article model-based thrust estimation for turbofan engines is discussed. Two different model-based thrust estimation filters are applied to a low bypass ratio turbofan engine. The two estimators are based on a simple gross thrust model and on a thermodynamic semi-transient model, respectively. The filter parameter estimation as well as the corresponding validation of parameters is based on the use of the "leave one out cross validation" technique. In this article it is demonstrated, in particular, that a thrust estimation filter based on the thermodynamic semi-transient engine model(1) shows good accuracy and predicts the transient thrust and static measurements very well.
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- Olesen, Veronica, 1975, et al.
(författare)
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Closed loop model reduction applied to a tank reactor process
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this article is the direct assessment of model simplification from a feedback control perspective. Normally, dynamic systems are simplified dimensionally and structurally from an open loop perspective. In spite of the intentions, the resulting models often tend to be unnecessary complex for controller design and synthesis anyway. Here, a four step method is proposed that incorporates a feedback controller, and makes use of the closed loop sensitivity functions to indicate significant impact on the closed loop behaviour from a performed model simplification. The method is applied to a first order reaction in an ideally stirred tank reactor with a cooling system. For this system a general detailed model is derived. The model includes temperature dependent parameters such as specific heats and densities. This reference model is locally unstable in most operating points, making open loop simplification impractical. The proposed closed loop simplification method makes it possible to evaluate which approximations of the system that can be justified.
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| 35. |
- Olesen, Veronica, 1975, et al.
(författare)
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Closed loop model reduction applied to a tank reactor process
- 2008
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 63:3, s. 674-684
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Tidskriftsartikel (refereegranskat)abstract
- The subject of this article is the direct assessment of model simplification from a feedback control perspective. Normally, dynamic systemsare simplified dimensionally and structurally from an open loop perspective. In spite of the intentions, the resulting models still often tendto be unnecessary complex for controller design and synthesis. Here, a four step method is proposed that incorporates a feedback controller,and makes use of the closed loop sensitivity functions to indicate significant impact on the closed loop behaviour from a performed modelsimplification. The method is applied to a first order reaction in an ideally stirred tank reactor with a cooling system. For this system ageneral and detailed model is derived. The model includes temperature dependent parameters such as specific heat capacities and densities.This reference model is locally unstable in most operating points, making open loop simplification impractical. The proposed closed loopsimplification method makes it possible to evaluate which approximations of the system that can be justified.
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- Olesen, Veronica, 1975, et al.
(författare)
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Quantitative assessment in frequency domain of reactor model simplification
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this report is to investigate when and how different approximations can be applied to a continuous stirred tank reactor system. A complex first principles model of a first order exothermic reaction, taking place in the reactor, is used as a reference model. A large number of different sets of substances, described by different physical properties, are tested. For each set of substances, a number of approximations leading to model simplifications are tested in closed loop. The results of the investigation are properties to be fulfilled for each approximation to be appropriate. The resulting simplified model equations are also explicitly presented.
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- Olesen, Veronica, 1975, et al.
(författare)
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Tank reactor temperature control using Quantitative Feedback Theory
- 2008
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Ingår i: Proceedings 17th IFAC World Congress.
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Konferensbidrag (refereegranskat)abstract
- Temperature control of tank reactors with exothermic reactions is an acknowledgedly difficult task because of complex interacting phenomena, several nonlinearities and unstable dynamics. Traditionally, simple control functions are implemented, implying poor control performance and small operating windows. On the other hand many advanced control schemes have been published, though they rely on, in many applications, too simplistic process models. Here, a control strategy using only a small number of linear controllers has successfully been applied to a rigorous reactor model, including the cooling system dynamics. The methodology is to first linearize the model in steady-state and relevant non-stationary points and let the resulting models define uncertainties in the frequency plane. Then Quantitative Feedback Theory (QFT) is used to ensure that robust feedback system specifications are fulfilled for all these uncertainties.
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| 41. |
- Pinares, Gustavo, 1981, et al.
(författare)
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Analysis of the dc dynamics of VSC-HVDC systems using a frequency domain approach
- 2013
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Ingår i: 2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC). - : IEEE Computer Society. - 2157-4847 .- 2157-4839. - 9781479925223 ; , s. 6837285-
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Konferensbidrag (refereegranskat)abstract
- In this paper, the dc dynamic performance of VSC-HVDC systems is investigated using the frequency domain approach. In a previous work, it has been found through the eigenvalue analysis that, in some situations, the VSC-HVDC system becomes unstable when the converter which controls the direct-voltage injects power exceeding a certain value. However, the cause of the instability was not addressed. This paper attempts to answer some of the remaining questions in the previous work through the frequency response of the elements that compose the system. In order to facilitate the analysis, appropriate assumptions have been made. The transfer function of both, dc grid and the converter which controls the direct-voltage, are derived. The results from the analysis show that, depending on the direction of the power, the frequency response of the converter has a negative resistance characteristic which amplifies resonances in the dc grid.
