| 1. |
- Solyom, Stefan, et al.
(författare)
-
ABS control - A design model and control structure
- 2003
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Ingår i: Nonlinear and Hybrid Systems in Automotive Control. ; , s. 85-96
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Anti-lock Braking System is an important component of acomplex steering system for the modern car. Most of ABS controllersavailable on the market are table and relay-feedback based.In the latest generation of “brake by wire” systems, the performancerequirements on the ABS are much higher. Control objective shiftsto maintain a specified tire slip during braking. The authors propose a design model and based on that a gain-scheduled controller that regulates the tire-slip. Simulation and test results are presented.
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| 2. |
- Andersen, Martin, et al.
(författare)
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Distributed Robust Stability Analysis of Interconnected Uncertain Systems
- 2012
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Ingår i: Proceedings of the 51st IEEE Conference on Decision and Control. - 0743-1546. - 9781467320641 - 9781467320658 ; , s. 1548-1553
-
Konferensbidrag (refereegranskat)abstract
- This paper considers robust stability analysis of a large network of interconnected uncertain systems. To avoid analyzing the entire network as a single large, lumped system, we model the network interconnections with integral quadratic constraints. This approach yields a sparse linear matrix inequality which can be decomposed into a set of smaller, coupled linear matrix inequalities. This allows us to solve the analysis problem efficiently and in a distributed manner. We also show that the decomposed problem is equivalent to the original robustness analysis problem, and hence our method does not introduce additional conservativeness.
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| 3. |
- Andersen, Martin S., et al.
(författare)
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Robust Stability Analysis of Sparsely Interconnected Uncertain Systems
- 2014
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Ingår i: IEEE Transactions on Automatic Control. - : IEEE. - 0018-9286 .- 1558-2523. ; 59:8, s. 2151-2156
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider robust stability analysis of large-scale sparsely interconnected uncertain systems. By modeling the interconnections among the subsystems with integral quadratic constraints, we show that robust stability analysis of such systems can be performed by solving a set of sparse linear matrix inequalities. We also show that a sparse formulation of the analysis problem is equivalent to the classical formulation of the robustness analysis problem and hence does not introduce any additional conservativeness. The sparse formulation of the analysis problem allows us to apply methods that rely on efficient sparse factorization techniques, and our numerical results illustrate the effectiveness of this approach compared to methods that are based on the standard formulation of the analysis problem.
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| 4. |
- Axehill, Daniel, 1978-
(författare)
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Applications of Integer Quadratic Programming in Control and Communication
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main topic of this thesis is integer quadratic programming with applications to problems arising in the areas of automatic control and communication. One of the most widespread modern control principles is the discrete-time method Model Predictive Control (MPC). The main advantage with MPC, compared to most other control principles, is that constraints on control signals and states can easily be handled. In each time step, MPC requires the solution of a Quadratic Programming (QP) problem. To be able to use MPC for large systems, and at high sampling rates, optimization routines tailored for MPC are used. In recent years, the range of application of MPC has been extended from constrained linear systems to so-called hybrid systems. Hybrid systems are systems where continuous dynamics interact with logic. When this extension is made, binary variables are introduced in the problem. As a consequence, the QP problem has to be replaced by a far more challenging Mixed Integer Quadratic Programming (MIQP) problem. Generally, for this type of optimization problems, the computational complexity is exponential in the number of binary optimization variables. In modern communication systems, multiple users share a so-called multi-access channel, where the information sent by different users is separated by using almost orthogonal codes. Since the codes are not completely orthogonal, the decoded information at the receiver is slightly correlated between different users. Further, noise is added during the transmission. To estimate the information originally sent, a maximum likelihood problem involving binary variables is solved. The process of simultaneously estimating the information sent by multiple users is called multiuser detection. In this thesis, the problem to efficiently solve MIQP problems originating from MPC is addressed. Two different algorithms are presented. First, a polynomial complexity preprocessing algorithm for binary quadratic programming problems is presented. By using the algorithm, some, or all, binary variables can be computed efficiently already in the preprocessing phase. In simulations, the algorithm is applied to unconstrained MPC problems with a mixture of real and binary control signals. It has also been applied to the multiuser detection problem, where simulations have shown that the bit error rate can be significantly reduced by using the proposed algorithm as compared to using common suboptimal algorithms. Second, an MIQP algorithm tailored for MPC is presented. The algorithm uses a branch and bound method where the relaxed node problems are solved by a dual active set QP algorithm. In this QP algorithm, the KKT-systems are solved using Riccati recursions in order to decrease the computational complexity. Simulation results show that both the QP solver and the MIQP solver proposed have lower computational complexity than corresponding generic solvers.
