| 1. |
- Johansson, Karl Henrik, et al.
(author)
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Modeling of hybrid systems
- 2004
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In: Encyclopedia of Life Support Systems (EOLSS), Theme 6.43: Control Systems, Robotics and Automation. - : Unesco.
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Book chapter (peer-reviewed)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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| 2. |
- Kamgarpour, Maryam, et al.
(author)
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Modeling options for demand side participation of thermostatically controlled loads
- 2013
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In: Bulk Power System Dynamics and Control-IX Optimization, Security and Control of the Emerging Power Grid (IREP), 2013 IREP IREP2013. - 9781479901999
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Conference paper (peer-reviewed)abstract
- Residential thermostatically controlled loads (TCLs) have potential for participation in electricity markets. This is because we can control a large group of these loads to achieve aggregate system behavior such as providing frequency reserves while ensuring the control actions are non-disruptive to the end users. A main challenge in controlling aggregations of TCLs is developing dynamical system models that are simple enough for optimization and control, but rich enough to capture the behavior of the loads. In this work, we propose three classes of models that approximate aggregate TCL dynamics. We analyze these models in terms of their accuracy and computational tractability. The models demonstrate a progression from models that help us analyze and predict TCL population behavior to those that help us develop large-scale automatic control strategies. Specifically, we demonstrate how formal methods from computer science and optimal control can be used to derive bounds on model error, guarantees for trajectory tracking, and algorithms for price arbitrage. We find that the accuracy of the analytic results decreases as TCL parameter heterogeneity is introduced. Thus, we motivate further development of analytical tools and modeling approaches to investigate realistic TCL behavior in power systems.
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| 3. |
- Li, Yuchao, et al.
(author)
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Performance Bounds of Model Predictive Control for Unconstrained and Constrained Linear Quadratic Problems and Beyond
- 2023
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Conference paper (peer-reviewed)abstract
- We study unconstrained and constrained linear quadratic problems and investigate the suboptimality of the model predictive control (MPC) method applied to such problems. Considering MPC as an approximate scheme for solving the related fixed point equations, we derive performance bounds for the closed-loop system under MPC. Our analysis, as well as numerical examples, suggests new ways of choosing the terminal cost and terminal constraints, which are not related to the solution of the Riccati equation of the original problem. The resulting method can have a larger feasible region, and cause hardly any loss of performance in terms of the closed-loop cost over an infinite horizon.
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| 4. |
- Lygeros, John, et al.
(author)
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Continuity and invariance in hybrid automata
- 2001
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In: Proceedings of the 40th IEEE Conference on Decision and Control, 2001. - : IEEE. - 0780370619 ; , s. 340-345
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Conference paper (peer-reviewed)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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| 5. |
- Lygeros, John, et al.
(author)
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On the existence of executions of hybrid automata
- 1999
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In: Proceedings of the 38th IEEE Conference on Decision and Control, 1999. - : IEEE. - 0780352505 ; , s. 2249-2254
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Conference paper (peer-reviewed)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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| 6. |
- Maity, Dipankar, et al.
(author)
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Regret-Optimal Cross-Layer Co-Design in Networked Control Systems - Part II: Gauss-Markov Case
- 2023
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In: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 27:11, s. 2879-2883
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Journal article (peer-reviewed)abstract
- In the first part of this two-letter series, we proposed a cross-layer framework for joint optimal Quality-of-Control (QoC) and Quality-of-Service (QoS) co-design for networked control systems. In this second part, we employ this framework to perform optimal co-design for networked control systems comprising multiple Gauss-Markov systems. We analytically derive the joint optimal policies based on the information couplings between the physical and the network layers. A numerical case study illustrates the framework.
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| 7. |
- Mamduhi, Mohammad H., et al.
(author)
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Regret-Optimal Cross-Layer Co-Design in Networked Control Systems - Part I: General Case
- 2023
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In: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 27:11, s. 2874-2878
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Journal article (peer-reviewed)abstract
- Performance of control systems interacting over a shared communication network is tightly coupled with how the network provides services and distributes resources. Novel networking technology such as 5G is capable of providing tailored services for a variety of network demands. Stringent control requirements and their critical performance specification call for online adaptable and control-aware network services. This perspective suggests a co-design of physical and network layers aiming to ensure that the necessary quality-of-service is provided to achieve the desired quality-of-control. An optimal co-design is in general challenging due to cross-layer couplings between the physical and network layers and their layer-specific functionalities. Furthermore, the complexity of the co-design depends on the level of actionable information the layers share with each other. In this Part I of a two-letter series, we present a general co-design of physical operations and service allocation aiming to minimize a social regret measure for networked control systems. We introduce an optimal networked co-design scenario using the regret index as the joint quality-of-control and quality-of-service (QoC-QoS) measure, and discuss the role of cross-layer awareness in the structure of optimization problems. We mainly focus on the finite-horizon case but we briefly present the infinite-horizon case as well. In Part II, we discuss regret-optimal cross-layer policies for Gauss-Markov systems and derive the optimal solutions based on the general problems introduced in Part I.
