Anas Fattouh

Robust observer design for time-delay systems: a Riccati equation approach

This problem has been solved by Watanabe et al. [14], [13] by introducing a distributed time-delay in the observer dynamic system. Also, Pearson et al. [10] and Ramos et al. [12] have built observers for delayed-state systems by computing the unstable eigenvalues of the system under consideration which, in some case, may be a very difficult numerical problem [7]. In those papers the robustness issues have not been considered. Yao et al. [15] have used a factorization approach in order to parameterize some observers for time-delay systems, however, no explicit procedure is given to obtain the observer.

A LMI approach to robust observer design for linear time-delay systems

This paper is concerned with a robust observer design for linear time-delay systems via linear matrix inequality approach. The proposed method not only guarantees the stability of the proposed observer, but also reduces the effects of different unstructured uncertainties on the estimated error.

H∞ controller and observer design for linear systems with point and distributed time-delays

Abstract A memoryless state feedback control law is developed such that the closed-loop system containing point and distributed time-delays is asymptotically stable and the H ∞ -norm of the transfer function from the disturbance to the controlled output is reduced to some predefined level. The feedback is obtained by solving a parameter-dependent linear matrix inequality. When the state variables are not available, an observer is built using a similar technique which generates an estimation of the state variables in order to implement the above state feedback.

H ∞ -Based impedance control of teleoperation systems with time delay 1

Abstract Impedance control is used to adjust the dynamic relationship between the position of a manipulator and the applied forces when it interacts with the environment. In bilateral teleoperation systems, communication time delay may destabilize the closed-loop system and certainly degrade the operator’s intuition and performance. In this paper, a new scheme for impedance control of bilateral teleoperation systems in the presence of communication time delay is proposed. Local controller for master manipulator is firstly designed in order to get a specified master impedance. Then, a global controller is designed based on H ∞ framework such that the global system, including communication time delay, is stable and the desired impedance characteristic of the slave manipulator is achieved asymptotically.

Further results on unknown input observers design for time-delay systems

This paper presents new necessary and sufficient conditions for the existence of unknown input observers for linear time-delay systems.

Robust H ∞ Control of Bilateral Teleoperation Systems Under Communication Time-Delay

In this chapter we consider the problem of robust control of bilateral teleoperation systems subject to communication time-delay. The stability of system under consideration is firstly analyzed and a sufficient condition for delay-independent stability is provided. Then the robustness issue is considered, and the problem of controller design that robustly stabilizes the system independently of time-delay w.r.t environment uncertainties is formulated as an H ∞ problem which can be solved using efficient algorithms. When delay independent stability cannot be achieved, a method to determine the maximal allowed time-delay is provided for which the system stability is guaranteed. Simulation results point out the interest of the proposed approach.

Pulse Controller Design for Linear Time-Delay Systems

Abstract The problem of digital redesign of control laws containing distributed time delays for linear systems with delayed state and control is addressed in this paper. The continuous controller with distributed time delays is approximated by a discrete one with only point time delays using a set of block-pulse functions.

A Model Matching Solution of Robust Observer Design for Time-Delay Systems

Uncertainties arc unavoidable in practical situations and they have to be taken into consideration in control system design. In this chapter, a method for designing a robust observer for linear time-delay systems is proposed. Under the assumption that the considered time-delay system is spectrally controllable and spectrally observable, a double Bezout factorization of its nominal transfer matrix is obtained. Next, based on this factorization, all stable observers for the nominal system are parameterized. By applying those observers on the real system, the parameterization transfer matrix has to be found such that the error between the real estimation and the nominal one is minimized. This problem is rewritten as an infinite dimensional model matching problem for different types of uncertainty. In order to solve this infinite dimensional model matching problem, it is transformed into a finite dimensional one, and therefore a suboptimal solution can be obtained using existing algorithms.

Finite spectrum assignment controller for teleoperation systems with time delay

In this paper, two controllers are proposed for bilateral teleoperation systems with communication time delay. The first one guarantees the tracking of slave-master outputs, while the second one guarantees the transparency. Communication time delay appears in the control loop of the second controller, and finite spectrum assignment method is used to design this controller such that the resulting closed-loop system have a desirable finite spectrum. Numerical example shows that both tracking and transparency can be guaranteed using the proposed method.