Papers by Panos Antsaklis
Systems & control, 2014
In this paper the control of linear plants, where the sensor is connected to a linear controller/... more In this paper the control of linear plants, where the sensor is connected to a linear controller/actuator via a network is addressed. Both, state and output feedback, are considered and results are derived for both continuous and discrete plants. A key idea is that knowledge of the plant dynamics is used to reduce the usage of the network. Necessary and sufficient conditions for stability are derived as simple eigenvalue tests of a well-structured test matrix, constructed in terms of the update time h, and the parameters of the plant and of its model. These tests are extended to include network delay as well.
Structures Congress 2006, Oct 10, 2006
Given the present burdens associated with inspection and maintenance of Civil Infrastructure, the... more Given the present burdens associated with inspection and maintenance of Civil Infrastructure, the development of effective, automated damage diagnosis techniques, including the sensor technologies that support them, has become a major research need. While recent developments in wireless sensor networks have demonstrated their potential to provide continuous structural response data to quantitatively assess structural health, many important issues including network lifetime and stability, damage detection reliability, and trade-offs in model order to balance computational capabilities must be realistically addressed. Only then can wireless embedded sensor networks become a practical tool for Structural Health Monitoring of large, complex Civil Structures. In response to these needs, the concept of a multi-scale wireless sensor network is introduced in this study with a restricted input network activation scheme and the integration of data from a heterogeneous sensor array to improve damage detection for low-order models. The multi-scale network concept introduced here helps to improve power efficiency, minimize packet loss and latency, and eliminate synchronization issues through the use of a decentralized analysis scheme and the activation of sub-networks only in the vicinity of suspected damage, while reducing the required size of the reference pool for the undamaged state. This study introduces the network architecture concept, a strain-driven approach to damage detection and preliminary simulated results. Most research in these areas of "intelligent" structural assessment and evaluation retain the traditional architecture of a centralized data acquisition hub wired to tens or even hundreds of sensors. As cost effectiveness is a major concern, the installation and maintenance of these cabled systems represent significant concerns, prompting the move toward wireless sensor networks, particularly those with local processing capabilities, thus reducing the amount of data transmitted in power-consuming wireless radio communications. Early work in this area was led by Straser and Kiremidjian [1] and
IEEE Transactions on Automatic Control, Sep 1, 2004
arXiv (Cornell University), Feb 25, 2019
This paper presents a new data-driven fault identification and controller reconfiguration algorit... more This paper presents a new data-driven fault identification and controller reconfiguration algorithm. The presented algorithm relies only on the system's input and output data, and it does not require a detailed system description. The proposed algorithm detects changes in the input-output behavior of the system, whether due to faults or malicious attacks and then reacts by reconfiguring the existing controller. This method does not identify the internal structure of the system nor the extent and nature of the attack; hence it can quickly react to faults and attacks. The proposed method can be readily applied to various applications without significant modifications or tuning, as demonstrated by the examples in the paper.
arXiv (Cornell University), Sep 9, 2014
In this paper, we consider the problem of minimizing the exit rate with which a diffusion process... more In this paper, we consider the problem of minimizing the exit rate with which a diffusion process pertaining to a chain of distributed control systems, with random perturbations, exits from a given bounded open domain. In particular, we consider a chain of distributed control systems that are formed by n subsystems (with n ≥ 2), where the random perturbation enters only in the first subsystem and is then subsequently transmitted to the other subsystems. Furthermore, we assume that, for any ∈ {2,. .. , n}, the distributed control systems, which is formed by the first subsystems, satisfies an appropriate Hörmander condition. As a result of this, the diffusion process is degenerate, in the sense that the infinitesimal generator associated with it is a degenerate parabolic equation. Our interest is to establish a connection between the minimum exit rate with which the diffusion process exits from the given domain and the principal eigenvalue for the infinitesimal generator with zero boundary conditions. Such a connection allows us to derive a family of Hamilton-Jacobi-Bellman equations for which we provide a verification theorem that shows the validity of the corresponding optimal control problems. Finally, we provide an estimate on the attainable exit probability of the diffusion process with respect to a set of admissible (optimal) Markov controls for the optimal control problems.
arXiv (Cornell University), Sep 29, 2022
In this paper, we develop centralized and decentralized techniques for analyzing and synthesizing... more In this paper, we develop centralized and decentralized techniques for analyzing and synthesizing networked systems comprised of interconnected sets of non-linear subsystems-only using the subsystem dissipativity properties. In particular, this paper extends a recent work that proposed dissipativity based centralized analysis techniques for non-linear networked systems as linear matrix inequality (LMI) problems. First, we consider four networked system configurations (NSCs) of interest and provide centralized stability/dissipativity analysis techniques for them as LMI problems. Second, we show that the centralized interconnection topology synthesis techniques for these NSCs can also be developed as LMI problems. This enables synthesizing the interconnection topology among the subsystems so that specific stability/dissipativity measures of the networked system are optimized. Next, we show that the proposed analysis and synthesis techniques can be implemented in a decentralized and compositional manner (i.e., subsystems can be added/removed conveniently). Finally, we include several numerical results to demonstrate our contributions.