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| 5. |
- Cederberg, Daniel, et al.
(författare)
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Synthesis of Minimax Adaptive Controller for a Finite Set of Linear Systems
- 2022
-
Ingår i: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : IEEE. - 2576-2370 .- 0743-1546. - 9781665467612 - 9781665467629 ; , s. 1380-1384
-
Konferensbidrag (refereegranskat)abstract
- The design of an adaptive controller with bounded L-2-gain from disturbances to errors for linear time-invariant systems with uncertain parameters restricted to a finite set is investigated. The synthesis of the controller requires finding matrices satisfying non-convex matrix inequalities. We propose an approach for finding these matrices based on repeatedly linearizing the terms that cause the non-convexity of the inequalities. Empirical evidence suggests that the approach leads to adaptive controllers with significantly smaller upper bound on the L-2-gain.
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| 6. |
- Khoshfetrat Pakazad, Sina, 1985-, et al.
(författare)
-
Decomposition and Projection Methods for Distributed Robustness Analysis of Interconnected Uncertain Systems
- 2013
-
Konferensbidrag (refereegranskat)abstract
- We consider a class of convex feasibility problems where the constraints that describe the feasible set are loosely coupled. These problems arise in robust stability analysis of large, weakly interconnected uncertain systems. To facilitate distributed implementation of robust stability analysis of such systems, we describe two algorithms based on decomposition and simultaneous projections. The first algorithm is a nonlinear variant of Cimmino's mean projection algorithm, but by taking the structure of the constraints into account, we can obtain a faster rate of convergence. The second algorithm is devised by applying the alternating direction method of multipliers to a convex minimization reformulation of the convex feasibility problem. We use numerical results to show that both algorithms require far less iterations than the accelerated nonlinear Cimmino algorithm.
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| 7. |
- Khoshfetrat Pakazad, Sina, et al.
(författare)
-
Decomposition and Projection Methods for Distributed Robustness Analysis of Interconnected Uncertain Systems
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider a class of convex feasibility problems where the constraints that describe the feasible set are loosely coupled. These problems arise in robust stability analysis of large, weakly interconnected systems. To facilitate distributed implementation of robust stability analysis of such systems, we propose two algorithms based on decomposition and simultaneous projections. The first algorithm is a nonlinear variant of Cimmino’s mean projection algorithm, but by taking the structure of the constraints into account, we can obtain a faster rate of convergence. The second algorithm is devised by applying the alternating direction method of multipliers to a convex minimization reformulation of the convex feasibility problem. We use numerical results to show that both algorithms require far less iterations than the accelerated nonlinear Cimmino algorithm.
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| 8. |
- Khoshfetrat Pakazad, Sina, et al.
(författare)
-
Decomposition and Simultaneous Projection Methods for Convex Feasibility Problems with Application to robustness Analysis of Interconnected Uncertain Systems
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a specific class of convex feasibility problems are considered and tailored algorithms to solve this class of problems are introduced. First, the Nonlinear Cimmino Algorithm is reviewed. Then motivated by the special structure of the problems at hand, a modification to this method is proposed. Next, another method for solving the dual problem of the provided problem is presented. This leads to similar update rules for the variables as in the modified Nonlinear Cimmino Algorithm. Then an application for the proposed algorithms on the robust stability analysis of large scale weakly interconnected systems is presented and the performance of the proposed methods are compared.
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| 9. |
- Khoshfetrat Pakazad, Sina, 1985-, et al.
(författare)
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Distributed Robustness Analysis of Interconnected Uncertain Systems Using Chordal Decomposition
- 2014
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Ingår i: Proceedings of the 19th IFAC World Congress, 2014. - : International Federation of Automatic Control. - 9783902823625 ; , s. 2594-2599
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Konferensbidrag (refereegranskat)abstract
- Large-scale interconnected uncertain systems commonly have large state and uncertainty dimensions. Aside from the heavy computational cost of solving centralized robust stability analysis techniques, privacy requirements in the network can also introduce further issues. In this paper, we utilize IQC analysis for analyzing large-scale interconnected uncertain systems and we evade these issues by describing a decomposition scheme that is based on the interconnection structure of the system. This scheme is based on the so-called chordal decomposition and does not add any conservativeness to the analysis approach. The decomposed problem can be solved using distributed computational algorithms without the need for a centralized computational unit. We further discuss the merits of the proposed analysis approach using a numerical experiment.
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| 10. |
- Khoshfetrat Pakazad, Sina, 1985-, et al.
