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1.	Bengtsson, Johan, et al. (författare) Control of Homogeneous Charge Compression Ignition (HCCI) Engine Dynamics 2004 Ingår i: 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 Konferensbidrag (refereegranskat)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.
2.	Robertsson, Anders, et al. (författare) Design and evaluation of load control in web-server systems 2004 Ingår i: Proceedings of the 2004 American Control Conference, ACC : June 30 - July 2, 2004, Boston Sheraton Hotel, Boston, Massachusetts. - 0743-1619. - 0780383354 ; , s. 1980-1985 Konferensbidrag (refereegranskat)abstract Nonlinear discrete-time modeling of a Web server system is investigated. Server systems typically contain nonlinearities such as saturations and bounded queue lengths. The incoming traffic and service rates are best modeled by stochastic processes, well described and analyzed by queuing theory. Here, we develop and validate a control theoretic model of a general single server queue, a so-called G/G/1-system. Based on the nonlinear system model, design of admission controllers are presented and the closed loop stability is analyzed. The behavior of the server model is verified with respect to queue theoretic models. Finally, experimental evaluation is performed on an Apache Web server in a laboratory network. A traffic generator is used to represent client requests. The control of the Apache server has been re-written to implement our algorithms. We show that the control theoretic model aligns well with the experiments on the Web-server. Measurements in the laboratory setup show the robustness of the implemented controller, and how it corresponds to the results from the theoretical analysis and the simulations.
3.	Sandberg, Henrik, et al. (författare) Frequency-Domain Analysis of Linear Time-Periodic Systems 2004 Ingår i: Proceedings of the 2004 American Control Conference.. - 0743-1619. - 0780383354 ; 4, s. 3357-3362 Konferensbidrag (refereegranskat)abstract In this paper we study how a system with a time-periodic impulse response may be expanded into a sum of modulated time-invariant systems. This allows us to define a linear frequency-response operator for periodic systems, called the harmonic transfer function (HTF). Similar frequency-response operators have been derived before for sampled-data systems and periodic finite-dimensional state-space systems. The HTF is an infinite-dimensional operator that captures the frequency coupling of a time-periodic system. The paper includes analysis of convergence of truncated HTFs. For this reason the concepts of input/output roll-off are developed and related to time-varying Markov parameters.
4.	Abdelzaher, Tarek, et al. (författare) Practical Application of Control Theory to Web Services 2004 Ingår i: Proceedings of the American Control Conference. - 0743-1619. ; 3, s. 1992-1997 Konferensbidrag (refereegranskat)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.
5.	Ali, Mohammad, 1982, et al. (författare) Model-Based Threat Assessment for Lane Guidance Systems 2011 Ingår i: American Control Conference. - 0743-1619. - 9781457700804 ; , s. 4586-4591 Konferensbidrag (refereegranskat)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.
6.	Almér, Stefan, et al. (författare) Global stability analysis of DC-DC converters using sampled-data modeling 2004 Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - 0780383354 ; , s. 4549-4554 Konferensbidrag (refereegranskat)abstract The paper presents stability analysis of a class of pulse-width modulated (PWM) systems which incorporates many different DC-DC converters. Two types of pulse-width modulation (digital and analog control) are considered. A procedure is developed for systematic search for Lyapunov functions. The state space is partitioned in such a way that stability is verified if a set of coupled Linear Matrix Inequalities (LMIs) is feasible. Global stability is considered as well as the computation of local regions of attraction.
7.	Andersson, Alina, et al. (författare) Analytic Parameterization of Stabilizing Controllers for the Surge Subsystem of the Moore-Greitzer Compressor Model 2013 Ingår i: Proc. 2013 American Control Conference (ACC2013). - 0743-1619. - 9781479901777 ; , s. 5257-5262 Konferensbidrag (refereegranskat)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.
