| 1. |
- Briat, Corentin, et al.
(author)
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Design of LPV observers for LPV time-delay systems : an algebraic approach
- 2011
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In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 84:9, s. 1533-1542
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Journal article (peer-reviewed)abstract
- The design of reduced order observer for linear parameter varying (LPV) time-delay systems is addressed. Necessary conditions guaranteeing critical structural properties for the observation error dynamics are first provided through nonlinear algebraic matrix equalities. An explicit parametrisation of the family of observers fulfilling these necessary conditions is then derived. Finally, an approach based on linear matrix inequalities is provided and used to select a suitable observer within this family, according to some criterion; e.g. maximisation of the delay margin or guaranteed suboptimal L(2)-gain. Examples from the literature illustrate the efficiency of the approach.
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| 2. |
- Cescon, Marzia, et al.
(author)
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Identification of Individualized Empirical Models of Carbohydrate and Insulin Effects on T1DM Blood Glucose Dynamics
- 2014
-
In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 87:7, s. 1438-1453
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Journal article (peer-reviewed)abstract
- One of the main limiting factors in improving glucose control for type 1 diabetes mellitus (T1DM) subjects is the lack of a precise description of meal and insulin intake effects on blood glucose. Knowing the magnitude and duration of such effects would be useful not only for patients and physicians, but also for the development of a controller targeting glycaemia regulation. Therefore, in this paper we focus on estimating low-complexity yet physiologically sound and individualised multi-input single-output (MISO) models of the glucose metabolism in T1DM able to reflect the basic dynamical features of the glucose-insulin metabolic system in response to a meal intake or an insulin injection. The models are continuous-time second-order transfer functions relating the amount of carbohydrate of a meal and the insulin units of the accordingly administered dose (inputs) to plasma glucose evolution (output) and consist of few parameters clinically relevant to be estimated. The estimation strategy is continuous-time data-driven system identification and exploits a database in which meals and insulin boluses are separated in time, allowing the unique identification of the model parameters.
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| 3. |
- Fabri, Simon G, et al.
(author)
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Dual adaptive extremum control of Hammerstein models
- 2015
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In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 88:6, s. 1271-1286
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Journal article (peer-reviewed)abstract
- A novel dual adaptive controller for extremum control of stochastic and uncertain nonlinear Hammerstein systems is proposed. The design is based on the innovations dual control cost function originally developed for conventional adaptive control of linear systems. However, the design process is extensively modified and developed so as to cater for the extremum control scenario. This is a more challenging problem because the reference input is itself a nonlinear function of the unknown system parameters, rather than an independent and predefined external reference signal. As in all dual adaptive schemes, it leads to a control law that balances out the need for caution, due to parameter uncertainty, with the conflicting requirement of probing that acts to quickly reduce parameter uncertainty. The proposed controller’s performance is analysed through extensive Monte Carlo simulation trials and compared with several other non-dual adaptive extremum controllers. It is shown that the novel extremum innovations dual controller is superior to other types of adaptive control systems that are based on a certainty equivalence assumption. In addition, a novel statistical measure is introduced that yields a more objective evaluation of the Monte Carlo simulation results.
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| 4. |
- Falkeborn, Rikard, et al.
(author)
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Low-Rank Exploitation in Semidefinite Programming for Control
- 2011
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In: International Journal of Control. - : Taylor & Francis. - 0020-7179 .- 1366-5820. ; 84:12, s. 1975-1982
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Journal article (peer-reviewed)abstract
- Many control-related problems can be cast as semidefinite programs. Even though there exist polynomial time algorithms and excellent publicly available solvers, the time it takes to solve these problems can be excessive. What many of these problems have in common, in particular in control, is that some of the variables enter as matrix-valued variables. This leads to a low-rank structure in the basis matrices which can be exploited when forming the Newton equations. In this article, we describe how this can be done, and show how our code, called STRUL, can be used in conjunction with the semidefinite programming solver SDPT3. The idea behind the structure exploitation is classical and is implemented in LMI Lab, but we show that when using a modern semidefinite programming framework such as SDPT3, the computational time can be significantly reduced. Finally, we describe how the modelling language YALMIP has been changed in such a way that our code, which can be freely downloaded, can be interfaced using standard YALMIP commands. This greatly simplifies modelling and usage.
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| 5. |
- Gros, Sébastien, 1977, et al.
(author)
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Real-time economic nonlinear model predictive control for wind turbine control
- 2017
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In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 90:12, s. 2799-2812
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Journal article (peer-reviewed)abstract
- Nonlinear model predictive control (NMPC) is a strong candidate to handle the control challenges emerging in the modern wind energy industry. Recent research suggested that wind turbine (WT) control based on economic NMPC (ENMPC) can improve the closed-loop performance and simplify the task of controller design when compared to a classical NMPC approach. This paper establishes a formal relationship between the ENMPC controller and the classic NMPC approach, and compares empirically their closed-loop nominal behaviour and performance. The robustness of the performance is assessed for an inaccurate modelling of the tower fore-aft main frequency. Additionally, though a perfect wind preview is assumed here, the effect of having a limited horizon of preview of the wind speed via the LIght Detection And Ranging (LIDAR) sensor is investigated. Finally, this paper provides new algorithmic solutions for deploying ENMPC for WT control, and report improved computational times.
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| 6. |
- Guo, Meng, 1988-, et al.