(författare)
-
Distributed Semidefinite Programming with Application to Large-scale System Analysis
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Distributed algorithms for solving coupled semidefinite programs (SDPs) commonly require manyiterations to converge. They also put high computational demand on the computational agents. In thispaper we show that in case the coupled problem has an inherent tree structure, it is possible to devisean efficient distributed algorithm for solving such problems. This algorithm can potentially enjoy thesame efficiency as centralized solvers that exploit sparsity. The proposed algorithm relies on predictorcorrectorprimal-dual interior-point methods, where we use a message-passing algorithm to compute thesearch directions distributedly. Message-passing here is closely related to dynamic programming overtrees. This allows us to compute the exact search directions in a finite number of steps. Furthermorethis number can be computed a priori and only depends on the coupling structure of the problem. Weuse the proposed algorithm for analyzing robustness of large-scale uncertain systems distributedly. Wetest the performance of this algorithm using numerical examples.
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| 11. |
- Khoshfetrat Pakazad, Sina, et al.
(författare)
-
Distributed Semidefinite Programming with Application to Large-scale System Analysis
- 2018
-
Ingår i: IEEE Transactions on Automatic Control. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9286 .- 1558-2523. ; 63:4
-
Tidskriftsartikel (refereegranskat)abstract
- Distributed algorithms for solving coupled semidefinite programs (SDPs) commonly require many iterations to converge. They also put high computational demand on the computational agents. In this paper we show that in case the coupled problem has an inherent tree structure, it is possible to devise an efficient distributed algorithm for solving such problems. The proposed algorithm relies on predictor-corrector primal-dual interior-point methods, where we use a message-passing algorithm to compute the search directions distributedly. Message-passing here is closely related to dynamic programming over trees. This allows us to compute the exact search directions in a finite number of steps. This is because, computing the search directions requires a recursion over the tree structure and hence, terminates after an upward and downward pass through the tree. Furthermore this number can be computed apriori and only depends on the coupling structure of the problem. We use the proposed algorithm for analyzing robustness of large-scale uncertain systems distributedly. We test the performance of this algorithm using numerical examples.
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| 12. |
- Sun, Zhiyong, et al.
(författare)
-
Distributed adaptive stabilization
- 2021
-
Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 129
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider distributed adaptive stabilization for uncertain multivariable linear systems with a time-varying diagonal matrix gain. We show that uncertain multivariable linear systems are stabilizable by diagonal matrix high gains if the system matrix is an H-matrix with positive diagonal entries. Based on matrix measure and stability theory for diagonally dominant systems, we consider two classes of uncertain linear systems, and derive a threshold condition to ensure their exponential stability by a monotonically increasing diagonal gain matrix. When each individual gain function in the matrix gain is updated by state-dependent functions using only local state information, the boundedness and convergence of both system states and adaptive matrix gains are guaranteed. We apply the adaptive distributed stabilization approach to adaptive synchronization control for large-scale complex networks consisting of nonlinear node dynamics and time-varying coupling weights. A unified framework for adaptive synchronization is proposed that includes several general design approaches for adaptive coupling weights to guarantee network synchronization.
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| 13. |
- Sun, Zhiyong, et al.
(författare)
-
On distributed high-gain adaptive stabilization
- 2019
-
Ingår i: 2019 IEEE 58th Conference on Decision and Control, CDC 2019. - 2576-2370 .- 0743-1546. - 9781728113999 - 9781728113982 ; 2019-December, s. 1083-1088
-
Konferensbidrag (refereegranskat)abstract
- In this paper we consider adaptive distributed stabilization for uncertain multivariable linear systems with a time-varying diagonal matrix gain. We show that an unknown system matrix being an M-matrix is a sufficient condition to ensure uncertain linear systems to be stabilizable by matrix high gains, and derive a threshold condition to ensure exponential stability of uncertain linear systems stabilized by a monotonically increasing diagonal gain matrix. When each individual gain function in the matrix gain is updated by state-dependent functions, the boundedness and convergence of both system states and adaptive matrix gains are guaranteed. We apply the matrix gain stabilization approach to adaptive synchronization control for complex networks with time-varying coupling weights.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Agner, Felix, et al.
(författare)
-
Anti-windup coordination strategy around a fair equilibrium in resource sharing networks
- 2023
-
Ingår i: IEEE Control Systems Letters. - 2475-1456.