8.	Bernhardsson, Bo, et al. (författare) A Simple But Rich Test Example for H∞-Optimal Control 1992 Ingår i: Proceedings of the American Control Conference. - 0743-1619. - 0780302109 ; 1, s. 745-746 Konferensbidrag (refereegranskat)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, et al. (författare) Models and Methodology for Optimal Vehicle Maneuvers Applied to a Hairpin Turn 2013 Ingår i: 2013 American Control Conference. - 0743-1619. - 9781479901777 ; , s. 2139-2146 Konferensbidrag (refereegranskat)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.
10.	Berntorp, Karl (författare) Particle Filter for Combined Wheel-Slip and Vehicle-Motion Estimation 2015 Ingår i: 2015 American Control Conference (ACC). - 0743-1619 .- 2378-5861. - 9781479917730 - 9781479986842 ; , s. 5414-5419 Konferensbidrag (refereegranskat)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.
11.	Berntorp, Karl, et al. (författare) Path Tracking with Obstacle Avoidance for Pseudo-Omnidirectional Mobile Robots Using Convex Optimization 2014 Ingår i: [Host publication title missing]. - 0743-1619. ; , s. 517-524 Konferensbidrag (refereegranskat)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.
12.	Campbell, S.L., et al. (författare) A numerical integrator for simulation of unstructured implicit models 2004 Ingår i: Proceedings of the 2004 American Control Conference. - 0743-1619. ; 6, s. 5647-5652 Konferensbidrag (refereegranskat)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.
13.	Chasparis, Georgios, et al. (författare) Distributed Management of CPU Resources for Time-Sensitive Applications 2013 Ingår i: [Host publication title missing]. - 0743-1619. ; , s. 5305-5312 Konferensbidrag (refereegranskat)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.
14.	Dahl, Ola, et al. (författare) Nonlinear and Adaptive Observers for Perspective Dynamic Systems 2007 Ingår i: Proceedings American Control Conference. - : IEEE. - 0743-1619. - 9781424409884 ; , s. 2230-2235 Konferensbidrag (refereegranskat)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.
15.	Falcone, Paolo, 1977, et al. (författare) A Hierarchical Model Predictive Control Framework for Autonomous Ground Vehicles 2008 Ingår i: American Control Conference. - 0743-1619. - 9781424420797 ; , s. 3719 - 3724 Konferensbidrag (refereegranskat)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. (författare) Combined Process Algebra and Petri Nets for Specification of Resource Booking Problems 2001 Ingår i: American Control Conference. - 0743-1619. - 0780364953 ; 6, s. 4949-4955 Konferensbidrag (refereegranskat)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.	Freidovich, Leonid, 1973-, et al. (författare) Comparison of logic-based switching control designs for a nonlinear system 2004 Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - 0780383354 ; , s. 1221-1222 Konferensbidrag (refereegranskat)abstract We consider an example of a second order nonlinear system with large parametric uncertainties. The two parameters of the system are assumed to belong to a finite set. The goal is to guarantee (practical) convergence of the system output to a given constant reference signal. Feedback linearization-based candidate controllers with pole placement are designed for each possible set of parameters. After that, we consider the design of a high-level logic-based supervisor to organize switching between these candidate controllers. Three different approaches are used and compared.
18.	Gattami, Ather, et al. (författare) A frequency domain condition for stability of interconnected MIMO systems 2004 Ingår i: Proceedings of the 2004 American Control Conference. - 0780383354 ; , s. 3723-3728 Konferensbidrag (refereegranskat)abstract Analysis of interconnected dynamical systems is considered. A framework for the analysis of stability of the interconnection is given. The results of Fax and Murray that studies the SISO-case for a constant interconnection matrix are generalized to the MIMO-case where arbitrary interconnection is allowed. The analysis shows the existence of a separation principle that is very useful in the sense of the simplicity for stability analysis. Stability could be checked graphically using a Nyquist-like criterion. The problem with time-delays and interconnection variation and robustness appear to be natural special cases of the general framework, and hence, simple stability criteria are derived easily
19.	Gattami, Ather, et al. (författare) Minimax Team Decision Problems 2007 Ingår i: ; , s. 4333-4338, s. 766-771 Konferensbidrag (refereegranskat)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.
