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Showing papers by "Paulo Tabuada published in 2008"


Posted Content
TL;DR: A novel technique is presented that abandons the periodicity assumption by using the current state of the plant to decide the next time instant in which the state should be measured, the control law computed, and the actuators updated.
Abstract: Feedback control laws have been traditionally implemented in a periodic fashion on digital hardware. Although periodicity simplifies the analysis of the mismatch between the control design and its digital implementation, it also leads to conservative usage of resources such as CPU utilization in the case of embedded control. We present a novel technique that abandons the periodicity assumption by using the current state of the plant to decide the next time instant in which the state should be measured, the control law computed, and the actuators updated. This technique, termed self-triggered control, is developed for two classes of nonlinear control systems, namely, state-dependent homogeneous systems and polynomial systems. The wide applicability of the proposed results is illustrated in two well known physical examples: a jet engine compressor and the rigid body.

718 citations


Journal ArticleDOI
TL;DR: It is shown that every incrementally globally asymptotically stable nonlinear control system is approximately equivalent (bisimilar) to a symbolic model, and the approximation error is a design parameter in the construction of the symbolic model.

298 citations


Proceedings ArticleDOI
01 Dec 2008
TL;DR: Two novel distributed implementations of event-triggered and self- Triggered policies over sensor/actuator networks are introduced and their performance in terms of energy expenditure is discussed.
Abstract: Event-triggered and self-triggered control have been recently proposed as an alternative to the more traditional periodic execution of control tasks. The possibility of reducing the number of executions while guaranteeing desired levels of performance makes event-triggered and self-triggered control very appealing in the context of sensor/actuator networks. In this setting, reducing the number of times that a feedback control law is executed implies a reduction in transmissions and thus a reduction in energy expenditures. In this paper we introduce two novel distributed implementations of event-triggered and self-triggered policies over sensor/actuator networks and discuss their performance in terms of energy expenditure.

284 citations


Proceedings ArticleDOI
11 Jun 2008
TL;DR: Self-triggered schedules for the execution of control tasks guarantee asymptotic stability under sample-and-hold implementations while drastically reducing processor usage when compared with the more traditional periodic implementations.
Abstract: Digital implementations of feedback laws commonly consider periodic execution of control tasks. In this paper we go beyond the periodic model by developing self-triggered schedules for the execution of control tasks. These schedules guarantee asymptotic stability under sample-and-hold implementations while drastically reducing processor usage when compared with the more traditional periodic implementations. At the technical level the results rely on a homogeneity assumption on the continuous dynamics and extend to the self-triggered framework some of the advantages of event-triggered implementations recently studied by the authors. The results presented in this paper can be seen as an effort towards understanding the real-time scheduling requirements of control tasks.

145 citations


Journal ArticleDOI
TL;DR: The proposed design methodology can be seen as a correct-by-design way of obtaining both the feedback control laws as well as the control software responsible for deciding which law is executed and when.
Abstract: This paper introduces a methodology for the symbolic control of nonlinear systems based on an approximate notion of simulation relation. This notion generalizes existing exact notions of simulation and is completely characterized in terms of known stabilizability concepts. Equipped with this notion we show how, under certain stabilizability assumptions, we can construct finite or symbolic models for nonlinear control systems. Synthesizing controllers for the original control system can then be done by using supervisory control techniques on the finite models and by refining the resulting finite controllers to hybrid controllers enforcing the specification on the original continuous control system. The proposed design methodology can be seen as a correct-by-design way of obtaining both the feedback control laws as well as the control software responsible for deciding which law is executed and when.

133 citations


Journal ArticleDOI
TL;DR: In this article, the controller synthesis problem for bisimulation equivalence in a wide variety of scenarios including discrete-event systems, nonlinear control systems, behavioral systems, hybrid systems and many others is solved.

