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1.	Andersson, Alina, et al. (author) Analytic Parameterization of Stabilizing Controllers for the Surge Subsystem of the Moore-Greitzer Compressor Model 2013 In: Proc. 2013 American Control Conference (ACC2013). - 0743-1619. - 9781479901777 ; , s. 5257-5262 Conference paper (peer-reviewed)abstract This paper is based on a new procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. The new procedure is motivated by the challenges of output feedback control design for the 3-state Moore-Greitzer compressor model. First, we use conditions for stability of a transformed system and the associated matching conditions to find the data of the stabilizing controllers for the surge subsystem. Second, using the set of stabilizing controllers satisfying the given constraints for the closed-loop system with the dynamic output feedback controller we made optimization over the parameter set. We present the data of the stabilizing controllers and the new constraints for the corresponding parameters. The contributions in this paper are simplified conditions for the synthesis and optimization over the control parameter set.
2.	Berntorp, Karl, et al. (author) Models and Methodology for Optimal Vehicle Maneuvers Applied to a Hairpin Turn 2013 In: 2013 American Control Conference. - 0743-1619. - 9781479901777 ; , s. 2139-2146 Conference paper (peer-reviewed)abstract There is currently a strongly growing interest in obtaining optimal control solutions for vehicle maneuvers, both in order to understand optimal vehicle behavior and to devise improved safety systems, either by direct deployment of the solutions or by including mimicked driving techniques of professional drivers. However, it is nontrivial to find the right mix of models, formulations, and optimization tools to get useful results for the above purposes. Here, a platform is developed based on a state-of-the-art optimization tool together with adoption of existing vehicle models, where especially the tire models are in focus. A minimum-time formulation is chosen to the purpose of gaining insight in at-the-limit maneuvers, with the overall aim of possibly finding improved principles for future active safety systems. We present optimal maneuvers for different tire models with a common vehicle motion model, and the results are analyzed and discussed. Our main result is that a few-state single-track model combined with different tire models is able to replicate the behavior of experienced drivers. Further, we show that the different tire models give quantitatively different behavior in the optimal control of the vehicle in the maneuver.
3.	Luspay, T., et al. (author) Mean-square optimal control of Linear Parameter Varying systems 2013 In: American Control Conference. - 0743-1619. - 9781479901777 ; , s. 6084 - 6089 Conference paper (peer-reviewed)abstract The problem of designing parameter-dependent output feedback controllers by using inaccurate knowledge of the scheduling parameter is addressed in the paper. Discrete time Linear Parameter Varying (LPV) systems are considered with external scheduling variables corrupted by measurement noise. The paper investigates the optimal control of such LPV class in the quadratic mean-square sense. The solution of the controller design problem is obtained as a standard optimization problem subject to Linear Matrix Inequality (LMI) constraints. A comparative simulation example is given to illustrate the proposed methodology and underline the importance of embedding stochastic information in the LPV control design procedure.
4.	Stotsky, Alexander, 1960, et al. (author) Control of wind turbines: A tutorial on proactive perspectives 2013 In: American Control Conference. - : IEEE. - 0743-1619. - 9781479901777 ; , s. 3429-3436 Conference paper (peer-reviewed)abstract Recent achievements in the proactive turbine control1, based on the upwind speed measurements are described in a unified tutorial fashion (as an extension of the tutorial [1]), that in turn represents a systematic view of the control activity carried out within the Swedish Wind Power Technology Center (SWPTC). A new turbine control problem statement with constraints on blade loads is reviewed. This problem statement allows the design of a new class of simultaneous speed and pitch control strategies based on the preview measurements and look-ahead calculations. A generation of a piecewise constant desired pitch angle profile which is calculated using the turbine load prediction is reviewed in this paper as one of the most promising approaches. This in turn allows the reduction of the pitch actuation and the design of the collective pitch control strategy with the maximum possible actuation rate.
5.	Abdelzaher, Tarek, et al. (author) Practical Application of Control Theory to Web Services 2004 In: Proceedings of the American Control Conference. - 0743-1619. ; 3, s. 1992-1997 Conference paper (peer-reviewed)abstract This tutorial describes experiences with applying a control theoretical approach to achieving performance guarantees in Web servers, with emphasis on delay control. A model for the server is formulated and translated into a control problem formulation. Limitations of the control theoretic approach are identified that arise due to system non-linearities and modeling inaccuracies. Solutions are proposed that augment the feedback control framework with elements of scheduling and queuing theory. The theoretical results and QoS control loops presented by the authors are implemented in a middleware package, called ControlWare, which provides the software mechanisms and interfaces that allow control of real server performance. Implementation and performance of ControlWare is described.
6.	Ali, Mohammad, 1982, et al. (author) Model-Based Threat Assessment for Lane Guidance Systems 2011 In: American Control Conference. - 0743-1619. - 9781457700804 ; , s. 4586-4591 Conference paper (peer-reviewed)abstract This paper considers a threat assessment problem in a lane guidance application for semi-autonomous vehicles. In particular, in order to issue an autonomous assisting intervention, we assess the vehicle’s ability to safely travel along a path subject to limitations arising from the vehicle’s dynamics and the driver’s ability.We first introduce a set of constraints describing “safedriving”. For the specific lane guidance application considered in this paper, the constraints are set by the lane boundaries and the vehicle’s stability limits. We then formulate the threat assessment problem as a constraints satisfaction problem over a finite time horizon, solved by resorting to reachabililty analysisand invariant set theory.Validation with experimental data demonstrates the capability of the proposed threat assessment method of predicting vehicle instability or crossing of the lane boundaries.