(author)
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Nonlinear consensus via continuous, sampled, and aperiodic updates
- 2013
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In: International Journal of Control. - : Taylor & Francis. - 0020-7179 .- 1366-5820. ; 86:4, s. 567-578
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Journal article (peer-reviewed)abstract
- We consider a first-order multi-agent system with nonlinear control protocols performing consensus. We first address the convergence properties of the continuous system. Then periodically sampled control inputs are treated, where we derive explicit upper bounds on the sampling interval to preserve global stability. Moreover, we design an aperiodic and event-triggered updating law to reduce the control efforts even further while ensuring the closed-loop stability and providing a strictly positive lower bound on the inter-execution time. Finally, the robustness of this approach with respect to additive disturbances is examined by applying L-2 gain analysis.
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| 7. |
- Gusev, Sergei V., et al.
(author)
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SDP-based approximation of stabilising solutions for periodic matrix Riccati differential equations
- 2016
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In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 89:7, s. 1396-1405
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Journal article (peer-reviewed)abstract
- Numerically finding stabilising feedback control laws for linear systems of periodic differential equations is a nontrivial task with no known reliable solutions. The most successful method requires solving matrix differential Riccati equations with periodic coefficients. All previously proposed techniques for solving such equations involve numerical integration of unstable differential equations and consequently fail whenever the period is too large or the coefficients vary too much. Here, a new method for numerical computation of stabilising solutions for matrix differential Riccati equations with periodic coefficients is proposed. Our approach does not involve numerical solution of any differential equations. The approximation for a stabilising solution is found in the form of a trigonometric polynomial, matrix coefficients of which are found solving a specially constructed finite-dimensional semidefinite programming (SDP) problem. This problem is obtained using maximality property of the stabilising solution of the Riccati equation for the associated Riccati inequality and sampling technique. Our previously published numerical comparisons with other methods shows that for a class of problems only this technique provides a working solution. Asymptotic convergence of the computed approximations to the stabilising solution is proved below under the assumption that certain combinations of the key parameters are sufficiently large. Although the rate of convergence is not analysed, it appeared to be exponential in our numerical studies.
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| 8. |
- Hansson, Anders, et al.
(author)
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Sampling method for semidefinite programmes with non-negative Popov function constraints
- 2014
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In: International Journal of Control. - : Taylor and Francis: STM, Behavioural Science and Public Health Titles. - 0020-7179 .- 1366-5820. ; 87:2, s. 330-345
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Journal article (peer-reviewed)abstract
- An important class of optimisation problems in control and signal processing involves the constraint that a Popov function is non-negative on the unit circle or the imaginary axis. Such a constraint is convex in the coefficients of the Popov function. It can be converted to a finite-dimensional linear matrix inequality via the Kalman-Yakubovich-Popov lemma. However, the linear matrix inequality reformulation requires an auxiliary matrix variable and often results in a very large semidefinite programming problem. Several recently published methods exploit problem structure in these semidefinite programmes to alleviate the computational cost associated with the large matrix variable. These algorithms are capable of solving much larger problems than general-purpose semidefinite programming packages. In this paper, we address the same problem by presenting an alternative to the linear matrix inequality formulation of the non-negative Popov function constraint. We sample the constraint to obtain an equivalent set of inequalities of low dimension, thus avoiding the large matrix variable in the linear matrix inequality formulation. Moreover, the resulting semidefinite programme has constraints with low-rank structure, which allows the problems to be solved efficiently by existing semidefinite programming packages. The sampling formulation is obtained by first expressing the Popov function inequality as a sum-of-squares condition imposed on a polynomial matrix and then converting the constraint into an equivalent finite set of interpolation constraints. A complexity analysis and numerical examples are provided to demonstrate the performance improvement over existing techniques.
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| 9. |
- Harju Johansson, Janne, et al.
(author)
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An Inexact Interior-Point Method for System Analysis
- 2010
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In: International Journal of Control. - : Taylor & Francis. - 0020-7179 .- 1366-5820. ; 83:3, s. 601-616
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Journal article (peer-reviewed)abstract
- In this article, a primal-dual interior-point algorithm for semidefinite programming that can be used for analysing e.g. polytopic linear differential inclusions is tailored in order to be more computationally efficient. The key to the speedup is to allow for inexact search directions in the interior-point algorithm. These are obtained by aborting an iterative solver for computing the search directions prior to convergence. A convergence proof for the algorithm is given. Two different preconditioners for the iterative solver arc proposed. The speedup is in many cases more than an order of magnitude. Moreover, the proposed algorithm can be used to analyse much larger problems as compared to what is possible with off-the-shelf interior-point solvers.
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| 10. |
- Kirchsteiger, Harald, et al.
(author)
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Continuous-Tme Interval Model Identification of Blood Glucose Dynamics for Type 1 Diabetes
- 2014
-
In: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 87:7, s. 1454-1466
-
Journal article (peer-reviewed)abstract
- While good physiological models of the glucose metabolism in type 1 diabetic patients are well known, their parameterisation is difficult. The high intra-patient variability observed is a further major obstacle. This holds for data-based models too, so that no good patient-specific models are available. Against this background, this paper proposes the use of interval models to cover the different metabolic conditions. The control-oriented models contain a carbohydrate and insulin sensitivity factor to be used for insulin bolus calculators directly. Available clinical measurements were sampled on an irregular schedule which prompts the use of continuous-time identification, also for the direct estimation of the clinically interpretable factors mentioned above. An identification method is derived and applied to real data from 28 diabetic patients. Model estimation was done on a clinical data-set, whereas validation results shown were done on an out-of-clinic, everyday life data-set. The results show that the interval model approach allows a much more regular estimation of the parameters and avoids physiologically incompatible parameter estimates.
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