-
Tidskriftsartikel (refereegranskat)abstract
- We coordinate interconnected agents where the control input of eachagent is limited by the control input of others. In that sense, the sys-tems have to share a limited resource over a network. Such problems canarise in different areas and it is here motivated by a district heating ex-ample. When the shared resource is insufficient for the combined needof all systems, the resource will have to be shared in an optimal fash-ion. In this scenario, we want the systems to automatically converge toan optimal equilibrium. The contribution of this paper is the proposalof a control architecture where each separate system is controlled by alocal PI controller. The controllers are then coordinated through a globalrank-one anti-windup signal. It is shown that the equilibrium of the pro-posed closed-loop system minimizes the infinity-norm of stationary statedeviations. A proof of linear-domain passivity is given, and a numericalexample highlights the benefits of the proposed method with respect tothe state-of-the-art.
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| 18. |
- Agner, Felix, et al.
(författare)
-
Combating district heating bottlenecks using load control
- 2022
-
Ingår i: Smart Energy. - : Elsevier BV. - 2666-9552. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The 4th generation of district heating systems face a potential problem where lowered water temperatures lead to higher flow rates, which requires higher hydraulic capacity in terms of pipe and pump sizes. This increases the effect of the already existing issue of hydraulic bottlenecks, causing peripheral units (customers) to experience reduced flow rates. A coordinating control strategy is presented in this work aimed at reducing the effect of such bottlenecks on the comfort of customers. This is done by distributing the flow deficit over many units rather than a few. Previous works mainly focus on MPC-structured controllers that depend on complex system models and online optimization techniques. This work proposes a method that requires little information about models for individual units and minimal IT communication between control systems. The proposed method is compared with a traditional control strategy and an optimal baseline in a simulation study. This shows that the proposed method can decrease the worst case indoor temperature deviations.
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| 19. |
- Agner, Felix, et al.
(författare)
-
Decentralized PI-control and Anti-windup in Resource Sharing Networks
- 2024
-
Ingår i: European Journal of Control. - 1435-5671.
-
Tidskriftsartikel (refereegranskat)abstract
- We consider control of multiple stable first-order systems which have a control coupling described by an M-matrix. These agents are subject to incremental sector-bounded nonlinearities. We show that such plants can be globally asymptotically stabilized to a unique equilibrium using fully decentralized proportional integral anti-windup-equipped controllers subject to local tuning rules. In addition, we show that when the nonlinearities correspond to the saturation function, the closed-loop asymptotically minimizes a weighted 1-norm of the agents state mismatch. The control strategy is finally compared to other state-of-the-art controllers on a numerical district heating example.
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| 20. |
|
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| 21. |
- Agner, Felix, et al.
(författare)
-
Fair heat distribution under deficits in district heating networks
- 2021
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In order to improve the energy efficiency in district heating networks and the comfort of their customers, these networks need to overcome the problem of unfair heat distribution under heat deficits. This paper introduces a new strategy to achieve this thermal fairness objective: it is lowcost in terms of communication and computation. The proposed approach is illustrated on a simulation example.
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| 22. |
- Agner, Felix, et al.
(författare)
-
Hydraulic Parameter Estimation in District Heating Networks
- 2023
-
Ingår i: IFAC PaperOnLine. - 9781713872344 ; 56, s. 5438-5443
-
Konferensbidrag (refereegranskat)abstract
- Using hydraulic models in control design in district heating networks can increase pumping efficiency and reduce sensitivity to hydraulic bottlenecks. These models are usually white-box, as they are obtained based on full knowledge of the district heating network and its parameters. This type of model is time-consuming to obtain, and might differ from the actual behavior of the system. In this paper, a method is proposed to obtain a grey-box hydraulic model for tree-shaped district heating systems: hydraulic parameters are estimated based on pressure measurements in only two locations. While previous works only estimate parameters related to pressure losses in pipes, this work also includes customers valves in the grey-box model structure, an important inclusion for control-oriented applications. Finally, a numerical example illustrates the proposed method on a small district heating network, showing its ability to obtain an accurate model on the basis of noisy measurements.
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| 23. |
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| 24. |
- Almér, Stefan, et al.
(författare)
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Hybrid control techniques for switched-mode DC-DC converters part I : The step-down topology
- 2007
-
Ingår i: 2007 American Control Conference. - : IEEE. - 1424409888 - 9781424409884 ; , s. 5450-5457
-
Konferensbidrag (refereegranskat)abstract
- Several recent techniques from hybrid and optimal control are evaluated on a power electronics benchmark problem. The benchmark involves a number of practically interesting operating scenarios for a fixed-frequency synchronous step-down dc-dc converter. The specifications are defined such that good performance only can be obtained if the switched and nonlinear nature of the problem is respected during the design phase.
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| 25. |
- Alriksson, Peter, et al.
