Resource Management for Control Tasks Based on the Transient Dynamics of Closed-Loop Systems

This paper presents a resource management strategy for control tasks that maximizes control performance within the available resources by readjusting the task periods at run-time. A feedback scheduler is used to determine on-line the optimal task periods considering the response over a finite time horizon of the plants controlled by arbitrary linear control laws. We show how this problem can be expressed as an optimization problem, where the objective function relates the sampling periods to the transient responses of the controlled plants, and where restrictions are based on EDF schedulability constraints. For the general case, the solution of the optimization problem is computationally expensive, and thus, an approximate procedure to be executed on-line has been developed. We present simulation results that validate the presented approach

Fuzzy Feedback Scheduling of Resource-Constrained Embedded Control Systems

The quality of control (QoC) of a resource-constrained embedded control system may be jeopardized in dynamic environments with variable workload. This gives rise to the increasing demand of co-design of control and scheduling. To deal with uncertainties in resource availability, a fuzzy feedback scheduling (FFS) scheme is proposed in this paper. Within the framework of feedback scheduling, the sampling periods of control loops are dynamically adjusted using the fuzzy control technique. The feedback scheduler provides QoC guarantees in dynamic environments through maintaining the CPU utilization at a desired level. The framework and design methodology of the proposed FFS scheme are described in detail. A simplified mobile robot target tracking system is investigated as a case study to demonstrate the effectiveness of the proposed FFS scheme. The scheme is independent of task execution times, robust to measurement noises, and easy to implement, while incurring only a small overhead.Comment: To appear in International Journal of Innovative Computing, Information and Contro

Neural Feedback Scheduling of Real-Time Control Tasks

Many embedded real-time control systems suffer from resource constraints and dynamic workload variations. Although optimal feedback scheduling schemes are in principle capable of maximizing the overall control performance of multitasking control systems, most of them induce excessively large computational overheads associated with the mathematical optimization routines involved and hence are not directly applicable to practical systems. To optimize the overall control performance while minimizing the overhead of feedback scheduling, this paper proposes an efficient feedback scheduling scheme based on feedforward neural networks. Using the optimal solutions obtained offline by mathematical optimization methods, a back-propagation (BP) neural network is designed to adapt online the sampling periods of concurrent control tasks with respect to changes in computing resource availability. Numerical simulation results show that the proposed scheme can reduce the computational overhead significantly while delivering almost the same overall control performance as compared to optimal feedback scheduling.Comment: To appear in International Journal of Innovative Computing, Information and Contro

Design of Stable Feedback Controllers for Second Order Systems with Varying Sampling Rate: LQ and Lie-Algebraic Approaches

Abstract: In this article, we consider the design of a controller family that given a second-order continuous-time linear plant controlled at a varying rate, asymptotically stabilizes the closed loop and provides a good performance. Rate adaptation of control task execution is increasingly used in order to optimize allocation and throughput of shared resources in embedded systems. The LQ technique, tipically used to adapt the controller parameters to rate variation, is compared with a Lie-algebraic method [7] which guarantees the existence of a common Lyapunov function for the varying-time system. The use of a performance index as a function of the rate, derived from the discrete Lyapunov function and related with closed-loop eigenvalues, simplifies the evaluation of the cost associated with each rate