7.	Bengtsson, Johan, et al. (author) Control of Homogeneous Charge Compression Ignition (HCCI) Engine Dynamics 2004 In: Proceedings of the 2004 American Control Conference, ACC : June 30 - July 2, 2004, Boston Sheraton Hotel, Boston, Massachusetts. - 0743-1619. - 0780383354 ; 5, s. 4048-4053 Conference paper (peer-reviewed)abstract The Homogeneous Charge Compression Ignition (HCCI) combustionconcept lacks direct ignition timing control, instead the autoignition depends on the operating condition. Since auto ignition of ahomogeneous mixture is very sensitive to operating conditions, a fastcombustion timing control is necessary for reliable operation. Hence,feedback is needed and the crank angle of 50% burnt (CA50) has provedto be a reliable feedback indicator of on-going combustion inpractice. CA50 or other methods for detecting on-going cylinderpressure used in the feedback control of a HCCI engine all rely onpressure sensors. This paper presents a newcandidate for control of HCCI engine by using the electronicconductive properties in the reaction zone. This phenomenon is calledion current. This paper perform combustion timing control based on ioncurrent and compare it with control based on pressure sensor. Thecombustion timing control is performed on cycle-to-cycle basis and the engine is a one-cylinder version of a heavy duty engine equipped with a port injection system using dual fuels.
8.	Bernhardsson, Bo, et al. (author) A Simple But Rich Test Example for H∞-Optimal Control 1992 In: Proceedings of the American Control Conference. - 0743-1619. - 0780302109 ; 1, s. 745-746 Conference paper (peer-reviewed)abstract A simple second order feed-forward disturbance attenuation problem is analyzed. The problem has one free parameter, the control weight ρ in the loss function. It is found that controller structure and uniqueness for H∞-control, in the optimal case, changes when ρ is varied. Sensitivity to initial conditions is also drastically changed. The example is simple enough to allow a solution by formula manipulation, but is rich enough to give physically reasonable controllers and insight into the behavior of both state-space and polynomial H∞-methods at optimality. Details can be found in [6].
9.	Berntorp, Karl (author) Particle Filter for Combined Wheel-Slip and Vehicle-Motion Estimation 2015 In: 2015 American Control Conference (ACC). - 0743-1619 .- 2378-5861. - 9781479917730 - 9781479986842 ; , s. 5414-5419 Conference paper (peer-reviewed)abstract The vehicle-estimation problem is approached by fusing measurements from wheel encoders, an inertial measurement unit, and (optionally) a global positioning system in a Rao-Blackwellized particle filter. In total 14 states are estimated, including key variables in active safety systems, such as longitudinal velocity, roll angle, and wheel slip for all four wheels. The method only relies on kinematic relationships. We present experimental data for one test scenario, using a Volkswagen Golf equipped with state-of-the-art sensors for determining ground truth. We report highly promising results, even for periods of combined aggressive cornering and braking.
10.	Berntorp, Karl, et al. (author) Path Tracking with Obstacle Avoidance for Pseudo-Omnidirectional Mobile Robots Using Convex Optimization 2014 In: [Host publication title missing]. - 0743-1619. ; , s. 517-524 Conference paper (peer-reviewed)abstract We consider the problem of trajectory generation for time-optimal path tracking for the class of pseudo-omnidirectional mobile robots. An Euler-Lagrange model of the robot dynamics is derived, and by writing it on special form a convex reformulation of the path-tracking problem can be utilized. This enables the use and regeneration of time-optimal trajectories during runtime. The proposed approach also incorporates avoidance of moving obstacles, which are unknown a priori. Using sensor data, objects along the desired path are detected. Subsequently, a new path is planned and the corresponding time-optimal trajectory is found. The robustness of the method and its sensitivity to model errors are analyzed and discussed with extensive simulation results. Moreover, we verify the approach by successful execution on a physical setup.
11.	Campbell, S.L., et al. (author) A numerical integrator for simulation of unstructured implicit models 2004 In: Proceedings of the 2004 American Control Conference. - 0743-1619. ; 6, s. 5647-5652 Conference paper (peer-reviewed)abstract Object oriented modeling naturally leads to implicitly defined dynamical systems or, as they are also called, differential algebraic equations (DAEs). Most existing DAE integrators require the equations defining the dynamical system to have a special structure. Progress on the development of a new integrator for general unstructured DAEs is presented. The new integrator is called UCP. Computational tests are given to show that the new method can successfully integrate problems that other methods have trouble with.
12.	Chasparis, Georgios, et al. (author) Distributed Management of CPU Resources for Time-Sensitive Applications 2013 In: [Host publication title missing]. - 0743-1619. ; , s. 5305-5312 Conference paper (peer-reviewed)abstract The number of applications sharing the same embedded device is increasing dramatically. Very efficient mechanisms (resource managers) for assigning the CPU time to all demanding applications are needed. Unfortunately, existing optimization-based resource managers consume too much resource themselves. In this paper, we address the problem of distributed convergence to fair allocation of CPU resources for time-sensitive applications. We propose a novel resource management framework where both applications and the resource manager act independently trying to maximize their own performance measure according to a utility-based adjustment process. Contrary to prior work on centralized optimization schemes, the proposed framework exhibits adaptivity and robustness to changes both in the number and nature of applications, while it assumes minimum information available to both applications and the resource manager. It is shown analytically that fair resource allocation can be achieved through the proposed adjustment process when the CPU is overloaded. Experiments using the TrueTime Matlab toolbox show the validity of the proposed approach.