(författare)
-
Distributed Kalman Filtering Using Weighted Averaging
- 2006
-
Konferensbidrag (refereegranskat)abstract
- This paper addresses the problem of distributed Kalman filtering, with focus on limiting the required communication bandwidth. By distributed we refer to a scenario when all nodes in the network desire an estimate of the full state of the observed system and there is no centralized computation center. Communication only takes place between neighbors and only a fixed number of times each sample. To reduce bandwidth requirements of individual nodes, estimates instead of measurements are communicated. A new estimate is then formed as a weighted average of the neighbouring estimates. The weights are optimized to yield a small estimation error covariance in stationarity. The minimization can be done off line thus allowing only estimates to be communicated. The advantage of communicating estimates instead of measurements becomes more evident when the number of nodes exceeds the size of the state vector to be estimated. The algorithm is applied to one simple second order system and temperature sensing network.
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| 26. |
- Alriksson, Peter, et al.
(författare)
-
Experimental Evaluation of a Distributed Kalman Filter Algorithm
- 2007
-
Ingår i: ; , s. 3562-3567
-
Konferensbidrag (refereegranskat)abstract
- This paper evaluates the performance of a distributed Kalman filter applied to an ultrasound based positioning application with seven sensor nodes. By distributed we mean that all nodes in the network desires an estimate of the full state of the observed system and there is no centralized computation center after deployment. Communication only takes place between neighbors and only once each sampling interval. The problem is solved by communicating estimates between neighbors and then forming a weighted average as the new estimate. The weights are optimized to yield a small estimation error covariance in stationarity. The minimization can be done off line thus allowing only estimates to be communicated. In the experimental setup the distributed solution performs almost as good as a centralized solution. The proposed algorithm also proved very robust against packet loss.
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| 27. |
- Alriksson, Peter, et al.
(författare)
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Model Based Information Fusion in Sensor Networks
- 2008
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a model based sensor fusion algorithm for sensor networks is presented. The algorithm, referred to as distributed Kalman filtering is based on a previously presented algorithm with the same name. The weight selection process has been improved yielding performance improvements of several times for the examples studied. Also, solutions to both optimization problems involved in the iterative off-line weight selection process are given as closed form expressions. The algorithm is also demonstrated on a typical signal tracking application.
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| 28. |
- Alriksson, Peter, et al.
(författare)
-
Observer Synthesis for Switched Discrete-Time Linear Systems using Relaxed Dynamic Programming
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper, state estimation for Switched Discrete-Time Linear Systems is performed using relaxed dynamic programming. Taking the Bayesian point of view, the estimation problem is transformed into an infinite dimension al optimization problem. The optimization problem is then solved using relaxed dynamic programming. The estimate of both the mode and the continuous state can then be computed from the value-function. From an unknown initial state the estimation error goes to zero as more measurements are collected.
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| 29. |
- Alriksson, Peter, et al.
(författare)
-
Sub-Optimal Sensor Scheduling with Error Bounds
- 2005
-
Ingår i: Proceedings of the 16th IFAC World Congress. - 008045108X
-
Konferensbidrag (refereegranskat)abstract
- In this paper the problem of sub-optimal sensor schedulingwith a guaranteed distance to optimality is considered. Optimal in thesense that the sequence that minimizes the estimation error covariancematrix for a given time horizon is found. The search is done usingrelaxed dynamic programming. The algorithm is then applied to onesimple second order system and one sixth order model of a fixedmounted model lab helicopter.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Beccuti, A. G., et al.
(författare)
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Hybrid control techniques for switched-mode DC-DC converters part II : The step-up topology
- 2007
-
Ingår i: 2007 American Control Conference, Vols 1-13. - 1424409888 - 9781424409884 ; , s. 5464-5471
-
Konferensbidrag (refereegranskat)abstract
- Several recent techniques from hybrid and optimal control are evaluated on a power electronics benchmark problem. The benchmark involves a number of practically interesting operating scenarios for a fixed-frequency step-up dc-dc converter. The specifications are defined such that good performance can only be obtained if the switched and nonlinear nature of the problem is respected during the design phase.
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| 34. |
- Bencherki, Fethi, et al.
(författare)
-
Robust Simultaneous Stabilization Via Minimax Adaptive Control
- 2023
-
Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 9798350301243 ; , s. 2503-2508
-
Konferensbidrag (refereegranskat)abstract
- The paper explores the usage of minimax adaptive controllers to guarantee finite L2 -gain simultaneous stabilization of linear time-invariant (LTI) plants. It is shown that a minimax adaptive controller simultaneously stabilizes any two multiple-input multiple-output (MIMO) P-stabilizable LTI plants when no LTI controller can achieve that, and the worst attained L2 -gain bound for the transient dynamics is readily computable.
