| 1. |
- Andreasson, Martin, et al.
(författare)
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Correlated Failures of Power Systems : Analysis of the Nordic Grid
- 2011
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Ingår i: Preprints of Workshop on Foundations of Dependable and Secure Cyber-Physical Systems.
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Konferensbidrag (refereegranskat)abstract
- In this work we have analyzed the effectsof correlated failures of power lines on the total systemload shed. The total system load shed is determined bysolving the optimal load shedding problem, which is thesystem operator’s best response to a system failure.We haveintroduced a Monte Carlo based simulation framework forestimating the statistics of the system load shed as a functionof stochastic network parameters, and provide explicitguarantees on the sampling accuracy. This framework hasbeen applied to a 470 bus model of the Nordic power systemand a correlated Bernoulli failure model. It has been foundthat increased correlations between Bernoulli failures ofpower lines can dramatically increase the expected valueas well as the variance of the system load shed.
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| 2. |
- Burden, Sam, et al.
(författare)
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Parameter Identification Near Periodic Orbits of Hybrid Dynamical Systems
- 2012
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Ingår i: Proceedings of the 16th IFAC Symposium on System Identification. - 9783902823069 ; , s. 1197-1202
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Konferensbidrag (refereegranskat)abstract
- We present a novel identification framework that enables the use of first-order methods when estimating model parameters near a periodic orbit of a hybrid dynamical system. The proposed method reduces the space of initial conditions to a smooth manifold that contains the hybrid dynamics near the periodic orbit while maintaining the parametric dependence of the original hybrid model. First-order methods apply on this subsystem to minimize average prediction error, thus identifying parameters for the original hybrid system. We implement the technique and provide simulation results for a hybrid model relevant to terrestrial locomotion.
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| 3. |
- Fisac, Jaime F., et al.
(författare)
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Hierarchical Game-Theoretic Planning for Autonomous Vehicles
- 2019
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Ingår i: 2019 International Conference on Robotics and Automation, (ICRA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538660263 ; , s. 9590-9596
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Konferensbidrag (refereegranskat)abstract
- The actions of an autonomous vehicle on the road affect and are affected by those of other drivers, whether overtaking, negotiating a merge, or avoiding an accident. This mutual dependence, best captured by dynamic game theory, creates a strong coupling between the vehicle's planning and its predictions of other drivers' behavior, and constitutes an open problem with direct implications on the safety and viability of autonomous driving technology. Unfortunately, dynamic games are too computationally demanding to meet the real-time constraints of autonomous driving in its continuous state and action space. In this paper, we introduce a novel game-theoretic trajectory planning algorithm for autonomous driving, that enables real-time performance by hierarchically decomposing the underlying dynamic game into a long-horizon "strategic" game with simplified dynamics and full information structure, and a short-horizon "tactical" game with full dynamics and a simplified information structure. The value of the strategic game is used to guide the tactical planning, implicitly extending the planning horizon, pushing the local trajectory optimization closer to global solutions, and, most importantly, quantitatively accounting for the autonomous vehicle and the human driver's ability and incentives to influence each other. In addition, our approach admits non-deterministic models of human decision-making, rather than relying on perfectly rational predictions. Our results showcase richer, safer, and more effective autonomous behavior in comparison to existing techniques.
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| 4. |
- Hu, Jianghai, et al.
(författare)
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Hybrid geodesics as optimal solutions to the collision-free motion planning problem
- 2001
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Ingår i: Hybrid Systems. - : Springer Berlin/Heidelberg. ; , s. 305-318
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Bokkapitel (refereegranskat)abstract
- In this paper we address the problem of designing energy minimizing collision-free maneuvers for multiple agents moving on a plane. We show that the problem is equivalent to that of nding the shortest geodesic in a certain manifold with nonsmooth boundary. This allows us to prove that the optimal maneuvers are C1by introducing the concept of u-convex manifolds. Moreover, due to the nature of the optimal maneuvers, the problem can be formulated as an optimal control problem for a certain hybrid system whose discrete states consist of dierent \contact graphs". We determine the analytic expression for the optimal maneuvers in the two agents case. For the three agents case, we derive the dynamics of the optimal maneuvers within each discrete state. This together with the fact that an optimal maneuver is a C1con-catenation of segments associated with dierent discrete states gives a characterization of the optimal solutions in the three agents case.
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| 5. |
- Johansson, Karl Henrik, et al.
(författare)
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Modeling of hybrid systems
- 2004
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Ingår i: Encyclopedia of Life Support Systems (EOLSS), Theme 6.43: Control Systems, Robotics and Automation. - : Unesco.
