| 291. |
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| 292. |
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| 293. |
- Mesbah, A., et al.
(författare)
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A unified experiment design framework for detection and identification in closed-loop performance diagnosis
- 2012
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Ingår i: Decision and Control (CDC), 2012 IEEE 51st Annual Conference on. - : IEEE. ; , s. 2152-2157
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Konferensbidrag (refereegranskat)abstract
- This paper presents a least-costly experiment design framework for closed-loop performance diagnosis using prediction error identification. The performance diagnosis methodology consists in verifying whether an identified model of the true system lies in a performance-related region of interest. The experiment design framework minimizes the overall excitation cost incurred for detecting the cause of the performance drop and re-identifying the system dynamics when the degraded performance is due to control-relevant system changes. The optimal design of excitation signals is performed for a desired detection rate and a pre-specified level of accuracy required for the re-identified model.
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| 294. |
- Mesbah, A., et al.
(författare)
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Least costly closed-loop performance diagnosis and plant re-identification
- 2015
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Ingår i: International Journal of Control. - : Taylor & Francis. - 0020-7179 .- 1366-5820. ; 88:11, s. 2264-2276
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Tidskriftsartikel (refereegranskat)abstract
- The inherent time-varying nature of dynamics in chemical processes often limits the lifetime performance of model-based control systems, as the plant and disturbance dynamics change over time. A critical step in the maintenance of model-based controllers is distinguishing control-relevant plant changes from variations in disturbance characteristics. In this paper, prediction error identification is used to evaluate a hypothesis test that detects if the performance drop arises from control-relevant plant changes. The decision rule is assessed by verifying whether an identified model of the true plant lies outside the set of all plant models that lead to adequate closed-loop performance. A unified experiment design framework is presented in the least costly context (i.e., least intrusion of nominal plant operation) to address the problem of input signal design for performance diagnosis and plant re-identification when the performance drop is due to plant changes. The application of the presented performance diagnosis approach to a (nonlinear) chemical reactor demonstrates the effectiveness of the approach in detecting the cause of an observed closed-loop performance drop based on the designed least costly diagnosis experiment.
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| 295. |
- Moghadam, Nima N., 1986-, et al.
(författare)
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Correlation of distortion noise between the branches of MIMO transmit antennas
- 2012
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on. - : IEEE. - 9781467325691 ; , s. 2079-2084
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Konferensbidrag (refereegranskat)abstract
- Despite the tremendous research effort spent on MIMO systems - very few papers address the impact of hardware imperfections. In this paper we analyze the distortion noise of the transmitter branches of a MIMO transmitter. In particular we analyze the cross-correlation of the distortion noises for the case that the transmitted signals are correlated. This case arises when there is just a single stream being transmitted with beamforming or in the case of multiple streams and linear precoding. We analyze the problem in two ways: using analytical derivations and using measurements on our testbed. In the analytical case we assume a transmitter impaired by a 3rd order non-linearity. For this scenario we find that the absolute correlation coefficient of the distortion noises is given by the absolute value of the correlation coefficients of the input signals to the power of three, while the phase is the same as that of the input signal. Our measurements also show good agreement between measurements and analytical results. It seems to suggest that the distortion noises can be regarded as practically independent whenever there are two or more modulation streams being transmitted (spatial multiplexing). In a single-stream scenario, the distortion noise will tend to have the same spatial distribution as the desired signal.
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| 296. |
- Morelli, Federico, et al.
(författare)
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Least costly identification experiment for the identification of one module in a dynamic network
- 2021
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 133
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the design of least costly experiments for the identification of one module in a given network of locally controlled systems. The identification experiment will be designed in such a way that we obtain a sufficiently accurate model of the to-be-identified module with the smallest identification cost i.e. with the least perturbation of the network.
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| 297. |
- Morelli, F., et al.
(författare)
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Optimal Experiment Design for the Identification of One Module in the Interconnection of Locally Controlled Systems
- 2019
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Ingår i: 2019 18TH EUROPEAN CONTROL CONFERENCE (ECC). - : IEEE. ; , s. 363-368
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider the problem of designing the least costly experiment that leads to a sufficiently accurate estimate of one module in a network of locally controlled systems. A module in such a network can be identified by exciting the corresponding local closed loop system. Such an excitation signal will not only perturb the input/output of the to-be-identified module, but also other modules due to the interconnection. Consequently, the cost of the identification can be expressed as the sum of the influence of the excitation signal on the inputs and outputs of all locally controlled systems. We develop a methodology to design the spectrum of the excitation signal in such a way that this cost is minimized while guaranteeing a certain accuracy for the identified model. We also propose an alternative identification configuration which can further reduce the propagation of the excitation signal to other modules and we make steps to robustify this optimal experiment design problem with respect to the cost of the identification.