13.	Dahl, Ola, et al. (author) Nonlinear and Adaptive Observers for Perspective Dynamic Systems 2007 In: Proceedings American Control Conference. - : IEEE. - 0743-1619. - 9781424409884 ; , s. 2230-2235 Conference paper (peer-reviewed)abstract Estimation of 3D structure and motion from 2D images in computer vision systems can be performed using a dynamic system, often referred to as a perspective dynamic system. This paper presents a novel parametrization of the nonlinear perspective dynamic system, from which different estimators for rigid body structure as well as motion can be derived in a straightforward manner. The parametrization allows a structure estimator to be formulated as a nonlinear observer which estimates 3D position, assuming knowledge of angular and linear velocities. The observer performance is demonstrated using simulation examples, where it is also shown how a time scaling parameter can be used to tune the transient response. The parametrization also allows a motion estimator to be formulated as an adaptive observer, estimating angular velocity and 3D position assuming knowledge of the linear velocity. This is demonstrated by deriving an estimator and illustrating its performance in a simulation example. The presented investigations and simulations indicate that the parametrization has a potential for future development of estimators for structure as well as motion in perspective dynamic systems, and for the investigation of similarities and differences in comparison to discrete, projective geometry based, methods.
14.	Durr, H. -B, et al. (author) Obstacle avoidance for an extremum seeking system using a navigation function 2013 In: Proceedings of the American Control Conference 2013. - : AACC American Automatic Control Council. - 9781479901777 ; , s. 4062-4067 Conference paper (peer-reviewed)abstract The problem of autonomously steering a vehicle to a destination point, while avoiding obstacles, is considered. The vehicle is modeled as a single-integrator in the plane and it is assumed that the obstacles are unknown a priori. The control law is an extremum seeking algorithm, which steers the vehicle to the minimum of a navigation function. In this framework, obstacle avoidance and practical uniform convergence to a destination point for almost all initial conditions is proven. The theoretic results are illustrated using numerical examples.
15.	Falcone, Paolo, 1977, et al. (author) A Hierarchical Model Predictive Control Framework for Autonomous Ground Vehicles 2008 In: American Control Conference. - 0743-1619. - 9781424420797 ; , s. 3719 - 3724 Conference paper (peer-reviewed)abstract A hierarchical framework based on Model Predictive Control (MPC) for autonomous vehicles is presented. We formulate a predictive control problem in order to best follow a given path by controlling the front steering angle while fulfilling various physical and design constraints.We start from the low-level active steering-controller presented in [3], [9] and integrate it with a high level trajectory planner. At both levels MPC design is used. At the high-level, a trajectory is computed on-line, in a receding horizon fashion, based on a simplified point-mass vehicle model. At the low-level a MPC controller computes the vehicle inputs in order to best follow the desired trajectory based on detailed nonlinear vehicle model.This article presents the approach, the method for implementing it, and successful preliminary simulative results on slippery roads at high entry speed.
16.	Falkman, Petter, 1972, et al. (author) Combined Process Algebra and Petri Nets for Specification of Resource Booking Problems 2001 In: American Control Conference. - 0743-1619. - 0780364953 ; 6, s. 4949-4955 Conference paper (peer-reviewed)abstract A modeling framework for general routing and resource booking problems is presented. The task is to specify desired routes for individual objects (products, data packets, vehicles), which are to be served by a number of shared resources (machines, computers, communication links). A high level language is presented in order to simplify the specification of desired routes. This modeling language combines Petri nets and process algebra. Process operators are introduced for specification of sequences, alternative choices, arbitrary ordered sequences and process synchronization. Multiple as well as alternative resources are easily specified utilizing sets of resources. These sets and operators imply a very compact and efficient representation of complex routing specifications. In fact, the representation is suitable for verification and synthesis based on symbolic tools such as BDDs.
17.	Farokhi, Farhad, 1987-, et al. (author) Complexity Reduction for Parameter-Dependent Linear Systems 2013 In: 2013 American Control Conference (ACC). - : American Automatic Control Council. - 9781479901777 ; , s. 2624-2630 Conference paper (peer-reviewed)abstract We present a complexity reduction algorithm for a family of parameter-dependent linear systems when the system parameters belong to a compact semi-algebraic set. This algorithm potentially describes the underlying dynamical system with fewer parameters or state variables. To do so, it minimizes the distance (i.e., $H_\infty$-norm of the difference) between the original system and its reduced version. We present a sub-optimal solution to this problem using sum-of-squares optimization methods. We present the results for both continuous-time and discrete-time systems. Lastly, we illustrate the applicability of our proposed algorithm on numerical examples.
18.	Gattami, Ather, et al. (author) Minimax Team Decision Problems 2007 In: ; , s. 4333-4338, s. 766-771 Conference paper (peer-reviewed)abstract We consider the problem of distributed decision making in a quadratic game between a "team" of players and nature. Each player has limited information that could be different from the other players in the team. We show that if there is a solution to the minimax team problem, then the linear policies are optimal, and we show how to find the linear optimal solution by solving a linear matrix inequality. The result is used to solve the distributed H infinity control problem. It shows that the information structure restricted to exchange information with neighbours only, is enough to obtain a linear optimal feedback law.