arXiv (Cornell University), May 6, 2014
We consider the problem of minimizing the asymptotic exit rate with which the controlled-diffusio... more We consider the problem of minimizing the asymptotic exit rate with which the controlled-diffusion process of a stochastically perturbed multi-channel dynamical system exits from a given bounded open domain. In particular, for a class of admissible bounded linear feedback operators, we establish a connection between the asymptotic exit rate with which such a controlled-diffusion process exits from the given domain and the asymptotic behavior (i.e., a probabilistic characterization) of the principal eigenvalue of the infinitesimal generator, which corresponds to the stochastically perturbed dynamical system, with zero boundary conditions on the given domain. Finally, we briefly remark on the implication of our result for evaluating the performance of the associated deterministic multi-channel dynamical system, when such a dynamical system is composed with a set of (sub)-optimal admissible linear feedback operators.
We consider the problem of stabilization and disturbance rejection in discrete time systems with ... more We consider the problem of stabilization and disturbance rejection in discrete time systems with limited feedback information as it is commonly the case in Networked Control Systems. In a networked system, transmission of information is constrained by the network bandwidth and availability. Our goal is to decrease the rate at which a perturbed system needs to transmit feedback information to update its controller node while maintaining stability and disturbance rejection properties. A state-disturbance observation approach is presented and we show in this paper that asymptotic stability can be obtained in the presence of constant disturbances. Additionally, we provide conditions for inter-update performance for both, constant and piece-wise constant disturbances. I. INTRODUCTION N Networked Control Systems (NCS) a digital communication network is used to transfer information among the components of a control system including actuators, controllers, and sensors. NCS differ significantly from classical control systems where all system components are attached directly to the control plant exchanging information using dedicated wiring [1]. The use of a shared communication channel for control systems makes feedback measurements inaccessible to the controller for long intervals of time. An approach followed by different authors is to keep the latest received feedback measurement constant until new information arrives from the controller, i.e. using a Zero-Order-Hold (ZOH), [2]-[4]. The use of a model of the system in the controller node provides better performance in general since an estimate of the state of the system can be used for control during the time intervals that feedback measurements are not available. Model-based frameworks have been used by different authors for control of networked systems [5]-[10], [12]-[17] or for control of systems with limited feedback communication [11]. The work in [5]-[11] considers model uncertainties and no external disturbances while the authors of [12]-[13] focus on attenuation of constant input disturbances by considering no plant-model mismatch. Similar model-based frameworks have been studied by different authors, for instance, the work in [14] considers discrete time systems subject to packet dropouts and the model dynamics are used to generate the control inputs when no feedback measurements are successfully received.
2022 IEEE 61st Conference on Decision and Control (CDC), Dec 6, 2022
We consider the problem of on-line evaluation of critical characteristic parameters such as the L... more We consider the problem of on-line evaluation of critical characteristic parameters such as the L2-gain (L2G), input feedforward passivity index (IFP) and output feedback passivity index (OFP) of non-linear systems using their inputoutput data. Typically, having an accurate measure of such system indices enables the application of systematic control design techniques. Moreover, if such system indices can efficiently be evaluated on-line, they can be exploited to device intelligent controller reconfiguration and fault-tolerant control techniques. However, the existing estimation methods of such system indices (i.e., L2G, IFP and OFP) are predominantly offline, computationally inefficient, and require a large amount of actual or synthetically generated input-output trajectory data under some specific initial/terminal conditions. On the other hand, the existing on-line estimation methods take an averagingbased approach, which may be sub-optimal, computationally inefficient and susceptible to estimate saturation. In this paper, to overcome these challenges (in the on-line estimation of system indices), we establish and exploit several interesting theoretical results on a particular class of fractional function optimization problems. For comparison purposes, the details of an existing averaging-based approach are provided for the same on-line estimation problem. Finally, several numerical examples are discussed to demonstrate the proposed on-line estimation approach and to highlight our contributions.
arXiv (Cornell University), Jul 5, 2022
In this paper, we consider the problem of platooning control with mismatched disturbances using t... more In this paper, we consider the problem of platooning control with mismatched disturbances using the distributed adaptive backstepping method. The main challenges are: (1) maintaining the compositionality and the distributed nature of the controller, and (2) ensuring the robustness of the controller with respect to general types of disturbances. To address these challenges, we first propose a novel notion that we named Vector String Lyapunov Function, whose existence implies l2 weak string stability. This notion is based on the vector Lyapunov function-based stability analysis, which depends on the inputto-state-stability of a comparison system. Using this notion, we propose an adaptive backstepping controller for the platoon such that the compositionality and the distributed nature of the controller can be ensured while the internal stability and string stability of the closed-loop system are formally guaranteed. Finally, simulation examples are provided to illustrate the effectiveness of the proposed control algorithm. In particular, we provide simulation results comparing our proposed control algorithm with a recently proposed control algorithm from the literature, under two types of information flow topologies and disturbances.