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| 298. |
- Müller, Matias I.
(författare)
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Learning Sequential Decision Rules in Control Design: Regret-Optimal and Risk-Coherent Methods
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Engineering sciences deal with the problem of optimal design in the face of uncertainty. In particular, control engineering is concerned about designing policies/laws/algorithms that sequentially take decisions given unreliable data. This thesis addresses two particular instances of optimal sequential decision making for two different problems.The first problem is known as the H∞-norm (or, in general, ℓ2-gain for nonlinear systems) estimation problem, which is a fundamental quantity in control design through, e.g., the small gain theorem. Given an unknown system, the goal is to find the maximum ℓ2-gain which, in a model-free approach, involves solving a sequential input design problem. The H∞-norm estimation problem (or simply "gain estimation problem") is cast as the composition of multi-armed bandit problem generating data, and an optimal estimation problem given that data. The problem of generating data is a sequential input-design problem in which, at every round, the decision-maker chooses one (or many) frequencies to sample from the unknown frequency response of the system under study. We show that Thompson Sampling (TS), a classical bandit algorithm, is optimal within the class of algorithms that chooses only one frequency per round. Additionally, we introduce Weighted Thompson Sampling (WTS), which is a TS-based algorithm that can sample many frequencies at every round. In this thesis, we prove that WTS is an optimal bandit policy within the class of algorithms that can sample many frequencies simultaneously. On the other hand, the problem of estimating the H∞-norm of the system using the data provided by the bandit algorithm is also discussed. In particular, we show that the expected estimation error of the gain of the system asymptotically matches the Cramér-Rao lower bound for a proposed estimator, and for every bandit policy in a wide class of algorithms.In the second part, we address the problem of risk-coherent optimal control design for disturbance rejection under uncertainty, where optimality is studied from an H2 and an H∞ sense. We consider a parametric model for the plant and the noise spectrum, where the modeling error between the model and the real system is uncertain. This uncertainty is condensed in a probability density function over the different realizations of the parameters defining the model. We use this information to design a controller that minimizes the risk of falling into poor closed-loop performance within a financial theory of risk framework. When the parameters in the plant are not known with sufficient accuracy for control purposes, we introduce a framework that allows us to tackle the joint-stabilization problem by means of sequential convex relaxations, each of them leading to a semi-definite program. On the other hand, when the noise spectrum is uncertain, we propose a systematic scenario approach for designing H2- and H∞-optimal controllers in terms of quadratically-constrained linear programs and sequential semi-definite programming, respectively. Simulations show that, from a risk-theoretical perspective, exploiting the information encoded in the probability density function of the parameters defining the models better balances the risk of falling into poor closed-loop performances.
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| 299. |
- Mårtensson, Jonas, et al.
(författare)
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A geometric approach to variance analysis in system identification : Linear Time-Invariant Systems
- 2007
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Ingår i: PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL. ; , s. 4269-4274
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Konferensbidrag (refereegranskat)abstract
- This paper addresses the problem of quantifying the model error ("variance-error") in estimates of linear time invariant systems. Building on the results in H. Hjalmarsson and J. Martensson (2007), we present an explicit method to construct an expression for the asymptotic variance of system properties such as impulse response coefficients, system gain, or the performance of some (control) application where the identified model is used. The expression is such that the individual impacts of model structure, model order and experimental conditions become visible. The technique is used to derive asymptotic variance expressions for a number of system properties.
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| 300. |
- Mårtensson, Jonas, et al.
(författare)
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Closed loop identification of unstable poles and non-minimum phase zeros
- 2005
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - Prague : Elsevier BV. - 9780080451084 ; , s. 518-523
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Konferensbidrag (refereegranskat)abstract
- This paper addresses estimation of poles and zeros in closed loop systems. For many quantities of interest, e.g. frequency function estimates, overparameterization results in a large increase of the variance but this is not the case for estimates of nonminimum phase zeros and unstable poles. Variance expressions that are asymptotic in model order and sample size are derived and for some systems it is found that open loop and closed loop experiments give the same accuracy.
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