| 1. |
- Chistiakova, Tatiana, et al.
(författare)
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Input–output stability design of an ammonium based aeration controller for wastewater treatment
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 2964-2971
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Konferensbidrag (refereegranskat)abstract
- Ammonium feedback is commonly used for controlling the aeration in wastewater treatment plants having biological nitrogen removal. The paper proposes the use of a PI controller tuning method based on a simplified identified model with Hammerstein structure. The Hammerstein model accounts for the delay of the process caused by the settler, the multiple bioreactors dynamics and the main nonlinear process effects. The controller tuning method exploits the Popov inequality for a pre-computation of (a subset of) the stability region of the closed loop system as a function of the PI-controller parameters, quantified in terms of the maximum loop delay of the system. The controller parameters are selected in the computed stability region. In the numerical study, the plant is identified as a Hammerstein model using a recently published method, here extended to identify multiple bioreactor tank dynamics. The identification data is obtained from a high fidelity simulator, which is also used for evaluation of the proposed controller tuning method. The results show that the proposed procedure results in a PI-controller tuning with predictable stability properties and a good performance.
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| 2. |
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| 3. |
- Greiff, Marcus
(författare)
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A Time-Warping Transformation for Time-Optimal Movement in Differentially Flat Systems
- 2018
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Ingår i: Proceedings of the American Control Conference. - 9781538654286 ; 2018-June, s. 6723-6730
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Konferensbidrag (refereegranskat)abstract
- The notion of warping the rate of time is explored in the context of differentially flat systems to enable time-optimal motion by convex optimisation. Examples are given with systems configured on the special Euclidean groups SE(2) and SE(3), with and without differential constraints. The proposed method complements classical methods of motion planning, may be used in a real-time context with guarantees on time-optimality subject to constraints on the first two derivatives on the flat output trajectory and all time-warping derivatives. In addition, an iterative method is presented to find close-to-optimal solutions in the event of non-convex constraints.
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| 4. |
- Greiff, Marcus, et al.
(författare)
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Evaluation of the Discrete Time Feedback Particle Filter for IMU-Driven Systems Configured on SE(2)
- 2018
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Ingår i: Proceedings of the American Control Conference. - 9781538654286 ; 2018-June, s. 5683-5689
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Konferensbidrag (refereegranskat)abstract
- This paper evaluates the utility of the feedback particle filter (FPF) for state estimation of SE(2)-configured dynamics in a real-time context. The filter is implemented in discrete time to fuse gyroscopic-and accelerometer measurements with Ultra-Wideband (UWB) and camera measurements. With this state information, the FPF is compared to other common filters in terms of the estimate mean square error (MSE) and robustness to initial conditions. An analysis is done on how these metrics scale with utilization of computational resources, concluding that the FPF should be considered for embedded applications with CPUs on par with the Cortex M4 processor.
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| 5. |
- Guay, Martin, et al.
(författare)
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Dual mode extremum-seeking control via Lie-bracket averaging approximations
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - Piscataway, NJ : IEEE. - 9781538654293 - 9781538654286 - 9781538654279 ; , s. 2972-2977
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a dual mode extremum-seeking controller (ESC) design based on a Lie bracket averaging technique. The stability analysis demonstrates that the practical asymptotical stability of the unknown optimum can be achieved for autonomous and non-autonomous systems. The application of the technique for the solution of realtime optimization problem with time-varying optimum state trajectories is presented. A simulation study demonstrates the ability of the proposed technique to remove the input bias that results in the application of existing Lie bracket design techniques to dynamical control systems.
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| 6. |
- Ling, Gustav, et al.
(författare)
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Fuel-efficient Model Predictive Control for Heavy Duty Vehicle Platooning using Neural Networks
- 2018
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Ingår i: 2018 American Control Conference (ACC). - : IEEE. - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 3994-4001
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Konferensbidrag (refereegranskat)abstract
- The demand for fuel-efficient transport solutions are steadily increasing with the goal of reducing environmental impact and increasing efficiency. Heavy-Duty Vehicle (HDV) platooning is a promising concept where multiple HDVs drive together in a convoy with small intervehicular spacing. By doing this, the aerodynamic drag is reduced which in turn lowers fuel consumption. We propose a novel Model Predictive Control (MPC) framework for longitudinal control of the follower vehicle in a platoon consisting of two HDVs when no vehicle-to-vehicle communication is available. In the framework, the preceding vehicle's velocity profile is predicted using artificial neural networks which uses a topographic map of the road as input and is trained offline using synthetic data. The gear shifting and mass of consumed fuel for the controlled follower vehicle is modeled and used within the MPC controller. The efficiency of the proposed framework is verified in simulation examples and is benchmarked with a currently available control solution.