2022 American Control Conference (ACC), Jun 8, 2022
Piecewise affine (PWA) systems are widely applied in many practical cases such as the control of ... more Piecewise affine (PWA) systems are widely applied in many practical cases such as the control of nonlinear systems and hybrid dynamics. However, most of the existing PWA control methods have poor scalability with respect to the number of modes and system dimensions and may not be robust to the disturbances in performance. In this paper, we present a robust approximate simulation based control method for PWA systems under bounded external disturbances. First, a lower-dimensional linear system (abstraction) and an associated interface are designed to enable the output of the PWA system (concrete system) to track the output of the abstraction. Then, a Lyapunov-like simulation function is designed to show the boundedness of the output errors between the two systems. Furthermore, the results obtained for linear abstraction are extended to the case that a simpler PWA system is the abstraction. To illustrate the effectiveness of the proposed approach, simulation results are provided for two design examples.
arXiv (Cornell University), Apr 20, 2022
This paper considers the problem of decentralized analysis and control synthesis to verify and en... more This paper considers the problem of decentralized analysis and control synthesis to verify and ensure properties like stability and dissipativity of a large-scale networked system comprised of linear subsystems interconnected in an arbitrary topology. In particular, we design systematic networked system analysis and control synthesis processes that can be executed in a decentralized manner at the subsystem level with minimal information sharing among the subsystems. Compared to our most recent work on the same topic, we consider a substantially more generalized problem setup in this paper and develop decentralized processes to verify and ensure a broader range of networked system properties. We show that for such decentralized processes: (1) optimizing the used subsystem indexing scheme can substantially reduce the required inter-subsystem informationsharing sessions, and (2) in some network topologies, information sharing among only neighboring subsystems is sufficient (hence, distributed!). Moreover, the proposed networked system analysis and control synthesis processes are compositional/resilient to subsystem removals, which enable them to conveniently and efficiently handle situations where new subsystems are being added/removed to/from an existing network. We also provide significant insights into our decentralized approach so that it can be quickly adopted to verify and ensure properties beyond the stability and dissipativity of networked systems. En route to developing such decentralized techniques, we have also derived new centralized solutions for dissipative observer and dynamic output feedback controller design problems. Subsequently, we also specialize all the derived results for discrete-time networked systems. We conclude this paper by providing several simulation results demonstrating the proposed novel decentralized analysis and control synthesis processes and dissipativity-based results.
arXiv (Cornell University), Jun 10, 2017
This paper summarizes important results useful for controller design of multi-input multi-output ... more This paper summarizes important results useful for controller design of multi-input multi-output systems. The main goal is to characterize the stabilizing controllers that provide a desired response.
arXiv (Cornell University), Mar 24, 2017
In this report, we introduce a comprehensive design framework for Event-Triggered Networked Contr... more In this report, we introduce a comprehensive design framework for Event-Triggered Networked Control Systems based on the passivity-based concept of Input Feed-Forward Output Feedback Passive (IF-OFP) systems. Our approach is comprehensive in the sense that we show finite-gain L 2-stability and robustness for the networked control system by considering the effects of time-varying or constant network induced delays, signal quantizations, and data losses in communication links from the plant to controller and the controller to plant. Our design is based on the need for a more efficient utilization of band-limited shared communication networks which is a necessity for the design of Large-Scale Cyber-Physical systems. To achieve this, we introduce simple triggering conditions that do not require the exact knowledge of the subsystems and are located on both sides of the communication network: the plant's output and the controller's output. This specifically leads to a great decrease in the communication rate between the controller and plant. Additionally, we show lower-bounds on inter-event time intervals for the triggering conditions and show the design's robustness against external noise and disturbance. We illustrate the relationship amongst stability, robustness and passivity levels for the plant and controller. We analyze our design's robustness against packet dropouts and loss of communication. Our results are design-oriented in the sense that based on our proposed framework, the designer can easily observe the trade-offs amongst different components of the networked control system, time-varying delays, effects of signal quantizations and triggering conditions, stability, robustness and performance of networked control system and make design decisions accordingly.