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| 8. |
- Mattila, Robert
(author)
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Hidden Markov Models: Identification, Inverse Filtering and Applications
- 2020
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Doctoral thesis (other academic/artistic)abstract
- A hidden Markov model (HMM) comprises a state with Markovian dynamics that is hidden in the sense that it can only be observed via a noisy sensor. This thesis considers three themes in relation to HMMs, namely, identification, inverse filtering and applications.In order to employ an HMM, its parameters have first to be identified (or, estimated) from data. Traditional maximum-likelihood estimation procedures may, in practice, suffer from convergence to bad local optima and high computational cost. Recently proposed methods of moments address these shortcomings, but are less accurate. We explore how such methods can be extended to incorporate non-consecutive correlations in data so as to improve their accuracy (while still retaining their attractive properties).Motivated by applications in the design of counter-adversarial autonomous (CAA) systems, we then ask the question: Is it possible to estimate the parameters of an HMM from other data sources than just raw measurements from its sensor? To answer this question, we consider a number of inverse filtering problems. First, we demonstrate how HMM parameters and sensor measurements can be reconstructed from posterior distributions from an HMM filter. Next, we show how to estimate such posterior distributions from actions taken by a rational agent. Finally, we bridge our results to provide a solution to the CAA problem of remotely estimating the accuracy of an adversary’s sensor based on its actions.Throughout the thesis, we motivate our results with applications in various domains. A real-world application that we investigate in particular detail is how the treatment of abdominal aortic aneurysms can be modeled in the Markovian framework. Our findings suggest that the structural properties of the optimal treatment policy are different than those recommended by current clinical guidelines – in particular, that younger patients could benefit from earlier surgery. This indicates an opportunity for improved care of patients with the disease.
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| 9. |
- Nordlund, Per-Johan, 1971-
(author)
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Efficient Estimation and Detection Methods for Airborne Applications
- 2009
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Doctoral thesis (other academic/artistic)abstract
- The overall purpose with this thesis is to investigate and provide computationally efficient methods for estimation and detection. The focus is on airborne applications, and we seek estimation and detection methods which are accurate and reliable yet effective with respect to computational load. In particular, the methods shall be optimized for terrain-aided navigation andcollision avoidance respectively. The estimation part focuses on particle filtering and the in general much more efficient marginalized particle filter. The detection part focuses on finding efficient methods for evaluating the probability of extreme values. This is achieved by considering the, in general, much easier task to compute the probability of level-crossings.The concept of aircraft navigation using terrain height information is attractive because of the independence of external information sources. Typicallyterrain-aided navigation consists of an inertial navigation unit supported by position estimates from a terrain-aided positioning (TAP) system. TAP integrated with an inertial navigation system is challenging due to its highly nonlinear nature. Today, the particle filter is an accepted method for estimation of more or less nonlinear systems. At least when the requirements on computational load are not rigorous. In many on-line processing applications the requirements are such that they prevent the use of theparticle filter. We need more efficient estimation methods to overcome this issue, and the marginalized particle filter constitutes a possible solution. The basic principle for the marginalized particle filter is to utilize linear and discrete substructures within the overall nonlinear system. These substructures are used for efficient estimation by applying optimal filters such as the Kalman filter. The computationally demanding particle filter can then be concentrated on a smaller part of the estimation problem.The concept of an aircraft collision avoidance system is to assist or ultimately replace the pilot in order to to minimize the resulting collision risk. Detection is needed in aircraft collision avoidance because of the stochastic nature of thesensor readings, here we use information from video cameras. Conflict is declared if the minimum distance between two aircraft is less than a level. The level is given by the radius of a safety sphere surrounding the aircraft.We use the fact that the probability of conflict, for the process studied here, is identical to the probability for a down-crossing of the surface of the sphere. In general, it is easier to compute the probability of down-crossings compared to extremes. The Monte Carlo method provides a way forward to compute the probability of conflict. However, to provide a computationally tractable solution we approximate the crossing of the safety sphere with the crossing of a circular disc. The approximate method yields a result which is as accurate as the Monte Carlo method but the computational load is decreased significantly.
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| 10. |
- Simic, Slobodan, et al.
(author)
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Hybrid limit cycles and hybrid Poincaré-Bendixson
- 2002
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In: Proceedings of the 15th IFAC World Congress, 2002. - : IFAC.
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Conference paper (peer-reviewed)abstract
- We present two results about regular hybrid systems with no branching (Simić et al., 2000a). The first one provides a condition for asymptotic stability of hybrid closed orbits in terms of contraction-expansion rates of resets and flows in a hybrid system. The second one is a generalization of the Poincaré-Bendixson theorem to planar hybrid systems.
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