35 research outputs found
The Wireless Control Bus: Enabling Efficient Multi-Hop Event-Triggered Control with Concurrent Transmissions
No full textEvent-triggered control (ETC) holds the potential to significantly improve the efficiency of wireless networked control systems. Unfortunately, its real-world impact has hitherto been hampered by the lack of a network stack able to transfer its benefits from theory to practice specifically by supporting the latency and reliability requirements of the aperiodic communication ETC induces. This is precisely the contribution of this article.Our Wireless Control Bus (WCB) exploits carefully orchestrated network-wide floods of concurrent transmissions to minimize overhead during quiescent, steady-state periods, and ensures timely and reliable collection of sensor readings and dissemination of actuation commands when an ETC triggering condition is violated. Using a cyber-physical testbed emulating a water distribution system controlled over a real-world multi-hop wireless network, we show that ETC over WCB achieves the same quality of periodic control at a fraction of the energy costs, therefore unleashing and concretely demonstrating its full potential for the first time.Team Manuel Mazo J
Towards Traffic Bisimulation of Linear Periodic Event-Triggered Controllers
No full textWe provide a method to construct finite abstractions exactly bisimilar to linear systems under a modified periodic event-triggered control (PETC), when considering as output the inter-event times they generate. Assuming that the initial state lies on a known compact set, these finite-state models can exactly predict all sequences of sampling times until a specified Lyapunov sublevel set is reached. Based on these results, we provide a way to build tight models simulating the traffic of conventional PETC. These models allow computing tight bounds of the PETC average frequency and global exponential stability (GES) decay rate. Our results are demonstrated through a numerical case study.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Tamas Keviczk
Self-triggered output-feedback control of LTI systems subject to disturbances and noise
No full textSelf-triggered control (STC) and periodic event-triggered control (PETC) are aperiodic sampling techniques aiming at reducing control data communication when compared to periodic sampling. In both techniques, the effects of measurement noise in continuous-time systems with output feedback are unaddressed. In this work we prove that additive noise does not hinder stability of output-feedback PETC of linear time-invariant (LTI) systems. Then we build an STC strategy that estimates PETC's worst-case triggering times. To accomplish this, we use set-based methods, more specifically ellipsoidal sets, which describe uncertainties on state, disturbances and noise. Ellipsoidal reachability is then used to predict worst-case triggering condition violations, ultimately determining the next communication time. The ellipsoidal state estimate is recursively updated using guaranteed state estimation (GSE) methods. The proposed STC is designed to be computationally tractable at the expense of some added conservatism. It is expected to be a practical STC implementation for a broad range of applications.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Tamas Keviczk
En el terreno de las paradojas: nacionalismo, identidad étnica e ideología en América Latina
No full textThe author analyzes the political space that nationalism of the XIX th century, revolutionary nationalism, Marxism, and democratizing project), the author examines trends observed over time. These constants encapsulate the difficulties, also known as paradoxes, to formulate an integrated project in which belonging to a Nation, and conserving one's ethnic identity are not irreconcilable differences.La autora analiza el lugar que la ideología nacionalista, en sus distintas versiones históricas, ha otorgado a los grupos indígenas. Alrededor de cuatro ejes representativos (el nacionalismo liberal del siglo XIX, el nacionalismo revolucionario, el marxismo y el proyecto democratizador), la autora enfatiza en las constantes que se observan a lo largo del tiempo, pues son éstas las que expresan las dificultades -frecuentemente planteadas como paradojas- para formular un proyecto integrador en el cual la plena pertenencia a la comunidad nacional y la conservación de identidades étnicas no son alternativas irreconciliables
Engineering carbon fixation in E. coli : from heterologous RuBisCO expression to the Calvin–Benson–Bassham cycle
No full textSelf-Triggered Control for Near-Maximal Average Inter-Sample Time
No full textSelf-triggered control (STC) is a sample-and-hold control method aimed at reducing communications in networked-control systems; however, existing STC mechanisms often maximize how late the next sample is, thus not optimizing sampling performance in the long-term. In this work, we devise a method to construct self-triggered policies that provide near-maximal average inter-sample time (AIST) while respecting given control performance constraints. To achieve this, we rely on finite-state abstractions of a reference event-triggered control, while also allowing earlier samples. These early triggers constitute controllable actions of the abstraction, for which an AIST-maximizing strategy can be obtained by solving a mean-payoff game. We provide optimality bounds, and how to further improve them through abstraction refinement techniques.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Manuel Mazo J
Periodic event-triggered control with a relaxed triggering condition
No full textIn networked control systems (NCSs), extensive data exchange between plants and controllers leads to an unnecessary usage of communication and computational resources. Aperiodic sample-and-hold methods such as event-triggered control (ETC) can reduce the number of transmissions, allowing more applications to operate within the same network. However, most existing event-triggering mechanisms enforce a Lyapunov function of the continuous-time closed-loop system to be (almost) always decreasing. We propose a relaxed triggering condition for periodic event-triggered control (PETC) based on bounding the Lyapunov function with an exponentially decaying reference function, which reduces the communications while guaranteeing the same decay rate as competing strategies. We provide sufficient global exponential and input-to-state stability conditions for linear time-invariant (LTI) systems under our event-based state feedback, giving explicit performance guarantees in the presence of additive disturbances. Finally, some simulation results illustrate the performance of the proposed control strategy.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Tamas Keviczk
