Mbg Marieke Cloosterman

Controller synthesis for networked control systems

This paper presents a discrete-time model for networked control systems (NCSs) that incorporates all network phenomena: time-varying sampling intervals, packet dropouts and time-varying delays that may be both smaller and larger than the sampling interval. Based on this model, constructive LMI conditions for controller synthesis are derived, such that stabilizing state-feedback controllers can be designed. Besides the proposed controller synthesis conditions a comparison is made between the use of parameter-dependent Lyapunov functions and Lyapunov-Krasovskii functions for stability analysis. Several examples illustrate the effectiveness of the developed theory.

Robust Stability of Networked Control Systems with Time-varying Network-induced Delays

In this paper, the stability of a networked control system (NCS) with time-varying delays is analyzed. A discrete-time state-space model is used to analyze the dynamics of the NCS. The delay is introduced by the network itself and is assumed to be upperbounded by a fraction of the sample-time. A typical motion control example is presented in which the time-variation of the delay results in an unstable system, although for each fixed delay the system is stable. Conditions in terms of LMIs are presented guaranteeing the robust asymptotic stability of the discrete-time system, given bounds on the uncertain time-varying delay. Moreover, it is shown that the robust stability conditions also guarantee asymptotic stability of the intersample behavior. Additionally, LMIs are presented to synthesize a feedback controller that stabilizes the system for the uncertain time-varying delay. The results are illustrated on an example concerning a mechanical model of a motor driving a roller in a printer

Stability of networked control systems with large delays

This paper proposes stability analysis techniques for networked control systems (NCSs) with uncertain, time- varying network-induced delays. A discrete-time model, describing an NCS with delays, that can be both smaller and larger than the sampling interval, is presented. This model includes the effects of message rejection and vacancy sampling. The conditions are kept less conservative by exploiting the real Jordan form of the continuous-time model in the discretization. Based on this discrete-time NCS model sufficient LMI conditions are proposed for the stability analysis.

Stabilization of Networked Control Systems with large delays and packet dropouts

We consider the stabilization problem for networked control systems (NCSs) with uncertain, time-varying network-induced delays and a bounded number of subsequent packet dropouts. A discrete-time model, describing a NCS with packet dropouts and time-varying delays, that can be both smaller and larger than the sampling interval, is presented. Based on this NCS model sufficient LMI conditions are proposed for the stability analysis and controller synthesis problem for two different controllers, i.e. a feedback controller that depends on both the state and the past control inputs and a state-feedback controller. The applicability of both controllers is compared. Moreover, the stability and controller synthesis LMIs allow for a performance analysis in terms of a lower bound for the transient decay rate of the response. The results are illustrated by application to a typical motion control example.

Tracking control for networked control systems

A solution to the approximate tracking problem for networked control systems (NCSs) with uncertain, time-varying sampling intervals and network delays is presented. The uncertain, time-varying sampling and delays cause inexact feedforward, which induces a perturbation on the tracking error dynamics. Two alternative modeling approaches are used: a discrete-time model and a model in terms of delay impulsive differential equations. Sufficient conditions for the input-to-state stability (ISS) of the tracking error dynamics with respect to this perturbation are given. These ISS results provide bounds on the steady-state tracking error as a function of the plant properties, the controller parameters, and the network properties. The results are illustrated on a mechanical motion control example.

Comparison of stability characterisations for networked control systems

This paper presents linear matrix inequalities for stability analysis for networked control systems (NCSs) that incorporates various network phenomena: time-varying sampling intervals, packet dropouts and time-varying delays that may be both smaller and larger than the sampling interval. The problem is approached from a discrete-time modelling perspective. A comparison is made between the use of Parameter Dependent Lyapunov functions and Lyapunov-Krasovskii functions for stability analysis. Examples illustrate the developed theory.