Xenofon D. Koutsoukos

Supervisory control of hybrid systems

In this paper, the supervisory control of hybrid systems is introduced and discussed at length. Such control systems typically arise in the computer control of continuous processes, for example, in manufacturing and chemical processes, in transportation systems, and in communication networks. A functional architecture of hybrid control systems consisting of a continuous plant, a discrete-event controller, and an interface is used to introduce and describe analysis and synthesis concepts and approaches. Our approach highlights the interaction between the continuous and discrete dynamics, which is the cornerstone of any hybrid system study. Discrete abstractions are used to approximate the continuous plant. Properties of the discrete abstractions to be appropriate representations of the continuous plant are presented, and important concepts such as determinism and controllability are discussed. Supervisory control design methodologies are presented to satisfy control specifications described by formal languages. Several examples are used throughout the paper to illustrate our approach.

Timed Petri Nets in Hybrid Systems: Stability and SupervisoryControl

In this paper, timed Petri nets are used to model and control hybrid systems. Petri nets are used instead of finite automata primarily because of the advantages they offer in dealing with concurrency and complexity issues. A brief overview of existing results on hybrid systems that are based on Petri nets is first presented. A class of timed Petri nets named programmable timed Petri nets (PTPN) is then used to model hybrid systems. Using the PTPN, the stability and supervisory control of hybrid systems are addressed and efficient algorithms are introduced. In particular, we present sufficient conditions for the uniform ultimate boundness of hybrid systems composed of multiple linear time invariant plants which are switched between using a logical rule described by a Petri net. This paper also examines the supervisory control of a hybrid system in which the continuous state is transfered to a region of the state space in a way that respects safety specifications on the plants discrete and continuous dynamics.

Fault modeling for monitoring and diagnosis of sensor-rich hybrid systems

This paper presents a framework for modeling faults in hybrid systems that leads to an efficient approach for monitoring and diagnosis of real-time embedded systems. We describe a fault parameterization based on hybrid automata models and consider both abrupt failures and gradual degradation of system components. Our approach also addresses the computational problem of coping with large amount of sensor data by using a discrete event model of the system so as to focus distributed signal analysis on when and where to look for signatures of interest. The approach has been demonstrated for the online diagnosis of a hybrid system, the Xerox DC265 printer.

Sensing field: coverage characterization in distributed sensor networks

The ability to characterize sensing quality is central to the design and deployment of practical distributed sensor networks. This paper introduces the concept of a sensing field defining, for each point in the physical space of a phenomenon of interest, a measure of how well a sensor network can sense the phenomenon at that point. Using target localization and tracking as examples, the paper derives an upper bound for this measure of goodness measure, using the Cramer-Rao bound and models of sensor observation and network layout. It then evaluates the validity of statistical observation models used by a family of estimators. Simulation results of applying the analytical analysis to a randomly spaced network are presented.

Design of hybrid system regulators

In this paper, a new approach for modeling and controlling hybrid systems is presented. Discrete abstractions are used to approximate the continuous dynamics and emphasis is placed on the nondeterministic nature of the abstracting models. The regulator problem for hybrid systems is formulated and an example of a robotic manufacturing system is used to illustrate the approach.

HIERARCHICAL CONTROL FOR A CLASS OF UNCERTAIN PIECEWISE LINEAR HYBRID DYNAMICAL SYSTEMS

Abstract In this paper, we consider the hierarchical control problem for a class of uncertain hybrid dynamical systems. The continuous dynamics of this class of uncertain hybrid systems are described by linear difference state equations, whose right side functions are unknown but lie within some convex hulls of known functions. Our control objective is for the closed loop system to exhibit a desired behavior under the dynamic uncertainty, continuous disturbances and uncontrollable events. One of the main questions is the existence of appropriate controllers. We will focus on this question here, and present a novel methodology for the analysis of uncertain piecewise linear hybrid dynamical systems (PLHDS) based on backward reachability analysis. For this purpose, we derive the predecessor operator for this class of uncertain PLHDS. Then both static control specifications such as safety and reachability, and dynamic control specifications are considered. A temperature control system is used for illustration.

Characterization of Stabilizing Switching Sequences in Switched Linear Systems Using Piecewise Linear Lyapunov Functions

In this paper, the stability of switched linear systems is investigated using piecewise linear Lyapunov functions. Given a switched linear system, we present a systematic methodology for computing switching laws that guarantee stability based on the matrices of the system. We assume that each individual subsystem is stable and admits a piece-wise linear Lyapunov function. Based on these Lyapunov functions, we compose global Lyapunov functions that guarantee stability of the switched linear system. A large class of stabilizing switching sequences for switched linear systems is characterized by computing conic partitions of the state space. The approach is applied to both discrete-time and continuous-time switched linear systems.

Hybrid Control Systems Usind Timed Petri Nets: Supervisory Control Design Based on Invariant Properties

In this paper, a class of timed petri nets named programmable timed petri nets is used for supervisory control of hybird system. In particular, the transfer of the continuous state to a region of the state space under safety specifications on the discrete and continuous dynamics is addressed. The switching policy is embedded in the dynamics of the underlying Petri net structure and the supervisors are described by Petri nets. The discrete specific ations are expressed in terms of linear constraints on the marking vector and are satisfied by applying supervisory control of Petri nets based on place invariants. The hybrid system switches from a subsystem to another, in a way that the state gradually progresses from one equilibrium to another towards the desired target equilibrium. The supervisory control algorithm is designed to allow switchings to occur only on the intersection of the invariant manifolds. Finally, in the case when the continuous dynamics are described by first order integrators, the design algorithm is formulated as a linear programming problem.

CHAPTER 3 – Computational Issues in Intelligent Control: Discrete-Event and Hybrid Systems

Intelligent control methodologies are being developed to address the control needs of complex systems that exhibit complicated dynamical behaviors. The design, simulation, and verification of intelligent control systems is highly nontrivial and typically involves significant amount of computations. In this paper, we identify and discuss several computational issues that are central in intelligent control. In particular, we discuss how the design, simulation, and verification of discrete-event and hybrid systems, which are central in intelligent control, requires the development of computationally efficient algorithms and approaches. Petri net models are used to describe discrete event and hybrid systems. Computational issues of various problems and algorithms concerning the analysis and synthesis of such systems are discussed. In view of hybrid systems, we also review basic computational issues for hybrid automata. Finally, we present a parallel computing architecture for intelligent control systems and we illustrate its advantages by considering parallel discrete event simulations.

A Hybrid Feedback Regulator Approach to Control an Automotive Suspension System

In this paper, we demonstrate a novel hybrid control synthesis approach using an automotive suspension system. Discrete abstractions are used to approximate the continuous dynamics and emphasis is placed on the nondeterministic nature of the abstracting models. The regulator problem for hybrid systems is formulated for safety specifications and algorithms for control design are presented.