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| 35. |
- Bengtsson, Johan, et al.
(författare)
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Modeling of Driver's Longitudinal Behavior
- 2003
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Ingår i: Nonlinear and Hybrid Systems in Automotive Control. - 076801137X ; , s. 41-58
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In the last years, many vehicle manufacturers have introduced advancedriver support in some of their automobiles. One of those new featuresis Adaptive Cruise Control (ACC), which extends the conventionalcruise control system to control of relative speed and distance toother vehicles. In order to design an ACC controller it is suitable tohave a model on drivers' behavior. Our approach to find dynamicalmodels of the drivers' behavior was to use system identification.Basic data analysis was made by means of system identificationmethodology, and several models of drivers' longitudinal behavior areproposed, including both linear regression models and subspace basedmodels. Detection when a driver is changing his behavior in varioussituations to a deviant behavior is useful. To that purpose a GARCHmodel was used to model the driver in arousal situations, where thedriver changes behavior, is proposed.
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| 36. |
- Bergeling, Carolina, et al.
(författare)
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Closed-form H-infinity optimal control for a class of infinite-dimensional systems
- 2020
-
Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 117
-
Tidskriftsartikel (refereegranskat)abstract
- H-infinity optimal control and estimation are addressed for a class of systems governed by partial differential equations with bounded input and output operators. Diffusion equations are an important example in this class. Explicit formulas for the optimal state feedback controller as well as the optimal state estimator are given. Unlike traditional methods for H-infinity synthesis, no iteration is needed to obtain the optimal solution. Moreover, the optimal performance for both the state feedback and state estimation problems are explicitly calculated. This is shown to be useful for problems of H-infinity optimal actuator and sensor location. Furthermore, the results can be used in testing and bench-marking of general purpose algorithms for H-infinity synthesis. The results also apply to finite-dimensional systems.
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| 37. |
- Bergeling, Carolina, et al.
(författare)
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H-infinity Optimal Control for Systems with a Bottleneck Frequency
- 2021
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286. ; 66:6, s. 2732-2738
-
Tidskriftsartikel (refereegranskat)abstract
- We characterize a class of systems for which the H-infinity optimal control problem can be simplified in a way that enables sparse solutions and efficient computation. For a subclass of the systems, an optimal controller can be explicitly expressed in terms of the matrices of the system's state-space representation. In many applications, the controller given by this formula, which is static, can be implemented in a decentralized or distributed fashion. Examples are temperature dynamics in buildings, water irrigation and electrical networks.
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| 38. |
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| 39. |
- Biegel, Benjamin, et al.
(författare)
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Distributed Low-Complexity Controller for Wind Power Plant in Derated Operation
- 2013
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Konferensbidrag (refereegranskat)abstract
- We consider a wind power plant of megawatt wind turbines operating in derated mode. When operating in this mode, the wind power plant controller is free to distribute power set-points to the individual turbines, as long as the total power demand is met. In this work, we design a controller that exploits this freedom to reduce the fatigue on the turbines in the wind power plant. We show that the controller can be designed in a decentralized manner, such that each wind turbine is equipped with a local low-complexity controller relying only on few measurements and little communication. As a basis for the controller design, a linear wind turbine model is constructed and verified in an operational wind power plant of megawatt turbines. Due to limitations of the wind power plant available for tests, it is not possible to implement the developed controller; instead the final distributed controller is evaluated via simulations using an industrial wind turbine model. The simulations consistently show fatigue reductions in the magnitude of 15 – 20 %.
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| 40. |
- Chasparis, Georgios, et al.
(författare)
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A Decomposition Approach to Multi-Region Optimal Power Flow in Electricity Networks
- 2013
-
Ingår i: [Host publication title missing]. ; , s. 3024-3030
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a decomposition approach to a class of social welfare optimization problems for optimal power flow in multi-region electricity networks. The electricity network is decomposed into multiple regions which decide independently over the amount of power produced within the region and exchanged with neighboring regions. We decompose the overall power flow (or social welfare) optimization into region-based optimization problems (namely, power flow game), which is based on the introduction of dual variables representing nodal and link prices. Due to the interdependencies between regions’ utilities, the social welfare maximizer might not necessarily correspond to a Nash equilibrium of the power flow game. We derive conditions under which the social welfare maximizer is a Nash equilibrium of the game, and investigate uniqueness of Nash equilibria. Finally, we examine whether convergence to the social welfare maximizer may occur under natural best- response dynamics.
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| 41. |
- Chasparis, Georgios C., et al.