19.	Giselsson, Pontus (author) A generalized distributed accelerated gradient method for distributed model predictive control with iteration complexity bounds 2013 In: [Host publication title missing]. - 0743-1619. ; , s. 327-333 Conference paper (peer-reviewed)abstract Most distributed optimization methods used for distributed model predictive control (DMPC) are gradient based. Gradient based optimization algorithms are known to have iterations of low complexity. However, the number of iterations needed to achieve satisfactory accuracy might be significant. This is not a desirable characteristic for distributed optimization in distributed model predictive control. Rather, the number of iterations should be kept low to reduce communication requirements, while the complexity within an iteration can be significant. By incorporating Hessian information in a distributed accelerated gradient method in a well-defined manner, we are able to significantly reduce the number of iterations needed to achieve satisfactory accuracy in the solutions, compared to distributed methods that are strictly gradient-based. Further, we provide convergence rate results and iteration complexity bounds for the developed algorithm.
20.	Giselsson, Pontus (author) Optimal preconditioning and iteration complexity bounds for gradient-based optimization in model predictive control 2013 In: [Host publication title missing]. - 0743-1619. ; , s. 358-364 Conference paper (peer-reviewed)abstract In this paper, optimization problems arising in model predictive control (MPC) and in distributed MPC aresolved by applying a fast gradient method to the dual of the MPC optimization problem. Although the development of fast gradient methods has improved the convergence rate of gradient-based methods considerably, they are still sensitive to ill-conditioning of the problem data. Since similar optimization problems are solved several times in the MPC controller, the optimization data can be preconditioned offline to improve the convergence rate of the fast gradient method online. A natural approach to precondition the dual problem is to minimize the condition number of the Hessian matrix. However, in MPC the Hessian matrix usually becomes positive semi-definite only, i.e., the condition number is infinite and cannot be minimized. In this paper, we show how to optimally precondition the optimization data by solving a semidefinite program, where optimally refers to the preconditioning that minimizes an explicit iteration complexity bound. Although the iteration bounds can be crude, numerical examples show that the preconditioning can significantly reduce the number of iterations needed to achieve a prespecified accuracy of the solution.
21.	Giselsson, Pontus (author) Output feedback distributed model predictive control with inherent robustness properties 2013 In: [Host publication title missing]. - 0743-1619. ; , s. 1691-1696 Conference paper (peer-reviewed)abstract We consider robust output feedback distributed model predictive control (DMPC). The proposed controller is based on the results in [8] in which nominal stability and feasibility was proven for a DMPC-formulation without terminal constraint set or terminal cost in the optimization. We extend these results to show robust stability under state feedback as well as output feedback when dynamics and measurements are affected by bounded noise. The provided numerical example suggests that the region of attraction without terminal constraint set may be significantly larger than if a terminal constraint set is used.
22.	Greiff, Marcus, et al. (author) Attitude Control on SU(2) : Stability, Robustness, and Similarities 2021 In: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1693-1699 Conference paper (peer-reviewed)abstract This paper concerns trajectory tracking control of attitude dynamics configured on SU(2). Inspired by a popular geometric tracking controller on SO(3), differential geometric tools are used to derive both continuous and discontinuous attitude controllers on the SU(2) manifold, relating these to preexisting controllers operating with imaginary quaternion errors. Additionally, a robustness result is given for the controllers on SU(2), which is illustrated by simulation examples.
23.	Greiff, Marcus, et al. (author) Tuning and Analysis of Geometric Tracking Controllers on SO(3) 2021 In: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1674-1680 Conference paper (peer-reviewed)abstract This paper concerns the robustness of attitude controllers for dynamics configured on the SO(3) manifold and poses a set of bilinear matrix inequalities to find an optimal controller tuning with respect to (i) the ultimate bound of the error-state trajectories when perturbed by naturally arising disturbances, and (ii) the worst-case decay rate of the tracking errors. The presented optimization problem can be solved both to generate a robust tuning for experimental applications, and also to facilitate qualitative comparisons of different attitude controllers present in the literature. To solve the tuning problem, we propose an algorithm based on alternating semidefinite programming, with local linearizations of an upper bound of the associated cost function. The soundness of this approach is illustrated by comparison to an interior-point method. The algorithm is subsequently used to provide insights for the tuning of the considered controllers, and finally demonstrated by a closed-loop simulation example.
24.	Grip, H. F., et al. (author) Output synchronization for heterogeneous networks of non-introspective, non-right-invertible agents 2013 In: Proceedings of the American Control Conference 2013. - : American Automatic Control Council. - 9781479901777 ; , s. 5791-5796 Conference paper (peer-reviewed)abstract We consider the output synchronization problem for a heterogeneous network of linear agents. The agents are non-introspective, meaning that they do not have access to their own state or output; the only information available to each agent comes from the network, in the form of a linear combination of its output relative to that of neighboring agents. The basis for our study is a design previously presented by the authors, which was based on an additional assumption requiring the agents to be right-invertible. Here we dispense with the assumption of right-invertibility and instead introduce a new assumption based on solvability of a particular set of regulator equations.
25.	Gäfvert, Magnus, et al. (author) On the Effect of Transient Data-Errors in Controller Implementations 2003 In: Proceedings of the 2003 American Control Conference, vols 1-6. - 0743-1619. - 0780378962 ; 4, s. 3411-3416 Conference paper (peer-reviewed)abstract Computer-level faults leading to data errors in computations arepredicted to occur increasingly frequent in future microprocessors.This work discusses the impact of such errors on closed-loopperformance in implementations of digital control systems. A method torender a control system more robust to data errors by introducingartificial signal limits and then combine them with an anti-windupscheme is presented and exemplified. Accepted for publication.