20.	Giselsson, Pontus (författare) A generalized distributed accelerated gradient method for distributed model predictive control with iteration complexity bounds 2013 Ingår i: [Host publication title missing]. - 0743-1619. ; , s. 327-333 Konferensbidrag (refereegranskat)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.
21.	Giselsson, Pontus (författare) Optimal preconditioning and iteration complexity bounds for gradient-based optimization in model predictive control 2013 Ingår i: [Host publication title missing]. - 0743-1619. ; , s. 358-364 Konferensbidrag (refereegranskat)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.
22.	Giselsson, Pontus (författare) Output feedback distributed model predictive control with inherent robustness properties 2013 Ingår i: [Host publication title missing]. - 0743-1619. ; , s. 1691-1696 Konferensbidrag (refereegranskat)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.
23.	Greiff, Marcus, et al. (författare) Attitude Control on SU(2) : Stability, Robustness, and Similarities 2021 Ingår i: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1693-1699 Konferensbidrag (refereegranskat)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.
24.	Greiff, Marcus, et al. (författare) Tuning and Analysis of Geometric Tracking Controllers on SO(3) 2021 Ingår i: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1674-1680 Konferensbidrag (refereegranskat)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.
25.	Gustafsson, Fredrik, et al. (författare) Transmission Timing - A Control Approach to Distributed Uplink Scheduling in WCDMA 2004 Ingår i: Proceedings of Reglermöte 2004. - Linköping : Linköping University Electronic Press. ; , s. 1667-1672 vol.2 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Centralized control and coordination of the connections in a wireless network is not possible in practice. To keep the delay from measure-ment instants to actuating the decisions, distributed control is required. This paper focuses on the uplink (from mobiles to base stations) and dis-cusses distributing the decision of when and when not to transmit data (distributed scheduling) to the mobiles. The scheme, uplink transmission timing, utilizes mobile transmitter power control feedback from the base station receiver to determine whether the channel is favorable or not compared to the average channel condition. Thereby, the battery consumption and disturbing power to other connections are reduced. The algorithm can be described as a feedback control system. Some transient behaviors are analyzed using systems theory, and supported by wireless network simulations of a system with a WCDMA (Wideband Code Division Multiple Access) radio interface as in most 3G systems.
26.	Gäfvert, Magnus, et al. (författare) On the Effect of Transient Data-Errors in Controller Implementations 2003 Ingår i: Proceedings of the 2003 American Control Conference, vols 1-6. - 0743-1619. - 0780378962 ; 4, s. 3411-3416 Konferensbidrag (refereegranskat)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.
27.	Hansson, Anders, et al. (författare) Stability Analysis of Nonlinear Systems using Frozen Stationary Linearization 2004 Ingår i: Proceedings of the 2004 American Control Conference. - 0780383354 ; , s. 424-428 Konferensbidrag (refereegranskat)abstract This work discusses how to compute stability regions for nonlinear systems with slowly varying parameters using frozen stationary linearization. It is shown that larger stability regions can be obtained as compared to traditional approaches using recent stability results for linear parameter-varying systems.
28.	Hedegärd, Marcus, 1979, et al. (författare) Convex identification of models for asymmetric hysteresis 2014 Ingår i: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 4753-4758 Konferensbidrag (refereegranskat)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.
29.	Henningsson, Maria, et al. (författare) Dynamic Mapping of Diesel Engine through System Identification 2010 Ingår i: Proceedings of the 2010 American Control Conference. - 2378-5861 .- 0743-1619. - 9781424474264 - 9781424474271 ; , s. 3015-3020 Konferensbidrag (refereegranskat)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.
30.	Hosseini, Seyed Mehrdad, 1977, et al. (författare) Adaptive forward collision warning algorithm for automotive applications 2016 Ingår i: American Control Conference. - 0743-1619. - 9781467386821 ; 2016-July, s. 5982-5987 Konferensbidrag (refereegranskat)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.