An approach for stability analysis of systems with varying sampling rate

In dieser Arbeit wird ein Verfahren zur Stabilitätsprüfung hybrider Systeme beschrieben. Das entwickelte Verfahren lässt es zu, einen garantiert stabilen Bereich für die Variation der Abtastzeit anzugeben. Da veränderliche Abtastzeiten äquivalent zu variierenden Laufzeiten sind, wie sie beispielsweise durch Bussysteme verursacht werden, kann das Verfahren auch auf dezentrale hybride Regelungen angewendet werden, bei denen Sensoren und Aktoren über Bussysteme mit der Regelung gekoppelt sind. Die zur Herleitung des Verfahrens eingesetzten Methoden basieren auf dem Begriff der robusten Stabilität, die es ermöglicht, Stabilität für Systeme zu garantieren, die Unsicherheiten unterliegen. Daher wird die veränderliche Abtastzeit in einem ersten Schritt durch einen nichtlinearen Eingriff modelliert und anschließend in eine äquivalente Unsicherheit umgerechnet. Die Darstellung des mit Unsicherheiten behafteten Systems erfolgt als lineare Fraktionaltransformation. Anhand dieses Modells wird anschließend die Stabilität in Bezug auf eine Variation der Abtastzeit untersucht. Als Ergebnis des Verfahrens erhält man einen Bereich für die Abtastzeit, in dem Stabilität für das Gesamtsystem garantiert werden kann. Dabei ist es unerheblich, mit welcher Dynamik die Abtastzeit verändert wird. Anschließend werden die theoretischen Ergebnisse anhand eines realen Systems verifiziert. Dazu wurde im Rahmen eines Industrieprojektes ein Versuchsstand mit vier auf Winkelgleichlauf zu regelnden Gleichstromantrieben aufgebaut, eine Regelung entworfen und diese in eine speicherprogrammierbare Steuerung implementiert. Die Kommunikation der Regelung mit den Stellgliedern und der Messwerterfassung erfolgte über ein Bussystem. Nach der Modellierung des Gesamtsystems wird mit Hilfe des entwickelten Verfahrens der garantiert stabile Bereich für die Variationsbreite der Abtastzeit am Versuchsstand berechnet und die so bestimmten Stabilitätsgrenzen durch Messungen am Prüfstand verifiziert.In this thesis, a method is presented which allows the specification of stability margins for hybrid control systems composed of a sampled data feedback controller with varying sampling time and a continous linear system. The developed method provides lower und upper bounds for the sampling time and thus defining a range within guaranteed stability is ensured. The effect of varying sampling time and varying time delays of bus systems are equivalent. Therefore, the presented method can also be used for stability tests of decentralized controlled hybrid systems where the sensors and the actuators are linked to the controller by various bus systems. The derivation of the method is based on concepts of robust stability, which allows stability tests for systems with uncertainties. In a first step the varying sampling time is modeled by a non-linear operation. Afterwards, the non-linearity is converted into an uncertainty. Now the system can be represented as a linear fractional transformation. Based on this model the stability of the time varying system can be analyzed with respect to variations of sampling time. As a result this method specifies a range for the sampling time within which stability of the varying system can be guaranteed, regardless of the dynamics of the variation. Afterwards, the theoretical results are verified by measurements on a real system. A test bed was set up within the frame of an industrial project. The controllers were implemented in a programmable logic controller to ensure position synchronisation of four DC motors. All communications between the controller, actuators and sensors are established by bus systems. After modeling the overall system, the presented method is used to determine the stability margins of the test bed concerning the sampling time. Finally, the calculated bounds are verified by measurements

Optimal Bandwidth Allocation and Control for Networked Control Systems with Disturbance and Noise

A networked control system (NCS) is an interconnected control system in which sensors, actuators, and controllers communicate with each other through a shared network. Although NCSs are beneficial thanks to easy maintenance, architectural flexibility, decreased wiring weights, and tele-operating possibilities, NCSs also have some challenges such as disturbance, noise, bandwidth limitation, delay, and packet dropout. The popularization of smartphones and the drastically increasing number of internet of things (IoT) devices require not only a high-speed internet such as 5G, but also a wise strategy for optimal bandwidth allocation. In this dissertation, optimal bandwidth allocations for NCSs with disturbance and noise are proposed based on performance index function (PIF), artificial neural network (ANN), and Q-learning algorithms. A ball magnetic-levitation (maglev) system, four DC motor speed-control systems, and a wireless autonomous robotic wheelchair are implemented as test beds. The relationship between system performance, sampling frequency, and the standard deviation of white Gaussian disturbance are approximated using a 6 th-degree polynomial. The PIF and ANN methods can estimate the standard deviation of disturbance when current a sampling frequency and an error variance are provided. Dynamic bandwidth allocation using PIF, ANN, and Q-learning is proposed and verified by experimental results for a single-server and single-client DC motor system. The proposed methods show integral absolute errors (IAE) of 166 615, 16 773, and 16 945 and bandwidth utilizations (BU) of each method are 13.15%, 13.38%, and 13.98%, respectively, after 15 000 iterations, when various standard deviations of disturbance are injected. These results present a better performance and a reasonable average BU compared to fixed sampling frequencies. When information of the estimated standard deviation of disturbance, BU margin of safety, weight of each system, and total time delay is given, the optimal sampling frequency for a multi-server and multi-client system can be determined based on the PIF, ANN, and Q-learning, respectively. They are validated by experiments in two cases. The first case is conducted with a ±0.8-V disturbance, 10% safety margin of BU, 1.25-ms total time delay, and various weights for four DC motor systems. The second has the conditions of a ±0.8-V disturbance, 10% safety margin of BU, 1.25-ms total time delay, various weights for four DC motor systems with a maglev and a wheelchair robot system, of which BUs are 44% and 1% respectively. Experimental results prove that all three methods can be used to find the optimal sampling frequencies for each system when an NCS has limited bandwidth as well as sufficient bandwidth