26.	Hedegärd, Marcus, 1979, et al. (author) Convex identification of models for asymmetric hysteresis 2014 In: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 4753-4758 Conference paper (peer-reviewed)abstract The generalized Prandtl-Ishlinskii model (GPI) of hysteresis has a wide applicability, partly because of its capability of modelling highly asymmetric hysteresis. A disadvantage of the GPI models compared to, for example the Modified Prandtl-Ishlinskii models, has been that they have had to be identified using parametric non convex methods. Recently though, a method for non-parametric convex identification for an extended and more general GPI model was described, giving all model functions. Here, the method, which was based on input discrete equations, is briefly presented in terms of the corresponding input continuous equations. This extended model corresponds to a Preisach model and an explicit expression for this relation is derived. The method is directly applicable to data consisting of first order reversal curves, but in an application to an electrical substation equipment, it is shown that other kinds of data can also be used. The method gives significantly closer fit to this data than previous studies, and it demonstrates that non-equal left and right envelope functions are optimal.
27.	Henningsson, Maria, et al. (author) Dynamic Mapping of Diesel Engine through System Identification 2010 In: Proceedings of the 2010 American Control Conference. - 2378-5861 .- 0743-1619. - 9781424474264 - 9781424474271 ; , s. 3015-3020 Conference paper (peer-reviewed)abstract From a control design point of view, modern diesel engines are dynamic, nonlinear, MIMO systems. This paper presents a method to find low-complexity black-box dynamic models suitable for model predictive control (MPC) of NOx and soot emissions based on on-line emissions measurements. A four-input-five-output representation of the engine is considered, with fuel injection timing, fuel injection duration, exhaust gas recirculation (EGR) and variable geometry turbo (VGT) valve positions as inputs, and indicated mean effective pressure, combustion phasing, peak pressure derivative, NOx emissions, and soot emissions as outputs. Experimental data were collected on a six-cylinder heavy-duty engine at 30 operating points. The identification procedure starts by identifying local linear models at each operating point. To reduce the number of dynamic models necessary to describe the engine dynamics, Wiener models are introduced and a clustering algorithm is proposed. A resulting set of two to five dynamic models is shown to be able to predict all outputs at all operating points with good accuracy.
28.	Hosseini, Seyed Mehrdad, 1977, et al. (author) Adaptive forward collision warning algorithm for automotive applications 2016 In: American Control Conference. - 0743-1619. - 9781467386821 ; 2016-July, s. 5982-5987 Conference paper (peer-reviewed)abstract This paper proposes an adaptive collision warning algorithm (CWA) that supports the driver by issuing early warnings for collision avoidance without noticeably increasing the risk of false alarms in real traffic. This algorithm can also detect when an emergency intervention is necessary. Compared to existing CWAs, the proposed solution in this paper triggers alarms by solving a linear convex program using traffic data, road’s constraints and bicycle model dynamics, and by incorporating an adaptive (speed-dependent) warning threshold. A collision threat is detected by determining feasible steering trajectories without altering the vehicle’s longitudinal velocity.
29.	Hult, Robert, 1984, et al. (author) An approximate solution to the optimal coordination problem for autonomous vehicles at intersections 2015 In: American Control Conference. - 0743-1619. - 9781479917730 ; 2015, s. 763-768 Conference paper (peer-reviewed)abstract In this paper, we address the problem of optimal and safe coordination of autonomous vehicles through a traffic intersection. We state the problem as a finite time, constrained optimal control problem, a combinatorial optimization problem that is difficult to solve in real-time. A low complexity computational scheme is proposed, based on a hierarchical decomposition of the original optimal control formulation, where a central coordination problem is solved together with a number of local optimal control problems for each vehicle. We show how the proposed decomposition allows a reduction of the complexity of the central problem, provided that approximated parametric solutions of the local problems are available beforehand. We derive conditions for the construction of the parametric approximations and demonstrate the method with a numerical example.
30.	Ishizaki, T., et al. (author) Structured model reduction of interconnected linear systems based on singular perturbation 2013 In: Proceedings of the American Control Conference 2013. - : American Automatic Control Council. - 9781479901777 ; , s. 5524-5529 Conference paper (peer-reviewed)abstract This paper proposes a singular perturbation approximation that preserves system passivity and an interconnection topology among subsystems. In the first half of this paper, we develop a singular perturbation approximation valid for stable linear systems. Using the relation between the singular perturbation and the reciprocal transformation, we derive a tractable expression of the error system in the Laplace domain, which provides a novel insight to regulate the approximating quality of reduced models. Then in the second half, we develop a structured singular perturbation approximation that focuses on a class of interconnected systems. This structured approximation provides a reduced model that not only possesses fine approximating quality, but also preserves the original interconnection topology and system passivity.