Timing is everything: Analysis and synthesis of traffic patterns in event-triggered control
No full textEvent-triggered control (ETC) and self-triggered control (STC) are sample-and-hold control paradigms in which sensor data is only updated to the controller when necessary, often aperiodically, in contrast to the well-established periodic sampling paradigm. In ETC, a state-dependent event triggers a transmission, while in STC the controller decides when to request the next sample. The main objective of ETC and STC is to reduce sampling and transmissions when either sampling/transmitting is costly or network resources are scarce. However, despite years of development in the ETC/STC field, little is known about their sampling performances or how to accommodate the generated aperiodic traffic of multiple ETC systems in a shared communication medium. This dissertation presents methods to (i) schedule multiple ETC systems in a shared network, (ii) evaluate ETC systems' sampling performance, and (iii) creating STC strategies that improve ETC systems' sampling performance. In particular, we focus for the most part on ETC applied to linear time-invariant (LTI) systems. To solve these problems, we first model the timing behavior of ETC/STC systems, obtaining what we call traffic models. The states of a traffic model are the transmitted samples and its output is the elapsed time between consecutive transmissions, the inter-sample time (IST). These models are infinite-state systems that can exhibit very complex—even chaotic—behavior, as we demonstrate. To solve synthesis problems such as scheduling and optimal STC sampling strategies, we augment the models with early-sampling choices, which are guaranteed to preserve control stability and performance. The models are then abstracted into finite-state systems or timed automata, on which many of our problems can be computationally solved. Using these abstractions, the obtained schedulers are always valid for the real systems, and the obtained metrics are always formal bounds to the real system's performance. Our abstraction method is based on quotient and l-complete systems. That is, we partition the state-space into regions, each region comprising all states whose next IST, or next sequence of l ISTs, is the same. This is made possible by observing that periodic ETC (PETC)—a practical version of ETC where events are checked periodically—has a finite output set, and that each obtained region is described by an intersection of finitely many quadratic cones. The abstraction transitions, which enable predicting how samples and their corresponding ISTs evolve over time, can be computed exactly using nonlinear satisfiability-modulo-theories solvers, or approximately through convex semi-definite relaxations. Infinite periodic IST patterns arising from these abstractions can be verified to exist in the real traffic model via an eigenvector problem, which is central for solving problem (ii) exactly. Our methodology comprises a comprehensive framework for solving qualitative (scheduling) and quantitative (sampling performance) problems for ETC and STC, as well as a computational machinery that automates these processes, ultimately consolidated in the open-source tool ETCetera. With the developed methods, we can show cases where ETC significantly outperforms periodic sampling in terms of average inter-sample time, and how to increase this performance further using look-ahead. We also manage to solve the ETC scheduling problem efficiently, which is helped by an abstraction minimization algorithm that we propose. In summary, this dissertation provides new tools to understand and manipulate ETC traffic, and ultimately casts new light on the practical relevance of ETC and STC.Team Manuel Mazo J
Periodic event-triggered control for congested networked control systems
No full textWith the recent development of control systems, event-triggered control (ETC) has been introduced to prevent unnecessary usage of resources, which often happens under time-based control implementations. This thesis presents a novel approach to periodic event-triggered control (PETC) that aims at reducing the number of transmissions between the controller and the sensors even further. This goal is particularly important in networked control systems (NCSs), where communication and computation resources are scarce. In this report, a relaxed triggering condition is introduced that relies on bounding the Lyapunov function of the continuous-time closed-loop system with an exponentially decaying function, rather than requiring its monotone decrease. The relaxed PETC achieves significantly less transmissions compared to existing PETC implementations. The thesis pushes the limit of event-triggeredcontrol even further, by introducing an algorithm for a scheduler of NCS that allows to skip some of the events. This can be seen as a ‘last resort’ approach, that postpones the transmission as much as possible. It is inspired by methods used in self-triggered control (STC) and scheduling event-based NCS. Reducing the communication between the plant and the controller introduces some trade-offs that are also discussed in this report. Finally, several modifications of presented ideas are given that can be applied depending on the main objectiveson the performance of the control loop.Mechanical Engineering | Systems and Contro
Self-triggered output feedback control for perturbed linear systems
No full textIn this work we propose a Self-Triggered Control (STC) strategy for linear time-invariant (LTI) systems subject to bounded disturbances, using LTI discrete-time dynamic output-feedback. The STC logic computes worst-case triggering times from available information, based on a Periodic Event Triggered Control (PETC) triggering function. In the case of no perturbation and full state information, the discrete times can be determined exactly, defining unions of cones in the state space. When bounded disturbances are present, we compute worst-case triggering times and their associated state-space regions. If full state information is also not available, we use a special observer to compute the worst-case triggering times, yielding an STC logic that only needs the current system output and the controller state. For all cases, we provide sufficient conditions for stability and L2-gain from disturbance to output.Team Tamas Keviczk
