Pietro Tesi

Unfalsified Virtual Reference Adaptive Switching Control of Plants with Persistent Disturbances

Abstract This paper addresses virtual reference adaptive switching control whereby a data-driven supervisor aims at stabilizing an unknown time-invariant dynamic system by switching at any time in feedback with system one element from a finite family of candidate controllers. Under the only assumption of problem feasibility, viz. the controller family contains a stabilizing controller, the resulting switched system is shown to be stable against arbitrary exogenous persistent bounded disturbances.

Model-Free Adaptive Switching Control of Uncertain Time-Varying Plants

Abstract This paper addresses the problem of controlling an uncertain time-varying plant by means of a finite family of linear candidate controllers supervised by an appropriate switching logic. It is shown that global stability of the closed-loop system can be guaranteed provided that (i) at every time there is at least one candidate controller that would stabilize the current time-invariant “frozen” plant model, and (ii) the changes in the plant model are infrequent.

Input-to-State Stabilizing Control Under Denial-of-Service

The issue of cyber-security has become ever more prevalent in the analysis and design of networked systems. In this paper, we analyze networked control systems in the presence of denial-of-service (DoS) attacks, namely attacks that prevent transmissions over the network. We characterize frequency and duration of the DoS attacks under which input-to-state stability (ISS) of the closed-loop system can be preserved. To achieve ISS, a suitable scheduling of the transmission times is determined. It is shown that the considered framework is flexible enough so as to allow the designer to choose from several implementation options that can be used for trading-off performance versus communication resources. Examples are given to substantiate the analysis.

Stability of Unfalsified Adaptive Switching Control in Noisy Environments

In recent years, unfalsified adaptive switching control has emerged as a promising technique for the control of uncertain plants only on the basis of plant I/O data. This note analyzes the input-output stability of the resulting switched system in a noisy environment, and discusses the issue of equivalence among different input-output stability notions.

Model-Free Adaptive Switching Control of Time-Varying Plants

This paper addresses the problem of controlling an uncertain time-varying plant by means of a finite family of candidate controllers supervised by an appropriate switching logic. It is assumed that, at every time, the plant consists of an uncertain single-input/single output linear system. It is shown that stability of the switched closed-loop system can be ensured provided that 1) at every time there is at least one candidate controller capable of potentially stabilizing the current time-invariant “frozen” plant model, and 2) the plant changes are infrequent or satisfy a slow drift condition.

Resilient Control under Denial-Of-Service

We investigate resilient control strategies for linear systems under Denial-of-Service (DoS) attacks. By DoS attacks we mean interruptions of communication on measurement (sensor-to-controller) and control (controller-to-actuator) channels carried out by an intelligent adversary. We characterize the duration of these interruptions under which stability of the closed-loop system is preserved. The resilient nature of the control descends from its ability to adapt the sampling rate to the occurrence of the DoS.

Event-Triggered Control Systems Under Denial-of-Service Attacks

In this paper, we propose a systematic design framework for output-based dynamic event-triggered control (ETC) systems under denial-of-service (DoS) attacks. These malicious DoS attacks are intended to interfere with the communication channel causing periods in time at which transmission of measurement data is impossible. We show that the proposed ETC scheme, if well designed, can tolerate a class of DoS signals characterized by frequency and duration properties without jeopardizing the stability, performance and Zeno-freeness of the ETC system. In fact, the design procedure of the ETC condition allows tradeoffs between performance, robustness to DoS attacks, and utilization of communication resources. The main results will be illustrated by means of a numerical example.

Stabilization and tracking for switching linear systems under unknown switching sequences

This paper describes recent progress in the study of switching linear systems i.e. linear systems whose dynamics can switch among a family of possible configurations/modes. The attention is focused on those classes of switching systems governed by unknown switching sequences. For this case, we address the problem of devising suitable control actions able to stabilize the plant and regulate its output about a desired reference trajectory. The approach considered in this paper consists in designing a suitable family of feedback controllers and a mode-estimator that at any time determines which candidate controller has to be placed in the feedback loop on the grounds of a real-time estimate of the current plant mode. It is shown that, even if a correct reconstruction of the plant mode from the measured data is not always possible, under certain conditions, exponential stability of the closed-loop can be guaranteed for any slow-on-the-average plant switching sequence.

Observer-Based Control Techniques for the LBT Adaptive Optics under Telescope Vibrations

This paper addresses the application of observer-based control techniques for the adaptive optics system of the LBT telescope. In such a context, attention is focused on the use of Kalman and H∞ filters to estimate the temporal evolution of phase perturbations due to the atmospheric turbulence and the telescope vibrations acting on tip/tilt modes. We shall present preliminary laboratory experiments carried out at the Osservatorio Astrofisico di Arcetri using the Kalman filter.

Adaptive memory in multi-model switching control of uncertain plants

This paper describes some recent results in multi-model switching control. The scheme here considered embeds a finite family of pre-designed controllers and a high-level unit which selects, at each instant of time, the candidate controller to be placed in feedback to the uncertain plant. The study considers a switching strategy where controller selection is based on windowed cost functions. The key feature of the proposed strategy is that the window (the memory) is not kept constant, but, on the contrary, is adjusted on-line, on the grounds of measured data. The potential benefits of using an adaptive memory switching strategy are discussed and illustrated through a benchmark example.