31.	Jansson, Daniel, et al. (author) Visual stimulus design in parameter estimation of the human smooth pursuit system from eye-tracking data 2013 In: Proc. American Control Conference. - : American Automatic Control Council. - 9781479901777 ; , s. 887-892 Conference paper (peer-reviewed)
32.	Jorques Moreno, Carlos, et al. (author) Modular Design and Integration of In-Cycle Closed-Loop Combustion Controllers for a Wide-Range of Operating Conditions 2021 In: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1875-1881 Conference paper (peer-reviewed)abstract This paper investigates how multiple in-cycle closed-loop combustion controllers can be integrated for a seamless operation under a wide-range of operating conditions. The stochastic cyclic variations of the combustion can be successfully compensated by the adjustment of the fuel injection pulses within the same cycle. The feedback information and controllability obtained relies on the different operating conditions, emissions regulations and fuels. Various in-cycle closed-loop combustion controllers are found in the literature to overcome the numerous challenges of the combustion control. In this paper, the modularization for the controller design and their integration is investigated, and how the transition between the available information, control actions and control strategy affects the final combustion behaviour. The approach consists in the design of a finite-state machine that supervises the transition between virtual sensors and measurements, regulators and the possibility of additional fuel injections. The proposed approach was tested in a Scania D13 engine for a wide-range of operating conditions. The results confirm the improved controllability and reduced steady-state RMSE of the controlled parameters, with a smoother transition between set-points, regardless of operating conditions and fuel.
33.	Kao, Chien-Ya, et al. (author) A New Barrier Function for IQC Optimization Problems 2003 In: Proceedings of the American Control Conference. - 0743-1619. ; 5, s. 4281-4286 Conference paper (peer-reviewed)abstract In this paper, we propose a new barrier function for optimization problems with Integral Quadratic Constraints (IQCs). The new barrier function is used to construct an interior point algorithm which solves IQC optimization problems in a more efficient fashion. Numerical tests as well as worst-case computational complexity analysis are performed to evaluate the efficiency of the proposed algorithm.
34.	Katselis, Dimitrios, et al. (author) Efficient OOK/DS-CDMA Detection Threshold Selection 2013 In: 2013 American Control Conference (ACC). - : American Automatic Control Council. - 9781479901777 ; , s. 3523-3528 Conference paper (peer-reviewed)abstract A major constraint in deployments of wireless sensor networks (WSNs) is the energy consumption related to the battery lifetime of the network nodes. To this end, power efficient digital modulation techniques such as On-Off keying (OOK) are highly attractive. However, the OOK detection thresholds, namely the thresholds against which the received signals are compared to detect which bit is transmitted, must be carefully selected to minimize the bit error rate. This is challenging to accomplish in resource-limited nodes with constrained computational capabilities. In this paper, the system scenario considers simultaneously transmitting nodes in Rayleigh fading conditions. Various iterative algorithms to numerically select the detection thresholds are established. Convergence analysis accompanies these algorithms. Numerical simulations are provided to support the derived results and to compare the proposed algorithms. It is concluded that OOK modulation is beneficial in resource constrained WSNs provided that efficient optimization algorithms are employed for the threshold selection.
35.	Kergus, Pauline (author) Data-driven control of infinite dimensional systems : Application to a continuous crystallizer 2021 In: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1438-1443 Conference paper (peer-reviewed)abstract Controlling infinite dimensional models remains a challenging task for many practitioners since they are not suitable for traditional control design techniques or will result in a high-order controller too complex for implementation. Therefore, the model or the controller need to be reduced to an acceptable dimension, which is time-consuming, requires some expertise and may introduce numerical error. This paper tackles the control of such a system, namely a continuous crystallizer, and compares two different data-driven strategies: the first one is a structured robust technique while the other one, called L-DDC, is based on the Loewner interpolatory framework. Model/Controller reduction, Stability of linear systems, Control applications.
36.	Kjaer, Martin Ansbjerg, et al. (author) Analysis of Buffer Delay in Web-Server Control 2010 In: 2010 American Control Conference. - 0743-1619. ; , s. 1047-1052 Conference paper (peer-reviewed)abstract This paper addresses a problem related to control of web servers. Due to architectual issues, relevant measurements can only be taken over a limited part of the server system, which leaves the controller unaware of what happens in buffers proceeding the actual web-server (for instance, in the TCP/IP layers). In earlier presented work we modeled such a system and proved that the unmeasured buffering turned a measurement of an input disturbance into a state-dependent variable. In this paper we investigate how these new properties effect a traditional control design consisting of feedback in combination with a feed-forward mechanism. The stability analysis suggests that under certain circumstances, the system enters limit cycles due to the feedback mechanism introduced by the designed feed-forward controller. We verify the analysis by both simulations and experiments.
37.	Klintberg, Anton, 1989, et al. (author) Theoretical bounds on the accuracy of state and parameter estimation for batteries 2017 In: American Control Conference. - 0743-1619. ; , s. 4035-4041 Conference paper (peer-reviewed)abstract Today it is standard to use equivalent circuit models to describe the dynamic behavior of Li-ion vehicle batteries. The parameters and states change with operating point and are therefore continuously estimated using bayesian observers, though without knowing to what degree the performance can be improved. Posterior Cramér-Rao Lower Bounds (CRLBs) can be used to theoretically quantify the optimal accuracy of bayesian estimators. In this paper we apply this to a second-order nonlinear equivalent-circuit model of a lithium-ion battery. It is shown, by numerical calculations, how the posterior Cramér-Rao Lower Bounds depend on the amplitude and frequency of the current, and on the slope of the Open Circuit Voltage (OCV) curve. Furthermore, it is investigated how much the accuracy is reduced in combined estimation of the states and the resistance compared to when the resistance is perfectly known. More importantly, it is also shown that the Mean Square Errors (MSE) of an Extended Kalman Filter (EKF) are close to the posterior CRLBs, which means that, under the investigated circumstances, it is not possible to significantly reduce the MSEs by replacing the EKF by any other observer.