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| 42. |
- Pinares, Gustavo, 1981, et al.
(författare)
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On the analysis of the dc dynamics of multi-terminal VSC-HVDC systems using small signal modeling
- 2013
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Ingår i: 2013 IEEE Grenoble Conference PowerTech, POWERTECH 2013; Grenoble; France; 16 June 2013 through 20 June 2013. - 9781467356671 ; , s. Art. no. 6652303-
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Konferensbidrag (refereegranskat)abstract
- In this paper, an analysis of the dc dynamics of multiterminal VSC-HVDC systems using the small signal modeling method is presented. Usually, the VSC controllers are designed under the consideration that they operate independently of each other. However, the possible interactions among them and the dc grid should be studied, especially in multi-terminal topologies. In this paper, three VSC-HVDC systems are modeled and, after linearization, the eigenvalues of the system are calculated for different loading conditions. The results from this analysis are compared to those obtained from more detailed models using PSCAD. It is shown that the operating point, the gains of the direct-voltage controller and the cable dynamics have an impact on the system performance.
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| 45. |
- Rutquist, Per, 1976, et al.
(författare)
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Finite-time state-constrained optimal control for input-affine systems with actuator noise
- 2011
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902661937 ; 18:PART 1, s. 5915-5919
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Konferensbidrag (refereegranskat)abstract
- Abstract: We show that a linearizing transformation of the Hamilton-Jacobi-Bellman (HJB) equation can be applied to certain finite-time problem such that the time dependence can be separated and also has a simple analytical solution. The remaining state dependence is the solution to a linear eigenvalue problem that may have an analytical solution or is readily solved numerically. The efficiency of the method is illustrated by an inventory control problem.
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| 46. |
- Rutquist, Per, 1976, et al.
(författare)
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On the infinite-time solution to state-constrained stochastic optimal control
- 2008
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 44:7, s. 1800-1805
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for solving the infinite time Hamilton-Jacobi-Bellman (HJB) equation for certain state-constrained stochastic problems. The HJB equation is reformulated as an eigenvalue problem, such that the principal eigenvalue corresponds to the expected cost per unit time, and the corresponding eigenfunction gives the value function (up to an additive constant) for the optimal control policy. The eigenvalue problem is linear and hence there are fast numerical methods available for finding the solution.
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| 47. |
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| 48. |
- Rutquist, Per, 1976, et al.
(författare)
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Optimal Control of a Batch Reactor Using the Linearized Hamilton-Jacobi-Bellman Equation
- 2012
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Ingår i: Proceedings 15th Nordic Process Control Workshop. - 9788764309461 ; , s. 187-188
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- AbstractIn this work we present an efficient method for solving an optimal control problem for a batch reactor, where a temperature dependent exothermic reaction takes place within a preset duration and within specified temperature bounds. The Hamilton-Jacobi-Bellman (HJB) equation corresponding to the optimal control problem is nonlinear and has infinite boundary conditions due to the state constraints (bounds on temperature and concentration),which makes it troublesome to solve. However, using a logarithmic transformation, the HJB-equation is transformed into a linear partial differential equation with zero boundary conditions.Furthermore, the problem can then be solved using variable separation such that the time-dependent part has an analytical solution and the state dependent part becomes a lineareigenvalue problem which can readily be solved using standard software.
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| 49. |
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| 50. |
- Rutquist, Per, 1976, et al.
(författare)
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Solving the Hamilton-Jacobi-Bellman Equation for a Stochastic System with State Constraints
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a method for solving the Hamilton-Jacobi-Bellman(HJB) equation for a stochastic system with state constraints. A variable transformation is introduced which turns the HJB equation into a combination of a linear eigenvalue problem, a set of partial differentialequations (PDE:s), and a point-wise equation. For a fixed solution to the eigenvalue problem, the PDE:s are linear and the point-wise equation is quadratic, indicating that the problem can be solved efficiently using an iterative scheme. As an example, we numerically solve for the optimal control of a Linear Quadratic Gaussian (LQG) system with state constraints. A reasonably accurate solution is obtained even with a very small number of collocation points (three in each dimension), which suggests that the method could be used on high order systems, mitigating the curse of dimensionality.
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