Nonlinear Sliding Mode Control for Interconnected Systems with Application to Automated Highway Systems

In this paper, a decentralised control strategy based on sliding mode techniques is proposed for a class of nonlinear interconnected systems. Both matched uncertainties in the isolated subsystems and mismatched uncertainties associated with the interconnections are considered. Under mild conditions, sliding mode controllers for each subsystem are designed in a decentralised manner by only employing local information. Conditions are determined which enable information on the interconnections to be employed within the decentralised controller design to reduce conservatism. The developed results are applied to an automated highway system. Simulation results pertaining to a high-speed following system are presented to demonstrate the effectiveness of the approach

A Forward On-The-Fly Approach for Safety and Reachability Controller Synthesis of Timed Systems

RÉSUMÉ Cette thèse s’intéresse à la synthèse de contrôleurs pour des systèmes temps réel (systèmes temporisés). Partant d’un système temps réel modélisé par un réseau de Petri temporel composé de transitions contrôlables et non contrôlables (TPN), le contrôle vise à forcer, en restreignant les intervalles de franchissement des transitions contrôlables, le système à satisfaire les propriétés souhaitées. Nous proposons, dans cette thèse, un algorithme pour synthétiser de tels contrôleurs pour des propriétés de sûreté et d’accessibilité. Cet algorithme, basé sur la méthode de graphe de classes d’états, calcule à la volée les classes d’états atteignables du TPN tout en collectant progressivement les sous-intervalles de tir à éviter, afin de satisfaire les propriétés souhaitées. Avec cet algorithme, il n’est plus nécessaire de calculer les prédécesseurs contrôlables et de partitionner récursivement les classes d’états jusqu’à atteindre un point fixe, comme c’est le cas dans les autres approches basées sur l’exploration, en avant et en arrière, de l’espace des états du système. Nous prouvons formellement la correction de l’algorithme, puis nous montrons que dans la catégorie des contrôleurs basés sur la restriction des intervalles de tir, l’algorithme, proposé dans cette thèse, synthétise un contrôleur optimal (le plus permissif possible). Afin d’atténuer davantage le problème d’explosion combinatoire, nous montrons comment combiner cette approche avec une abstraction par l’inclusion, par union-convexe ou par enveloppe-convexe. Nous montrons également comment exploiter cet algorithme pour générer des contrôleurs décentralisés. Enfin, nous proposons d’appliquer cet algorithme pour contrôler des TPN par des chronomètres. Notre algorithme permet de partitionner les intervalles des transitions en “bons” et “mauvais” sous-intervalles (à éviter). L’idée est d’utiliser des chronomètres pour suspendre les tâches (transitions) durant leurs mauvais sous-intervalles et les activer dans leurs “bons sous-intervalles”. Il s’agit donc de contrôler les réseaux de Petri temporels en associant des chronomètres aux transitions contrôlables, pour obtenir ainsi des réseaux de Petri temporels contrôlés.----------ABSTRACT This thesis deals with controller synthesis for real time systems (timed systems). Given a real time system modeled as a Time Petri Net (TPN) with controllable and uncontrollable transitions, the control aims at forcing the system to satisfy properties of interest, by limiting the firing intervals of controllable transitions. We propose, in this thesis, an algorithm to synthesize such controllers for safety / reachability properties. This algorithm, based on the state class graph method, computes on-the-fly the reachable state classes of the TPN while collecting progressively firing subintervals to be avoided so that the property is satisfied. It does not need to compute controllable predecessors and then split state classes until reaching a fixpoint, as it is the case for other approaches based on backward and forward exploration of state space of the system. We prove formally the correctness of the algorithm and show that, in the category of state dependent controllers based on the restriction of firing intervals, the algorithm proposed in this thesis, synthesizes maximally permissive controllers. In order to attenuate the state explosion problem, we show how to combine efficiently this approach with an abstraction by inclusion, convex union or convex hull. Afterwards, we discuss the compatibility of this method with distributed systems and decentralized controllers. Finally, we apply this algorithm to control TPN with controllable and uncontrollable transitions by stopwatch. In this approach, we find the subintervals violating the given properties and our objective is to suspend the tasks (transitions) during their bad subintervals and to resume them later. The controller is synthesized through the same algorithm already introduced. In this approach, we suggest to control time Petri nets by associating stopwatches to controllable transitions and to achieve a controlled time Petri nets