Réseaux de communication et applications de contrôle-commande

Cette thèse se situe dans le domaine des Systèmes Commandés en Réseaux, systèmes pluridisciplinairesqui connaissent un grand développement dans le contexte technologique actuel etqui introduisent de nouveaux problèmes de recherche, en particulier, pour les communautés Automatiqueet Réseau de Communication. L objectif est de montrer l intérêt de considérer un lienbidirectionnel entre la Qualité de Contrôle (QdC) (stabilité et performance des applications decontrôle-commande) et la Qualité de Service (QdS) (retards dans les transmissions) en se focalisantsur les réseaux locaux et plus particulièrement sur l ordonnancement des trames dans la souscouche MAC où on considère des protocoles MAC de type CSMA.Notre travail se situe tout d abord dans le cadre du réseau CAN où nous faisons trois propositions.La première proposition consiste en des solutions de QdS pour des applications decontrôle-commande sur la base du concept de priorité hybride, pour l ordonnancement de trames,dans laquelle nous définissons une partie priorité dynamique qui dépend d un paramètre de QdC.Ceci permet de réaliser une relation QdC->QdS. La deuxième proposition consiste en des solutionsde QdC par une méthode de compensation de retard (maintenance des pôles dominants)ce qui permet de réaliser une relation QdS->QdC. La troisième proposition consiste à réaliserune relation QdC QdS qui assure lors de l implantation de plusieurs applications, une propriétéd équité comportementale. Nous abordons ensuite le cadre particulier des réseaux locaux sans filoù, d une part, nous définissons des protocoles MAC de type CSMA sans collision sur la basede priorités et, d autre part, nous montrons la faisabilité des idées développées dans le cadre duréseau CANThis thesis is in the field of Networked Controlled Systems, which are multidisciplinary systemsand which experience a great development in the context of the current technology andintroduce new research problems, particularly for the communities of Automatic Control andCommunication Network. The aim is to show the interest in considering a bidirectional link betweenthe Quality of Control (QoC) (stability and performance of process control applications) andQuality of Service (QoS) (delays in the transmissions) and to focus on Local Area Networks and,more particularly, on the scheduling of frames in the MAC layer in which we consider CSMAMAC protocols.Our work first concerns a CAN network where we have three proposals. The first proposalconsists of solutions for QoS, for process control applications, which are based on the conceptof hybrid priority for the frame scheduling in which we define a dynamic priority part which dependson a QoC parameter. This allows to implement a relation QoC->QoS. The second proposalconsists of QoC solutions by using a compensation method for time delays (maintenance of dominantpoles) which allows to implement a relation QoS->QoC. The third proposal consists inimplementing a relation QoS QoC that ensures, for the implementation of several applications,a fairness property. We then discuss the specific context of Wireless LANs, where, on the onehand, we define collision-free CSMA MAC protocols on the basis of priorities and, on the otherhand, we show the feasibility of the ideas developed in the CAN networkTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Algoritmos de controlo distribuído em sistemas baseados em microprocessadores

Doutoramento em Engenharia ElectrónicaO trabalho de investigação apresentado nesta tese trata dos problemas associados à distribuição de controladores digitais em sistemas baseados em microprocessadores. A utilização deste tipo de sistemas tornou-se comum ao longo da última década em domínios como a automação industrial, o controlo de processos, a robótica, a domótica, assim como na indústria automóvel e aeronáutica. A distribuição de uma malha de controlo faz-se recorrendo a nós fisicamente distintos para a implementação do sensor, do controlador e do actuador, ligados entre si através de uma rede de comunicação. Na maior parte dos sistemas embutidos distribuídos actuais a rede de comunicação e os processadores locais de cada nó são utilizados por vários tipos de aplicações tanto de tempo-real como de outro tipo. Os sistemas de controlo distribuído implementados deste modo apresentam características próprias que diferem das que caracterizam os sistemas de controlo centralizado. Uma dessas características é a existência de um atraso variável entre o momento da amostragem e o momento da actuação. Este tipo de atrasos provoca a degradação do desempenho de controlo, podendo mesmo em alguns casos conduzir à perda de estabilidade da malha de controlo. Neste trabalho propõem-se técnicas de controlo lineares e não-lineares para melhorar o desempenho de controlo neste tipo de sistemas embutidos. As técnicas propostas são validadas através da simulação de vários sistemas utilizando um simulador para sistemas de tempo-real baseado em MATLAB/Simulink.This thesis proposes solutions to the problems that arise with the distribution of control systems in systems based in microprocessors. The use of this kind of systems grew over the past decade in areas like industrial automation, process control, robotics, building automation and the automobile and aeronautical industries. The distribution of a control loop consists in the placement of the sensor, the controller and the actuator in different nodes, connected though a communication network. In modern embedded distributed systems both the communication network and the local processors are used by several real-time and non real-time applications. This kind of implementations of the distributed controllers presents characteristics that are different from the ones of centralized controllers. They usually present variable delay between the sampling and the actuation instants. These delays degrade the performance of the controller and can even destabilize the control loops. In this thesis linear and non-linear control techniques are proposed to improve the control performance of such embedded control systems. The proposed techniques are validated by the simulation of different plants using a real-time systems simulator based on MATLAB/Simulink.10117230