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| 7. |
- Ljungqvist, Oskar, 1990-, et al.
(författare)
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On stability for state-lattice trajectory tracking control
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC)<em></em>. - : IEEE. - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 5868-5875
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Konferensbidrag (refereegranskat)abstract
- In order to guarantee that a self-driving vehicle is behaving as expected, stability of the closed-loop system needs to be rigorously analyzed. The key components for the lowest levels of control in self-driving vehicles are the controlled vehicle, the low-level controller and the local planner.The local planner that is considered in this work constructs a feasible trajectory by combining a finite number of precomputed motions. When this local planner is considered, we show that the closed-loop system can be modeled as a nonlinear hybrid system. Based on this, we propose a novel method for analyzing the behavior of the tracking error, how to design the low-level controller and how to potentially impose constraints on the local planner, in order to guarantee that the tracking error is bounded and decays towards zero. The proposed method is applied on a truck and trailer system and the results are illustrated in two simulation examples.
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| 8. |
- Nylander, Tommi, et al.
(författare)
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Brownout(CC) : Cascaded Control for Bounding the Response Times of Cloud Applications
- 2018
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Ingår i: 2018 ANNUAL AMERICAN CONTROL CONFERENCE (ACC). - : IEEE. - 9781538654286 ; , s. 3354-3361
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Konferensbidrag (refereegranskat)abstract
- Cloud computing has emerged as an inexpensive and powerful computing paradigm, to the point that now even applications with hard deadlines are executed in the cloud. It may happen, due to unexpected events, that an application becomes popular and receives a lot of attention and client requests in a short period of time. Provisioning computing capacity for such applications is quite a difficult task, because content popularity cannot he easily predicted. One of the main problems in case content has to be served with a hard deadline is to ensure that this deadline is respected, even in the presence of popularity spikes. To this end, partial computation and graceful degradation were exploited, originating the brownout framework. Applications would degrade the user experience in the presence of load variations, to guarantee that deadlines are met. Two different control paradigms were applied to brownout: discrete-time control of optional content percentage over a period and event-based queue management. The first one had reasonable performance providing formal guarantees about the solution. The second one was able to improve the performance and keep the response time at the setpoint better, but suffered from the drawback of not providing formally grounded mathematical guarantees. In this work we combine the best of both worlds, providing a cascaded controller for brownout, based on a more precise model of the cloud application with respect to the original design. The Brownout(CC) controller achieves performance comparable with the event based version, without sacrificing formal guarantees.
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| 9. |
- Pates, Richard, et al.
(författare)
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Scale Free Bounds on the Amplification of Disturbances in Mass Chains
- 2018
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Ingår i: 2018 Annual American Control Conference, ACC 2018. - 9781538654286 ; 2018-June, s. 6002-6005
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Konferensbidrag (refereegranskat)abstract
- We give a method for designing a mechanical impedance to suppress the propagation of disturbances along a chain of masses. The key feature of our method is that it is scale free. This means that it can be used to give a single, fixed, design, with provable performance guarantees in mass chains of any length. We illustrate the approach by designing a bidirectional control law in a vehicle platoon in a manner that is independent of the number of vehicles in the platoon.
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| 10. |
- Rantzer, Anders
(författare)
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Concentration Bounds for Single Parameter Adaptive Control
- 2018
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Ingår i: Proceedings of American Control Conference. - 9781538654286 ; 2018-June, s. 1862-1866
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to analyse transient dynamics in adaptive control using statistical concentration bounds. For maximal clarity, the study is limited to a linear first order system with a single uncertain parameter. Two types of bounds are given: First we prove probabilistic bounds on the parameter estimation error as a function of time. In particular, we prove that the estimation error has finite variance after three time steps and finite fourth moments after five time steps. These bounds are independent of how the parameter estimates are used for feedback. Secondly, we bound the “regret” as a function of time, i.e. the difference in control performance between a self-tuning adaptive controller and the best controller given full knowledge of the plant. The conservatism of the bounds is investigated through simulation.