38.	Kozma, A., et al. (author) An improved distributed dual newton-CG method for convex quadratic programming problems 2014 In: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 2324-2329 Conference paper (peer-reviewed)abstract This paper considers the problem of solving Programs (QP) arising in the context of distributed optimization and optimal control. A dual decomposition approach is used, where the QP subproblems are solved locally, while the constraints coupling the different subsystems in the time and space domains are enforced by performing a distributed non-smooth Newton iteration on the dual variables. The iterative linear algebra method Conjugate Gradient (CG) is used to compute the dual Newton step. In this context, it has been observed that the dual Hessian can be singular when a poor initial guess for the dual variables is used, hence leading to a failure of the linear algebra. This paper studies this effect and proposes a constraint relaxation strategy to address the problem. It is both formally and experimentally shown that the relaxation prevents the dual Hessian singularity. Moreover, numerical experiments suggest that the proposed relaxation improves significantly the convergence of the Distributed Dual Newton-CG.
39.	Köroglu, Hakan, 1971, et al. (author) Controller Synthesis for a Homogenous Platoon under Leader and Predecessor Following Scheme 2014 In: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 1463-1468 Conference paper (peer-reviewed)abstract Synthesis of dynamic output-feedback controllers is considered in a homogenous platoon operating under the leader and predecessor following scheme. The problem is formulated as a multi-objective H∞-type synthesis in which the goal is to keep the worst-case spacing error variations induced by the maneuvers of the leader as small as possible, while also avoiding excessively large control inputs. Concerns about possible communication problems are also reflected in the problem formulation. Sufficient solvability conditions are then derived in the form of linear matrix inequalities, which also depend on a scalar parameter over which a line search has to be performed. It is also described how the transient behavior of the platoon can be shaped by a simple additional condition. The procedure is illustrated by some sample designs and simulations in the longitudinal control of vehicle platoons.
40.	Köroglu, Hakan, 1971 (author) Improved Conditions for Observer-Based LPV Control with Guaranteed L2-Gain Performance 2014 In: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 3760-3765 Conference paper (peer-reviewed)abstract Synthesis of observer-based LPV controllers is considered with a guaranteed upper bound on the worst-case energy gain from the disturbance input to the performance output. A potentially conservative solution was derived for this problem before based on LMI optimization accompanied with a line search over a scalar variable. A new solution is provided in this paper based on a similar optimization problem, which has a comparable level of off-line computational complexity. It is shown that the new method cannot be any more conservative than the existing one. It is also verified by an example that the new solution can actually provide less conservative results. Another desirable feature of the new solution is that it is bettersuited for multi-objective synthesis.
41.	Larsson, Christian, et al. (author) Generation of excitation signals with prescribed autocorrelation for input and output constrained systems 2013 In: 2013 American Control Conference (ACC). - : American Automatic Control Council. - 9781479901777 ; , s. 3918-3923 Conference paper (peer-reviewed)abstract This paper considers the problem of realizing an input signal with a desired autocorrelation sequence satisfying both input and output constraints for the system it is to be applied to. This is a important problem in system identification. Firstly, the properties of the identified model are highly dependent on the used excitation signal during the experiment and secondly, on real processes, due to actuator saturation and safety considerations, it is important to constrain the inputs and outputs of the process. The proposed method is formulated as a nonlinear model predictive control problem. In general this corresponds to solving a non-convex optimization problem. Here we show how this can be solved in one particular case. For this special case convergence is established for generation of pseudo-white noise. The performance of the algorithm is successfully verified by simulations for a few different autocorrelation sequences, with and without input and output constraints.
42.	Larsson, Viktor, 1984, et al. (author) Benefit of Route Recognition in Energy Management of Plug-in Hybrid Electric Vehicles 2012 In: Proceedings of the American Control Conference. - : IEEE. - 0743-1619. - 9781457710940 ; , s. 1314-1320 Conference paper (peer-reviewed)abstract This paper investigates the benefit of an energymanagement system that autonomously can recognize when aplug-in hybrid electric vehicle is driven along known commutingroutes. The presented route recognition algorithm comparesthe GPS trajectory of the ongoing trip with stored commutingroutes using the well known cross-correlation operation. If aroute is recognized the energy management system switchesfrom a charge depleting charge sustaining discharge strategyto a strategy where the battery discharge rate is adapted to thelength of the recognized route, thereby decreasing the averagedischarge current and the resistive losses.The proposed system is evaluated using simulations onone month of logged commuter driving data. The resultsfor an energy management system based on the equivalentconsumption minimization strategy indicate an overall fuel costreduction of 1.5% compared to an system that only utilize acharge depleting charge sustaining strategy.
43.	Lessard, Laurent, et al. (author) Optimal controller synthesis for the decentralized two-player problem with output feedback 2012 In: American Control Conference (ACC), 2012. - 0743-1619. - 9781457710957 ; , s. 6314-6321 Conference paper (peer-reviewed)abstract In this paper, we present a controller synthesis algorithm for a decentralized control problem. We consider an architecture in which there are two interconnected linear subsystems. Both controllers seek to optimize a global quadratic cost, despite having access to different subsets of the available measurements. Many special cases of this problem have previously been solved, most notably the state-feedback case. The generalization to output-feedback is nontrivial, as the classical separation principle does not hold. Herein, we present the first explicit state-space realization for an optimal controller for the general two-player problem.