31.	Hult, Robert, 1984, et al. (författare) An approximate solution to the optimal coordination problem for autonomous vehicles at intersections 2015 Ingår i: American Control Conference. - 0743-1619. - 9781479917730 ; 2015, s. 763-768 Konferensbidrag (refereegranskat)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.
32.	Ianelli, Luigi, et al. (författare) Dither shape in the averaging of switched systems 2004 Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - : IEEE. - 0780383354 ; , s. 5812-5817 Konferensbidrag (refereegranskat)abstract It was shown by Zames and Shneydor that a high-frequency dither of a quite arbitrary shape can be used to smooth the effective nonlinear sector of Lipschitz continuous feedback systems. Here it is shown that also systems with discontinuous nonlinearities can be smoothed using dither signals, as long as the amplitude distribution function of the dither is Lipschitz continuous.
33.	Iliev, Boyko, et al. (författare) Minimum-time sliding mode control for second-order systems 2004 Ingår i: Proceedings of the 2004 American control conference, 2004. - 0780383354 ; , s. 626-631 Konferensbidrag (refereegranskat)abstract Our approach for near time-optimal control is based on Takagi-Sugeno fuzzy model of the maximum slope SMC sliding surface as an adaptive technique for tuning the current slope of the sliding surface to the maximum feasible slope depending on the current state of system. The stability conditions of this method are proved and respective measures about the feasible maximum slope are presented. Experimental results demonstrate the system behaviour.
34.	Jorques Moreno, Carlos, et al. (författare) Modular Design and Integration of In-Cycle Closed-Loop Combustion Controllers for a Wide-Range of Operating Conditions 2021 Ingår i: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1875-1881 Konferensbidrag (refereegranskat)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.
35.	Kao, Chien-Ya, et al. (författare) A New Barrier Function for IQC Optimization Problems 2003 Ingår i: Proceedings of the American Control Conference. - 0743-1619. ; 5, s. 4281-4286 Konferensbidrag (refereegranskat)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.
36.	Karlsson, Rickard, 1970-, et al. (författare) Model-Based Statistical Tracking and Decision Making for Collision Avoidance Application 2004 Ingår i: Proceedings of the 2004 American Control Conference. - Linköping : Linköping University Electronic Press. - 0780383354 ; , s. 3435-3440 Konferensbidrag (refereegranskat)abstract A growing research topic within the automotive industry is active safety systems. These systems aim at helping the driver avoid or mitigate the consequences of an accident. In this paper a collision mitigation system that performs late braking is discussed. The brake decision is based on estimates from tracking sensors. We use a Bayesian approach, implementing an extended Kalman filter (EKF) and a particle filter to solve the tracking problem. The two filters are compared for different sensor noise distributions in a Monte Carlo simulation study. In particular a bi-modal Gaussian distribution is proposed to model measurement noise for normal driving. For ideal test conditions the noise probability density is derived from experimental data. The brake decision is based on a statistical hypothesis test, where collision risk is measured in terms of required acceleration to avoid collision. The particle filter method handles this test easily. Since the test is not analytically solvable a stochastic integration is performed for the EKF method. Both systems perform well in the simulation study under the assumed sensor accuracy. The particle filter based algorithm is also implemented in a real-time testbed and fulfilled the on-line requirements.
37.	Kergus, Pauline (författare) Data-driven control of infinite dimensional systems : Application to a continuous crystallizer 2021 Ingår i: 2021 American Control Conference, ACC 2021. - 0743-1619. - 9781665441971 ; 2021-May, s. 1438-1443 Konferensbidrag (refereegranskat)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.
38.	Kjaer, Martin Ansbjerg, et al. (författare) Analysis of Buffer Delay in Web-Server Control 2010 Ingår i: 2010 American Control Conference. - 0743-1619. ; , s. 1047-1052 Konferensbidrag (refereegranskat)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.