Verificação de conflito na supervisão de sistemas concorrentes usando abstrações

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.A explosão do espaço de estados associada ao teste para detecção do conflito é um dos principais problemas que impedem a aplicação da Teoria de Controle Supervisório de Sistemas a Eventos Discretos a sistemas industriais reais. O conflito é uma propriedade global dos sistemas concorrentes sendo que, para sua detecção, deve-se verificar não-bloqueio da composição dos subsistemas que estão sendo verificados. Esta tese trata do problema de detecção de conflito de forma eficiente. Neste trabalho, propõe-se um novo teste de não-conflito baseado em abstrações dos supervisores, obtidas pela operação de projeção natural. Apresentam-se dois conjuntos de condições sobre as abstrações para os quais o teste de não-conflito pode ser aplicado, com resultado equivalente àquele do teste sobre os supervisores originais. No primeiro conjunto de condições os eventos compartilhados são mantidos nas abstrações e a projeção deve possuir a propriedade do observador. O segundo conjunto de condições sobre as abstrações leva em conta propriedades estruturais dos supervisores originais para derivar o conjunto de eventos a serem mantidos nas abstrações, além da propriedade do observador sobre a projeção obtida. As duas abordagens podem ser utilizadas em conjunto para obter abstrações possivelmente melhores, de forma a obter maior redução do espaço de estados na verificação de não-conflito. Apresenta-se ainda um algoritmo para verificação da propriedade do observador. Esta propriedade é utilizada exaustivamente nos resultados apresentados e sua verificação torna-se de grande interesse para a aplicação dos resultados obtidos

Property Enforcement for Partially-Observed Discrete-Event Systems

Engineering systems that involve physical elements, such as automobiles, aircraft, or electric power pants, that are controlled by a computational infrastructure that consists of several computers that communicate through a communication network, are called Cyber-Physical Systems. Ever-increasing demands for safety, security, performance, and certi cation of these critical systems put stringent constraints on their design and necessitate the use of formal model-based approaches to synthesize provably-correct feedback controllers. This dissertation aims to tackle these challenges by developing a novel methodology for synthesis of control and sensing strategies for Discrete Event Systems (DES), an important class of cyber-physical systems. First, we develop a uniform approach for synthesizing property enforcing supervisors for a wide class of properties called information-state-based (IS-based) properties. We then consider the enforcement of non-blockingness in addition to IS-based properties. We develop a nite structure called the All Enforcement Structure (AES) that embeds all valid supervisors. Furthermore, we propose novel and general approaches to solve the sensor activation problem for partially-observed DES. We extend our results for the sensor activation problem from the centralized case to the decentralized case. The methodology in the dissertation has the following novel features: (i) it explicitly considers and handles imperfect state information, due to sensor noise, and limited controllability, due to unexpected environmental disturbances; (ii) it is a uniform information-state-based approach that can be applied to a variety of user-speci ed requirements; (iii) it is a formal model-based approach, which results in provably correct solutions; and (iv) the methodology and associated theoretical foundations developed are generic and applicable to many types of networked cyber-physical systems with safety-critical requirements, in particular networked systems such as aircraft electric power systems and intelligent transportation systems.PHDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137097/1/xiangyin_1.pd

Decentralized control of discrete event systems using prioritized composition with exclusion,”

Abstract-We study the decentralized control of discrete event systems with multiple local specifications. Only a subset of events occur at a local site, and a local specification as well as control/observation capabilities of a local supervisor are defined with respect to such local events. The goal of control is to ensure that the executed behavior at each local site is as desired, i.e., there are multiple specifications, one for each site. We show that the control problem for multiple local specifications is different from that of a single global specification, and present a necessary and sufficient condition for the existence of decentralized supervisors for enforcing the given multiple local specifications. The synthesis of decentralized control for enforcing multiple local specifications is also presented. We also specialize our results to the case of concurrent plants (one which is composed of several local subplants), which offers certain computational savings. The results are illustrated through a simple manufacturing system example. Note to Practitioners-For physically distributed systems, only a certain local set of events is available for control and observation to a controller located at that site. The paper studies the design of a group of local controllers, one for each local site, so the behavior at each site is as desired. Existence conditions for a monolithic plant as well as for a plant composed of multiple subplants are obtained. The results can be used to enforce multiple local specifications using the decentralized control strategy presented in the paper. Index Terms-Discrete event systems, supervisory control, multiple local specifications