(författare)
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Nonconvergence to saddle boundary points under perturbed reinforcement learning
- 2015
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Ingår i: International Journal of Game Theory. - : Springer Science and Business Media LLC. - 1432-1270 .- 0020-7276. ; 44:3, s. 667-699
-
Tidskriftsartikel (refereegranskat)abstract
- For several reinforcement learning models in strategic-form games, convergence to action profiles that are not Nash equilibria may occur with positive probability under certain conditions on the payoff function. In this paper, we explore how an alternative reinforcement learning model, where the strategy of each agent is perturbed by a strategy-dependent perturbation (or mutations) function, may exclude convergence to non-Nash pure strategy profiles. This approach extends prior analysis on reinforcement learning in games that addresses the issue of convergence to saddle boundary points. It further provides a framework under which the effect of mutations can be analyzed in the context of reinforcement learning.
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| 42. |
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| 43. |
- Chasparis, Georgios, et al.
(författare)
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Perturbed Learning Automata in Potential Games
- 2011
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Konferensbidrag (refereegranskat)abstract
- This paper presents a reinforcement learning algorithm and provides conditions for global convergence to Nash equilibria. For several reinforcement learning schemes, including the ones proposed here, excluding convergence to action profiles which are not Nash equilibria may not be trivial, unless the step-size sequence is appropriately tailored to the specifics of the game. In this paper, we sidestep these issues by introducing a new class of reinforcement learning schemes where the strategy of each agent is perturbed by a state-dependent perturbation function. Contrary to prior work on equilibrium selection in games, where perturbation functions are globally state dependent, the perturbation function here is assumed to be local, i.e., it only depends on the strategy of each agent. We provide conditions under which the strategies of the agents will converge to an arbitrarily small neighborhood of the set of Nash equilibria almost surely. We further specialize the results to a class of potential games.
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| 44. |
- Chong, Michelle, et al.
(författare)
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Estimating the Wigner distribution of linear time-invariant dynamical systems
- 2018
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Ingår i: 2018 European Control Conference, ECC 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783952426982 ; , s. 1220-1225
-
Konferensbidrag (refereegranskat)abstract
- An estimation algorithm for the Wigner distribution (time-frequency representation) of the unmeasured states of a linear time-invariant system is presented. Given that the inputs and outputs are measured, the algorithm involves designing a Luenberger-like observer for each frequency of interest. Under noise-free conditions, we show that the es- timates converge to the true Wigner distribution under a detectability assumption on the time-frequency representation. The estimation algorithm provides estimates which converge to a neighbourhood of the true Wigner distribution where its norm is dependent on the norm of the measurement noise. We also illustrate the efficacy of the estimation algorithm on an academic example and a model of neuron populations.
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| 45. |
- Coimbatore Anand, Sribalaji, 1994-
(författare)
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Risk-Based Analysis and Design of Secure Control Systems
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Networked Control Systems (NCSs) are integral to many critical infrastructures such as power grids, transportation, and production systems. The resilient operation of such NCS against cyber-attacks is essential for society, and risk management presents an effective framework for addressing these security challenges. The risk management framework encompasses two steps: risk assessment and risk mitigation. The risk assessment step aims to quantify the risk, whereas the risk mitigation step focuses on designing mitigation strategies. This thesis leverages the risk management framework to analyze and design NCSs that are resilient to cyber-attacks. In particular, this thesis aims to address the following research challenges. Firstly, we aim to assess the risk of attack scenarios that are realistic (risk assessment step). In particular, we consider adversaries and operators with different levels of knowledge about the NCS. For instance, an adversary or operator may possess complete knowledge of the system dynamics or have only partial knowledge with varying degrees of uncertainty. Hence, we describe a systematic approach to assess the risk considering the interplay between the knowledge levels of adversaries and operators.Secondly, we aim to design the NCS to minimize the risk of attacks (risk mitigation step). We explore three different strategies to minimize the risk: (a) controller/detector design, (b) security measure allocation, and (c) system architecture design. In the first strategy, we design the controller and detector gains to minimize the risk of attacks. Here, risk is characterized by the performance loss caused by stealthy attacks on the NCS. In the second strategy, we consider a distributed NCS where certain distributed devices can be secured from attacks by deploying secure sensors and actuators. Then, we aim to strategically determine the devices to secure and mitigate the risk of attacks effectively. Finally, inspired by digital watermarking, we explore the idea of introducing watermarks in NCS to detect attacks efficiently. Throughout the thesis, we provide various numerical examples to depict the efficacy of risk assessment and risk mitigation algorithms. We also provide numerous discussions and avenues for future research directions.