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| 11. |
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| 12. |
- Valerio, Turri, 1987-, et al.
(författare)
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Fuel-optimal look-ahead adaptive cruise control for heavy-duty vehicles
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538654286 ; , s. 1841-1848
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the problem of how to optimally control a heavy-duty vehicle following another one, commonly referred as ad-hoc or non-cooperative platooning. The problem is formulated as an optimal control problem that exploits road topography information and the knowledge of the preceding vehicle speed trajectory to compute the optimal engine torque and gear request for the vehicle under control. The optimal control problem is implemented by dynamic programming and is tested in a simulation study that compares the performance of multiple longitudinal control strategies. The proposed look-ahead adaptive cruise controller is able to achieve fuel saving up to 7% with respect to the use of a reference vehicle-following controller, by combining the benefits of adjusting the inter-vehicular distance according to the future slope with those of alternating phases of throttling and freewheeling (driving in neutral gear).
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| 13. |
- Wågberg, Johan, et al.
(författare)
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Regularized parametric system identification : a decision-theoretic formulation
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : IEEE. - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 1895-1900
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Konferensbidrag (refereegranskat)abstract
- Parametric prediction error methods constitute a classical approach to the identification of linear dynamic systems with excellent large-sample properties. A more recent regularized approach, inspired by machine learning and Bayesian methods, has also gained attention. Methods based on this approach estimate the system impulse response with excellent small-sample properties. In several applications, however, it is desirable to obtain a compact representation of the system in the form of a parametric model. By viewing the identification of such models as a decision, we develop a decision-theoretic formulation of the parametric system identification problem that bridges the gap between the classical and regularized approaches above. Using the output-error model class as an illustration, we show that this decision-theoretic approach leads to a regularized method that is robust to small sample-sizes as well as overparameterization.
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| 14. |
- Xu, Yang, et al.
(författare)
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Jitter-Robust LQG Control and Real-Time Scheduling Co-Design
- 2018
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Ingår i: Proceedings of the American Control Conference. - 9781538654286 ; 2018-June, s. 3189-3196
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Konferensbidrag (refereegranskat)abstract
- In real-time control systems, varying task response times may lead to delays and jitter in the delays in the feedback control loops, which adversely affects both performance and robustness. Standard LQG control design does not give any guarantees on robustness, while robust control design methods often do not handle controller timing uncertainty. We propose a sampled-data controller synthesis method that minimizes an LQG cost function subject to a jitter margin constraint. By robustifying the LQG controller we are able to retain good stability margins under delay and jitter, while typically paying a small price in terms of nominal performance. We also present a co-design procedure that assigns optimal priorities and sampling periods to a set of controllers based on their performance characteristics and jitter sensitivity. The procedure is evaluated on randomized plant sets, showing an improvement over state-of-the-art methods.
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| 15. |
- Yasini, Sholeh, et al.
(författare)
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Counterexamples to parametric convergence in recursive networked identification
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 258-264
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Konferensbidrag (refereegranskat)abstract
- This paper studies a condition for global parametric convergence of a recursive identification algorithm with an output quantizer. The problem is addressed by an analytic calculation of the associated ODE for a low order test model. The ODE is then analysed numerically to investigate the possibilities for proving parametric convergence. The main contribution of the paper shows that a monotone quantizer is not a necessary condition for global parametric convergence to the true parameter vector w.p.1.
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| 16. |
- Yu, Pian, et al.
(författare)
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Explicit computation of sampling period in periodic event-triggered multi-agent control
- 2018
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Ingår i: Proceedings of the American Control Conference. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538654286 ; , s. 3038-3043
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the synchronization of nonlinear sampled-data multi-agent systems. The purpose is to obtain an explicit formula for the maximum allowable sampling period (MASP) that guarantees exponential synchronization. Two implementation scenarios are considered. We first propose an approach on finding the MASP for periodic time-triggered sampled-data control. Then, a periodic event-triggered communication and control strategy is formulated, where a communication function and a control function are designed for each agent to determine whether or not the sampled data or the control input should be transmitted at each sampling instant. It is shown that there is a tradeoff between the sampling frequency and the convergence performance. The theoretical results are illustrated in simulations.
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