44.	Lewander, Magnus, et al. (author) Steady state fuel consumption optimization through feedback control of estimated cylinder individual efficiency 2012 In: Proceedings of the 2012 American Control Conference. - 0743-1619 .- 2378-5861. - 9781457710957 - 9781457710964 ; , s. 4210-4214 Conference paper (peer-reviewed)abstract Engine efficiency is often controlled in an indirectway through combustion timing control. This requires a prioriknowledge of where to phase the combustion for differentoperating points and conditions. With cylinder individual efficiencyestimation, control strategies aiming directly at fuelconsumption optimization can be developed. It has previouslybeen shown that indicated efficiency can be estimated using thecylinder pressure trace. This paper presents a method to usethe estimated efficiency as a feedback variable in an extremumseeking control strategy for online steady state fuel consumptionoptimization. The experimental results show that the controllermanages to find the maximum brake torque region at the givenoperating point both with and without external excitation.
45.	Li, Yang, 1984, et al. (author) A PDE Model Simplification Framework for All-Solid-State Batteries 2022 In: American Control Conference. - 0743-1619. ; 2022-June, s. 1775-1781 Conference paper (peer-reviewed)abstract All-solid-state batteries (ASSBs) have attracted immense attention due to their superior thermal stability, improved power and energy densities, and prolonged cycle life. Their practical applications require accurate and computationally efficient models for the design and implementation of many onboard management algorithms, so that the safety, health, and cycling performance of ASSBs can be optimized under a wide range of operating conditions. A control-oriented modeling framework is thus established in this work by systematically simplifying a partial differential equation (PDE) based model of the ASSBs developed from underlying electrochemical principles. Compared to the original PDE model, the reduced-order models obtained with the proposed framework demonstrates high fidelity at significantly improved computational efficiency.
46.	Lincoln, Bo (author) Jitter Compensation in Digital Control Systems 2002 In: Proceedings of the 2002 American Control Conference, 2002. - 0743-1619. - 0780372980 ; 4, s. 2985-2990 Conference paper (peer-reviewed)abstract A method to compensate for time-varying, possibly random, delays (jitter) in digital control systems is presented. Using time-stampsfrom the control system, a linear compensator is designed asan add-on to an existing control system. Stability andperformance analysis is performed, and leads to frequency domainconditions. Therefore, loop-shaping can be used for thecompensator design. The design ofthe compensator can be done without a full process model.
47.	Linderoth, Magnus, et al. (author) Nonlinear lateral control strategy for nonholonomic vehicles 2008 In: American Control Conference. - 0743-1619. - 9781424420780 ; , s. 3219-3224 Conference paper (peer-reviewed)abstract This paper proposes an intuitive nonlinear lateral control strategy for trajectory tracking in autonomous nonholonomic vehicles. The controller has been implemented and verified in Alice, Team Caltech's contribution to the 2007 DARPA Urban Challenge competition for autonomous motorcars. A kinematic model is derived. The control law is described and analyzed. Results from simulations and field tests are given and evaluated. Finally, the key features of the proposed controller are reviewed, followed by a discussion of some limitations of the proposed strategy.
48.	Luspay, T., et al. (author) Freeway ramp metering: an LPV set theoretical analysis 2011 In: American Control Conference. - 0743-1619. - 9781457700804 ; , s. 733-738 Conference paper (peer-reviewed)abstract The paper contributes to the set theoretic analysis of freeway traffic flow control by ramp metering.From the generic and discrete time non-linear second-order macroscopic dynamics of freeway, first, an equivalent, quasi Linear Parameter Varying (LPV) representation is derived by steady-state centering and factorization. Second, a polytopic LPV model form is obtained from the quasi reformulation of the non-linear problem statement. The latter polytopic LPV form is then used for the computation and analysis of distur- bance invariant sets. This framework is able to characterize constrained sets of states which can be reached by pure ramp metering control input signal respectively becomes invariant under the effect of other measured and unmeasured inputs.The application of disturbance invariant set theory clearly quantifies the set of states being invariant under the polytopic LPV dynamics and other physical constraints regardless to the open- and closed-loop nature of the system.The proposed idea is fully based on the analysis of the (transformed) non-linear macroscopic system and aims at filling the gap between the traffic modelling and quantitative freeway ramp metering.
49.	Martins, Alexandre, et al. (author) Dynamic Management of Multiple Resources in Camera Surveillance Systems* 2021 In: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 - 9781728197043 ; 2021-May, s. 2061-2068 Conference paper (peer-reviewed)abstract Distributed camera surveillance systems typically consist of multiple cameras that need to store some fraction of their video streams in a central storage node. The disk space of this node as well as the network between the cameras and this central node constitute shared resources. In the paper the disk space allocation as well as the network bandwidth reservation are solved using techniques normally associated with process control. These include mid-range control and tracking-based control of global shared resources. The approach is evaluated by simulations.
50.	Mirkin, Boris, et al. (author) Adaptive Output-Feedback Control of MIMO Plants with Unknown, Time-Varying State Delay 2008 In: American Control Conference. - 0743-1619. - 9781424420797 ; , s. 4761 - 4766 Conference paper (peer-reviewed)abstract In this paper, we develop a simple model reference adaptive control (MRAC) scheme for a class of multi-inputmulti-output (MIMO) linear dynamic systems with unknown time-varying state delay which is also robust with respect to an external disturbance with unknown bound. A suitable Lyapunov-Krasovskii type functional with “virtual” gain is introduced to design the adaptation algorithms and to prove stability.

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