arXiv (Cornell University), 2015
In this report, we apply an input-output transformation passivation method, described in our prev... more In this report, we apply an input-output transformation passivation method, described in our previous works, to an Adaptive Cruise Control system. We analyze the system's performance under a co-simulation framework that makes use of an online optimization method called extremum-seeking to achieve the optimized behavior. The matrix for passivation method encompasses commonly used methods of series, feedback and feed-forward interconnections for passivating the system. We have previously shown that passivity levels can be guaranteed for a system using our passivation method. In this work, an extremum-seeking algorithm was used to determine the passivation parameters. It is known that systems with input-output timedelays are not passive. On the other hand, time-delays are unavoidable in automotive systems and commonly emerge in software implementations and communication units as well as driver's behavior. We show that by using our passivation method, we can passivate the system and improve its overall performance. Our simulation examples in CarSim and Simulink will show that the passive system has a considerably better performance.
─The problem of output feedback control of nonlinear discrete-time systems connected over a netwo... more ─The problem of output feedback control of nonlinear discrete-time systems connected over a network is studied in this paper. The Model-Based Networked Control Systems (MB-NCS) scheme is used to reduce communication to free up network resources for other applications. This is done by implementing an approximate model of the plant at the controller node to predict plant output values between sensor measurements. Communication is further reduced by considering an aperiodic event-triggered communication scheme that transmits data only when the error in the output exceeds a specified threshold. With the model and aperiodic updates, the plant is able to operate in open-loop for relatively large time intervals while still maintaining a desired level of accuracy in the control signal. When control systems are allowed to operate in open-loop like this, they often become sensitive to unmodeled dynamics. This paper considers model mismatch between the plant and model as well as bounded disturbances that may cause performance issues. In this paper, the model-based network architecture is represented as a standard negative feedback design problem for analysis purposes. Dissipative theory is applied to the feedback system for stability analysis and control synthesis. The results provide average squared boundedness with a constructive bound of the system output despite the presence of aperiodic updates, nonlinear dynamics, model uncertainties, and external disturbances. I.
arXiv (Cornell University), Sep 28, 2017
In this paper, we show synchronization for a group of output passive agents that communicate with... more In this paper, we show synchronization for a group of output passive agents that communicate with each other according to an underlying communication graph to achieve a common goal. We propose a distributed event-triggered control framework that will guarantee synchronization and considerably decrease the required communication load on the band-limited network. We define a general Byzantine attack on the event-triggered multi-agent network system and characterize its negative effects on synchronization. The Byzantine agents are capable of intelligently falsifying their data and manipulating the underlying communication graph by altering their respective control feedback weights. We introduce a decentralized detection framework and analyze its steady-state and transient performances. We propose a way of identifying individual Byzantine neighbors and a learning-based method of estimating the attack parameters. Lastly, we propose learning-based control approaches to mitigate the negative effects of the adversarial attack. I. INTRODUCTION Distributed coordination of multi-agent systems has been discussed extensively in control, communication and computer science literature. The wide range of applications in this area includes multiple robot coordination [1], cooperative control of vehicle formations [2], flocking [3] and spacecraft formation flying [4]. A strong body of literature exists on the state synchronization of homogeneous multi-agent systems with identical dynamics. In many practical Arash Rahnama and Panos J.
Human controllers as pilots or drivers can be described by linear time invariant systems cascaded... more Human controllers as pilots or drivers can be described by linear time invariant systems cascaded with time delay. Inspired by this, we 'generalize' the definition of passivity index to irrational transfer functions and use the passivity index to examine passivity of some existing human models. The results show that the human model is non-passive due to the time delay which represents inherent human limitations. We then propose a passification scheme when a human operator is in the loop. By this scheme, the closed-loop system with human in the loop as a controller can have desired positive passivity indices to address the control tasks of interest.
When network induced delays are considered in the event-triggered control literature, they are ty... more When network induced delays are considered in the event-triggered control literature, they are typically delays from the plant to the network controller and a tight bound on the admissible delays is usually imposed based on the analysis of inter-event time to guarantee stability of the event-triggered control systems. In this paper, we introduce a framework for output feedback based event-triggered networked control systems(NCSs). The triggering condition is derived based on passivity theorem which allows us to characterize a large class of output feedback stabilizing controllers. The proposed set-up enables us to consider network induced delays both from the plant to the network controller and from the network controller to the plant. We also take quantization of the transmitted signals in the communication network into consideration and we show that finite-gain L 2 stability can be achieved in the presence of time-varying (or constant) network induced delays with bounded jitters, without requiring that the network induced delays are upper bounded by the inter-event time.
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Papers by Panos Antsaklis