55 citations


Book ChapterDOI
22 Apr 2008
TL;DR: The main contribution of this paper consists in showing that under standard assumptions ensuring incremental stability of a switched system, it is possible to construct a symbolic model that is approximately bisimilar to the original switched system with a precision that can be chosen a priori.
Abstract: Switched systems constitute an important modeling para- digm faithfully describing many engineering systems in which software interacts with the physical world. Despite considerable progress on stability and stabilization of switched systems, the constant evolution of technology demands that we make similar progress with respect to different, and perhaps more complex, objectives. This paper describes one particular approach to address these different objectives based on the construction of approximately equivalent (bisimilar) symbolic models for a switched system. The main contribution of this paper consists in showing that under standard assumptions ensuring incremental stability of a switched system (i.e. existence of common or multiple Lyapunov functions), it is possible to construct a symbolic model that is approximately bisimilar to the original switched system with a precision that can be chosen a priori. To support the computational merits of the proposed approach we present a realistic example of a boost dc-dc converter and show how to synthesize a switched controller that regulates the output voltage at a desired level.

39 citations


Journal ArticleDOI
TL;DR: The goal of this paper is to consider a more general form of reduction, termed approximate reduction, in order to extend the class of systems that can be reduced, and gives conditions on when a dynamic system can be projected to a lower dimensional space while providing hard bounds on the induced errors.

34 citations


Proceedings ArticleDOI
01 Dec 2008
TL;DR: This paper drops the periodicity assumption in favour of self-triggered strategies for the execution of control laws, which determine the next execution time based on the current state of the plant.
Abstract: Feedback control laws have been traditionally treated as periodic tasks when implemented on digital platforms. However, the growing complexity of systems calls for efficient implementations of control tasks that reduce resource utilization while keeping desired levels of performance. In this paper we drop the periodicity assumption in favour of self-triggered strategies for the execution of control laws. Such strategies determine the next execution time based on the current state of the plant. Under the self-triggered policy, the inter-execution times scale in a predictable manner: a scaling of the state of the plant entails a scaling in the inter-execution times. This property allows us to derive a simple formula for the next execution time guaranteeing performance.We illustrate the proposed techniques on the control of a jet engine compressor.

14 citations


Proceedings ArticleDOI
01 Dec 2008
TL;DR: This paper addresses the construction of symbolic models for nonlinear control systems affected by disturbances and proposes symbolic models that can be effectively constructed and that are approximately bisimilar to incrementally stable non linear control systems, with arbitrarily good accuracy.
Abstract: Symbolic models are abstract descriptions of continuous systems in which symbols represent aggregates of continuous states. In the last few years there has been a growing interest in the use of symbolic models as a tool for analysis and synthesis of complex systems. In fact, symbolic models enable the use of well known algorithms in the context of supervisory control and algorithmic game theory, for controller synthesis. Since the 1990s many researchers faced the problem of identifying classes of dynamical and control systems that admit symbolic models. In this paper we make further progress along this research line by focusing on control systems affected by disturbances. Our main contribution is to show that incrementally globally asymptotically stable nonlinear control systems with disturbances admit symbolic models. When specializing these results to linear systems, we show that these symbolic models can be easily constructed.

4 citations


Posted Content
TL;DR: This paper shows that under standard assumptions ensuring incremental stability of a switched system, it is possible to construct a finite symbolic model that is approximately bisimilar to the original switched system with a precision that can be chosen a priori.
Abstract: Switched systems constitute an important modeling paradigm faithfully describing many engineering systems in which software interacts with the physical world. Despite considerable progress on stability and stabilization of switched systems, the constant evolution of technology demands that we make similar progress with respect to different, and perhaps more complex, objectives. This paper describes one particular approach to address these different objectives based on the construction of approximately equivalent (bisimilar) symbolic models for switched systems. The main contribution of this paper consists in showing that under standard assumptions ensuring incremental stability of a switched system (i.e. existence of a common Lyapunov function, or multiple Lyapunov functions with dwell time), it is possible to construct a finite symbolic model that is approximately bisimilar to the original switched system with a precision that can be chosen a priori. To support the computational merits of the proposed approach, we use symbolic models to synthesize controllers for two examples of switched systems, including the boost DC-DC converter.