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| 46. |
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| 47. |
-
Directions in Mathematical Systems : Theory and Optimization
- 2003
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- This volume provides a compilation of recent contributions on feedback and robust control, modeling, estimation and filtering. They were presented on the occasion of the sixtieth birthday of Anders Lindquist, who has delivered fundamental contributions to the fields of systems, signals and control for more than three decades. His contributions include seminal work on the role of splitting subspaces in stochastic realization theory, on the partial realization problem for both deterministic and stochastic systems, on the solution of the rational covariance extension problem and on system identification. Lindquist's research includes the development of fast filtering algorithms, leading to a nonlinear dynamical system which computes spectral factors in its steady state, and which provide an alternate, linear in the dimension of the state space, to computing the Kalman gain from a matrix Riccati equation. He established the separation principle for stochastic function differential equations, including some fundamental work on optimal control for stochastic systems with time lags. His recent work on a complete parameterization of all rational solutions to the Nevanlinna-Pick problem is providing a new approach to robust control design.
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| 48. |
- Dirr, Gunther, et al.
(författare)
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Separable Lyapunov functions for monotone systems: Constructions and limitations.
- 2015
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Ingår i: Discrete and Continuous Dynamical Systems. Series B. - : American Institute of Mathematical Sciences (AIMS). - 1553-524X .- 1531-3492. ; 20:8, s. 2497-2526
-
Tidskriftsartikel (refereegranskat)abstract
- For monotone systems evolving on the positive orthant, two types of Lyapunov functions are considered: Sum- and max-separable Lyapunov functions. One can be written as a sum, the other as a maximum of functions of scalar arguments. Several constructive existence results for both types are given. Notably, one construction provides a max-separable Lyapunov function that is defined at least on an arbitrarily large compact set, based on little more than the knowledge about one trajectory. Another construction for a class of planar systems yields a global sum-separable Lyapunov function, provided the right hand side satisfies a small-gain type condition. A number of examples demonstrate these methods and shed light on the relation between the shape of sublevel sets and the right hand side of the system equation. Negative examples show that there are indeed globally asymptotically stable systems that do not admit either type of Lyapunov function.
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| 49. |
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Distributed Decision Making and Control
- 2012
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Distributed Decision Making and Control is a mathematical treatment of relevant problems in distributed control, decision and multi-agent systems, The research reported was prompted by the recent rapid development in large-scale networked and embedded systems and communications. One of the main reasons for the growing complexity in such systems is the dynamics introduced by computation and communication delays. Reliability, predictability, and efficient utilization of processing power and network resources are central issues and the new theory and design methods presented here are needed to analyze and optimize the complex interactions that arise between controllers, plants and networks. The text also helps to meet requirements arising from industrial practice for a more systematic approach to the design of distributed control structures and corresponding information interfaces Theory for coordination of many different control units is closely related to economics and game theory network uses being dictated by congestion-based pricing of a given pathway. The text extends existing methods which represent pricing mechanisms as Lagrange multipliers to distributed optimization in a dynamic setting. In Distributed Decision Making and Control, the main theme is distributed decision making and control with contributions to a general theory and methodology for control of complex engineering systems in engineering, economics and logistics. This includes scalable methods and tools for modeling, analysis and control synthesis, as well as reliable implementations using networked embedded systems. Academic researchers and graduate students in control science, system theory, and mathematical economics and logistics will find mcu to interest them in this collection, first presented orally by the contributors during a sequence of workshops organized in Spring 2010 by the Lund Center for Control of Complex Engineering Systems, a Linnaeus Center at Lund University, Sweden.
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| 50. |
- Doan, Minh Dang, et al.
(författare)
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A distributed accelerated gradient algorithm for distributed model predictive control of a hydro power valley
- 2013
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Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661. ; 21:11, s. 1594-1605
-
Tidskriftsartikel (refereegranskat)abstract
- A distributed model predictive control (DMPC) approach based on distributed optimization is applied to the power reference tracking problem of a hydro power valley (HPV) system. The applied optimization algorithm is based on accelerated gradient methods and achieves a convergence rate of O(1/k^2), where k is the iteration number. Major challenges in the control of the HPV include a nonlinear and large-scale model, non-smoothness in the power-production functions, and a globally coupled cost function that prevents distributed schemes to be applied directly. We propose a linearization and approximation approach that accommodates the proposed the DMPC framework and provides very similar performance compared to a centralized solution in simulations. The provided numerical studies also suggest that for the sparsely interconnected system at hand, the distributed algorithm we propose is faster than a centralized state-of-the-art solver such as CPLEX.
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