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Bokkapitel (refereegranskat)abstract
- The distinguishing characteristic of hybrid systems is the interaction between a continuous-time and a discrete-event component. By modeling these different components using differential equations and finite state automata, it is possible to represent a wide range of phenomena present in physical and technological systems. This paper illustrates hybrid dynamics by several simple examples. Some of these examples illustrate properties of hybrid systems not present in purely continuous or purely discrete systems, while others illustrate application domains such as vehicle control and real-time systems. A mathematical model called a hybrid automaton is then introduced, to show how hybrid dynamics can be formally analyzed.
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| 6. |
- Lygeros, John, et al.
(författare)
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Continuity and invariance in hybrid automata
- 2001
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Ingår i: Proceedings of the 40th IEEE Conference on Decision and Control, 2001. - : IEEE. - 0780370619 ; , s. 340-345
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Konferensbidrag (refereegranskat)abstract
- Hybrid automata have been proposed as a language for modelling and analysing the interaction of digital and analogue dynamics in embedded computer systems. In the paper, hybrid automata are studied from a dynamical systems perspective. Extending earlier work on conditions for existence and uniqueness of executions of hybrid automata, we characterise a class of hybrid automata whose executions depend continuously on the initial state. The continuity conditions are subsequently used to derive an extension of LaSalle's principle for studying the stability of invariant sets of states of hybrid automata
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| 7. |
- Lygeros, John, et al.
(författare)
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On the existence of executions of hybrid automata
- 1999
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Ingår i: Proceedings of the 38th IEEE Conference on Decision and Control, 1999. - : IEEE. - 0780352505 ; , s. 2249-2254
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Konferensbidrag (refereegranskat)abstract
- Necessary and sufficient conditions for hybrid automata to be non-blocking and deterministic (local existence and uniqueness of executions, respectively) are, developed. The problem of global existence of executions is discussed in the context of Zeno hybrid automata, that is, hybrid automata that exhibit infinitely many discrete transitions in finite time
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| 8. |
- Ohlsson, Henrik, et al.
(författare)
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Blind Identification via Lifting
- 2014
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Ingår i: IFAC PAPERSONLINE. - : ELSEVIER SCIENCE BV. ; , s. 10367-10372
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Konferensbidrag (refereegranskat)abstract
- Blind system identification is known to be an ill-posed problem and without further assumptions, no unique solution is at hand. In this contribution, we are concerned with the task of identifying an ARX model from only output measurements. We phrase this as a constrained rank minimization problem and present a relaxed convex formulation to approximate its solution. To make the problem well posed we assume that the sought input lies in some known linear subspace.
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| 9. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
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Compressive Phase Retrieval From Squared Output Measurements Via Semidefinite Programming
- 2012
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Ingår i: Proceedings of the 16th IFAC Symposium on System Identification. - 9783902823069 ; , s. 89-94
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Konferensbidrag (refereegranskat)abstract
- Given a linear system in a real or complex domain, linear regression aims to recover the model parameters from a set of observations. Recent studies in compressive sensing have successfully shown that under certain conditions, a linear program, namely, l1-minimization, guarantees recovery of sparse parameter signals even when the system is underdetermined. In this paper, we consider a more challenging problem: when the phase of the output measurements from a linear system is omitted. Using a lifting technique, we show that even though the phase information is missing, the sparse signal can be recovered exactly by solving a semidefinite program when the sampling rate is sufficiently high. This is an interesting finding since the exact solutions to both sparse signal recovery and phase retrieval are combinatorial. The results extend the type of applications that compressive sensing can be applied to those where only output magnitudes can be observed. We demonstrate the accuracy of the algorithms through extensive simulation and a practical experiment.
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| 10. |
- Ohlsson, Henrik, et al.
(författare)
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Compressive Shift Retrieval
- 2014
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; , s. 4105-4113
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Tidskriftsartikel (refereegranskat)abstract
- The classical shift retrieval problem considers two signals in vector form that are related by a shift. This problem is of great importance in many applications and is typically solved by maximizing the cross-correlation between the two signals. Inspired by compressive sensing, in this paper, we seek to estimate the shift directly from compressed signals. We show that under certain conditions, the shift can be recovered using fewer samples and less computation compared to the classical setup. We also illustrate the concept of superresolution for shift retrieval. Of particular interest is shift estimation from Fourier coefficients. We show that under rather mild conditions only one Fourier coefficient suffices to recover the true shift.
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