Showing papers by "Maria Domenica Di Benedetto published in 2009"

Symbolic models for nonlinear time-delay systems using approximate bisimulations

Abstract: Time-delay systems are an important class of dynamical systems which provide a solid mathematical framework to deal with many application domains of interest ranging from biology, chemical, electrical, and mechanical engineering, to economics. However, the inherent complexity of such systems poses serious difficulties to control design, when control objectives depart from the standard ones investigated in the current literature, e.g. stabilization, regulation, and etc. In this paper we propose one approach to control design, which is based on the construction of symbolic models, where each symbolic state and each symbolic label correspond to an aggregate of continuous states and to an aggregate of input signals in the original system. The use of symbolic models offers a systematic methodology for control design in which constraints coming from software and hardware, interacting with the physical world, can be integrated. The main contribution of this paper is in showing that incrementally input-to-state stable time-delay systems do admit symbolic models that are approximately bisimilar to the original system, with a precision that can be rendered as small as desired. An algorithm is also presented which computes the proposed symbolic models. When the state and input spaces of time-delay systems are bounded, which is the case in many realistic situations, the proposed algorithm is shown to terminate in a finite number of steps.

Wireless Ventilation Control for Large-Scale Systems: the Mining Industrial Case

Abstract: Mining ventilation is an interesting example of a large scale system with high environmental impact where advanced control strategies can bring major improvements. Indeed, one of the first objectives of modern mining industry is to fulfill environmental specifications [1] during the ore extraction and crushing, by optimizing the energy consumption or the production of polluting agents. The mine electric consumption was 4 % of total industrial electric demand in the US in 1994 (6 % in 2007 in South Africa) and 90 % of it was related to motor system energy [2]. Another interesting figure is given in [3] where it is estimated that the savings associated with global control strategies for fluid systems (pumps, fans and compressors) represent approximately 20 % of the total manufacturing motor system energy savings. This motivates the development of new control strategies for large scale aerodynamic processes based on appropriate automation and a global consideration of the system. More specifically, the challenge in this work is focused on the mining ventilation since as much as 50 % or more of the energy consumed by the mining process may go into the ventilation (including heating the air). It is clear that investigating automatic control solutions and minimizing the amount of pumped air to save energy consumption (proportional to the cube of airflow quantity [4]) is of great environmental and industrial interest.

Multihop multi-channel scheduling for wireless control in WirelessHART networks

Abstract: The WirelessHART standard uses TDMA and channel hopping to control access to the network and to coordinate communication between network devices, in order to enhance reliability and to improve the throughput of the network. A problem in utilizing multiple channels is that current devices are usually equipped with a single transceiver. Thus, a node can only transmit or receive on one channel at a time. Moreover, contrary to today's wired control systems, if a single access point is used the communication becomes the bottle neck of the control system. Therefore this paper presents how one may schedule the WirelessHART communication using two access points. Furthermore the paper describes a scheduling algorithm managing a multihop multi-channel networked control system based on the WirelessHART standard. A simulation example of a multihop multi-channel network is also shown, using the fixed packet lost utility of the Matlab/Simulink-based tool TrueTime.

Discrete state observability of hybrid systems

Abstract: SUMMARY We propose a novel definition of observability, motivated by safety critical applications, given with respect to a subset of critical discrete states that model unsafe or unallowed behaviors. For the class of discrete event systems, we address the problem in the setting of formal (regular) languages and propose a novel observability verification algorithm. For the class of switching systems, we characterize the minimal set of extra output information to be provided by the continuous signals in order to satisfy observability conditions, and propose a milder observability notion that allows a bounded delay in state observation. For the class of hidden Markov models, we analyze decidability and complexity of the verification problem. Copyright q 2009 John Wiley & Sons, Ltd.

Observability and observer‐based control of hybrid systems

Abstract: Addressing significant application domains is important to gain further understanding of the implications of hybrid modeling on control algorithms and to evaluate whether using hybrid formalism can be of substantial help in solving complex, real-life, control problems. In many application domains, hybrid controller synthesis problems are addressed by assuming full hybrid state information, although in many realistic situations state measurements are not available. Hence, to make hybrid controller synthesis relevant, the design of hybrid state observers is of fundamental importance. Moreover in many cases, for example, in communication systems or in fault detection, algorithms for state estimation are important by themselves. Observability has been extensively studied both in the continuous and in the discrete state domains. More recently, various researchers investigated observability of hybrid systems. The definitions of observability and the criteria for assessing this property varied depending on the class of systems under consideration and on the knowledge that is assumed at the output. We believe that this Special Issue, dedicated to observability for hybrid systems, is a useful contribution for the control community as it examines a topic that is in continuous evolution and that offers great opportunities for novel research. Six papers have been selected to reflect the most current research activities. The first two papers address discrete-time linear systems that may switch in an unknown and unpredictable way among different modes taken from a finite set (switching systems). The paper by M. Baglietto, G. Battistelli and L. Scardovi tackles the problem of mode observability with unknown but bounded noises affecting both the system and measurement equations. The paper by P. Caravani and E. De Santis presents conditions of stabilizability for switching systems in terms of a new definition of control invariance. These conditions are based on the realization of a discrete observer that allows the reconstruction of the discrete state in certain intervals of the time basis. The paper by M.D. Di Benedetto, S. Di Gennaro and A. D’Innocenzo proposes a novel definition of observability motivated by safety critical applications given with respect to a subset of critical discrete states. These states model unsafe or unallowed behaviors. This definition is adapted for the class of discrete event systems, for the class of switching systems, and for the class of hidden Markov models. A safety control problem for discrete time block-triangular order preserving hybrid automata with imperfect continuous state information is solved in the paper by D. Del Vecchio. A dynamic feedback law is constructed to guarantee that the continuous state is always outside a bad set. The proposed algorithms, which have linear complexity in the number of variables, are applied to a collision avoidance problem arising in the context of intelligent transportation. The last two papers deal with stochastic systems. The paper by S. Battilotti presents an observer design for a class of single-output nonlinear systems with Markov jumps. The Markov jump process interferes with

A symbolic model approach to the digital control of nonlinear time-delay systems

Abstract: In this paper we propose an approach to control design of nonlinear time-delay systems, which is based on the construction of symbolic models, where each symbolic state and each symbolic label correspond to an aggregate of continuous states and to an aggregate of input signals in the original system. The use of symbolic models offers a systematic methodology for control design in which constraints coming from software and hardware, interacting with the physical world, can be integrated. The main contribution of this paper is in showing that incrementally input-to-state stable time-delay systems do admit symbolic models that are approximately bisimilar to the original system, with a precision that can be rendered as small as desired. An algorithm is also presented which computes the proposed symbolic models. When the state and input spaces of time-delay systems are bounded the proposed algorithm is shown to terminate in a finite number of steps.

A symbolic model approach to the digital control of nonlinear time-delay systems

Abstract: In this paper we propose an approach to control design of nonlinear time-delay systems, which is based on the construction of symbolic models, where each symbolic state and each symbolic label correspond to an aggregate of continuous states and to an aggregate of input signals in the original system. The use of symbolic models offers a systematic methodology for control design in which constraints coming from software and hardware, interacting with the physical world, can be integrated. The main contribution of this paper is in showing that incrementally input-to-state stable time-delay systems do admit symbolic models that are approximately bisimilar to the original system, with a precision that can be rendered as small as desired. An algorithm is also presented which computes the proposed symbolic models. When the state and input spaces of time-delay systems are bounded the proposed algorithm is shown to terminate in a finite number of steps.