39.	Klintberg, Anton, 1989, et al. (författare) Theoretical bounds on the accuracy of state and parameter estimation for batteries 2017 Ingår i: American Control Conference. - 0743-1619. ; , s. 4035-4041 Konferensbidrag (refereegranskat)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.
40.	Kozma, A., et al. (författare) An improved distributed dual newton-CG method for convex quadratic programming problems 2014 Ingår i: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 2324-2329 Konferensbidrag (refereegranskat)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.
41.	Kuroiwa, Yohei, et al. (författare) H-infinity control with preview and delay 2004 Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - 0780383354 ; , s. 4794-4799 Konferensbidrag (refereegranskat)abstract An H-infinity control problem with simultaneous consideration of preview and delay is solved, where past signals and future signals are essential to describe. behaviors of the control system. Solvability conditions and complete controller parameterization are derived in the frequency domain within the scope of finite dimensional computations, that is, infinite dimensional aspects attributed to preview and delay are transformed to equivalent finite dimensional problems. The two-degree-of-freedom version is also considered.
42.	Köroglu, Hakan, 1971, et al. (författare) Controller Synthesis for a Homogenous Platoon under Leader and Predecessor Following Scheme 2014 Ingår i: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 1463-1468 Konferensbidrag (refereegranskat)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.
43.	Köroglu, Hakan, 1971 (författare) Improved Conditions for Observer-Based LPV Control with Guaranteed L2-Gain Performance 2014 Ingår i: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 3760-3765 Konferensbidrag (refereegranskat)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.
44.	Larsson, Viktor, 1984, et al. (författare) Benefit of Route Recognition in Energy Management of Plug-in Hybrid Electric Vehicles 2012 Ingår i: Proceedings of the American Control Conference. - : IEEE. - 0743-1619. - 9781457710940 ; , s. 1314-1320 Konferensbidrag (refereegranskat)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.
45.	Lessard, Laurent, et al. (författare) Optimal controller synthesis for the decentralized two-player problem with output feedback 2012 Ingår i: American Control Conference (ACC), 2012. - 0743-1619. - 9781457710957 ; , s. 6314-6321 Konferensbidrag (refereegranskat)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.
46.	Lewander, Magnus, et al. (författare) Steady state fuel consumption optimization through feedback control of estimated cylinder individual efficiency 2012 Ingår i: Proceedings of the 2012 American Control Conference. - 0743-1619 .- 2378-5861. - 9781457710957 - 9781457710964 ; , s. 4210-4214 Konferensbidrag (refereegranskat)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.
47.	Li, Yang, 1984, et al. (författare) A PDE Model Simplification Framework for All-Solid-State Batteries 2022 Ingår i: American Control Conference. - 0743-1619. ; 2022-June, s. 1775-1781 Konferensbidrag (refereegranskat)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.
48.	Lincoln, Bo (författare) Jitter Compensation in Digital Control Systems 2002 Ingår i: Proceedings of the 2002 American Control Conference, 2002. - 0743-1619. - 0780372980 ; 4, s. 2985-2990 Konferensbidrag (refereegranskat)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.
49.	Linderoth, Magnus, et al. (författare) Nonlinear lateral control strategy for nonholonomic vehicles 2008 Ingår i: American Control Conference. - 0743-1619. - 9781424420780 ; , s. 3219-3224 Konferensbidrag (refereegranskat)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.
50.	Ljung, Lennart, 1946- (författare) Integrated Frequency-Time Domain Tools for System Identification 2004 Ingår i: Proceedings of the 2004 American Control Conference. - 0780383354 ; , s. 5594-5599 Konferensbidrag (refereegranskat)abstract The duality between time and frequency domain methods for linear systems is well known. It plays a crucial role for example in control systems design, and the domains are thought of complementing rather than competing. Quite recently, the full interplay and duality between the two domains have been clear also in system identification applications. In this contribution, this duality is discussed. The emphasis is on how it can be used to create a software environment for linear system identification that is as transparent as possible with respect to the data domains.

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