Analysis of Linear Time Invariant Systems With Time Delay

1992 ◽  
Vol 114 (4) ◽  
pp. 544-555 ◽  
Author(s):  
K. Youcef-Toumi ◽  
S. Reddy
Keyword(s):  
Time Delay ◽  
Continuous Time ◽  
Control Algorithm ◽  
Closed Loop ◽  
Linear Time ◽  
Necessary Condition ◽  
Closed Loop System ◽  
Time Delay Control ◽  
Delay Control ◽  
Continuous Time Delay

Time Delay Control has recently been suggested as an alternative scheme for control of systems with unknown dynamics and unpredictable disturbances. The proposed control algorithm does not require an explicit plant model nor does it depend on the estimation of specific plant parameters. Rather, it uses information in the recent past to directly estimate the unknown dynamics at any given instant, through time delay. In earlier papers, analysis and implementation of Time Delay Controller for nonlinear systems were discussed. This paper analyzes the continuous Time Delay Controller for a class of linear systems and presents necessary and sufficient conditions for control system stability. A necessary condition for stability is derived using the properties of linear time-delayed systems. This condition involves only a few of the system and controller parameters and facilitates design of the Time Delay Controller. It is proved that this necessary condition is also sufficient if the delay time is chosen to be infinitesimally small. The convergence of closed loop system error to zero for certain classes of inputs and disturbances when the system is stable is also established. It is also shown that certain approximations in the control algorithm and certain additional unmodeled dynamics render the closed loop system under continuous Time Delay Control to be not exponentially stable due to the controller poles on the imaginary axis at infinitely high frequencies. However, in digital implementation, all the signals are prefiltered by anti-aliasing filters prior to sampling. Hence, the highest frequency component is automatically limited and the issue of exponential instability is not encountered. A discussion is presented comparing Time Delay Control with Repetitive Control. It is indicated that the Time Delay Controller can perform the functions of a repetitive controller with the delay time replaced by the period of the reference input while the repetitive controller can perform the functions of Time Delay Controller for sufficiently small “period” for a certain class of linear systems. Furthermore, examples are included to illustrate the results.

New Stability Analysis and Design of Discrete Time Delay Control for Nonaffine Nonlinear Systems

2020 ◽  
Author(s):  
Suresh B. Reddy
Keyword(s):  
Time Delay ◽  
Nonlinear Systems ◽  
Discrete Time ◽  
Continuous Time ◽  
Time Delay Control ◽  
Uncertain Dynamics ◽  
Discrete Time Delay ◽  
Delay Control ◽  
Continuous Time Delay ◽  
Nonaffine Nonlinear Systems

Abstract Time Delay Control (TDC) for linear and nonlinear systems with uncertain dynamics has been widely discussed in the literature, as it has a very simple and compact form. It uses time-delayed signals for estimating unknown dynamics at an instant, and uses feedback linearization for cancellation of known and estimated unknown dynamics. While the original formulation and most of the analyses have been focused on the continuous version of the controller, its implementation is more natural in digital form. This paper extends the recently improved sufficient Bounded Input - Bounded Output (BIBO) stability conditions for continuous Time Delay Control of nonaffine nonlinear systems to discrete Time Delay Control, including simplified approximate conditions under various assumptions. Additionally. asymptotic stability is established for similar conditions. The derived conditions are contrasted with earlier results for continuous Time Delay Control. Examples are used to illustrate the differences in continuous and discrete TDC, related to performance as well as sufficient and actual conditions for stability.

scholarly journals Robust-adaptive dynamic programming-based time-delay control of autonomous ships under stochastic disturbances using an actor-critic learning algorithm

2021 ◽  
Author(s):  
Hossein Nejatbakhsh Esfahani ◽  
Rafal Szlapczynski
Keyword(s):  
Dynamic Programming ◽  
Time Delay ◽  
Control Algorithm ◽  
Approximate Dynamic Programming ◽  
Robust Adaptive Control ◽  
Stochastic Disturbances ◽  
Time Delay Control ◽  
Model Free ◽  
Delay Control ◽  
Robust Adaptive

AbstractThis paper proposes a hybrid robust-adaptive learning-based control scheme based on Approximate Dynamic Programming (ADP) for the tracking control of autonomous ship maneuvering. We adopt a Time-Delay Control (TDC) approach, which is known as a simple, practical, model free and roughly robust strategy, combined with an Actor-Critic Approximate Dynamic Programming (ACADP) algorithm as an adaptive part in the proposed hybrid control algorithm. Based on this integration, Actor-Critic Time-Delay Control (AC-TDC) is proposed. It offers a high-performance robust-adaptive control approach for path following of autonomous ships under deterministic and stochastic disturbances induced by the winds, waves, and ocean currents. Computer simulations have been conducted under two different conditions in terms of the deterministic and stochastic disturbances and all simulation results indicate an acceptable performance in tracking of paths for the proposed control algorithm in comparison with the conventional TDC approach.

Stability of Uncertain Linear Systems With Time Delay

1991 ◽  
Vol 113 (4) ◽  
pp. 558-567 ◽  
Author(s):  
K. Youcef-Toumi ◽  
J. Bobbett
Keyword(s):  
Time Delay ◽  
Linear Time ◽  
Sufficient Condition ◽  
Single Input Single Output ◽  
Time Delay Control ◽  
Linear Time Invariant ◽  
Single Output ◽  
Uncertain Dynamics ◽  
Delay Control ◽  
The Stability

The control of systems with uncertain dynamics and unpredictable disturbances has raised some challenging problems. This is particularly important when high system performance is to be guaranteed at all times. Recently, Time Delay Control has been suggested as an alternative control scheme. The proposed control system does not require an explicit plant model nor does it depend on the estimation of specific plant parameters. Rather, it combines adaptation with past observations to directly estimate the effect of the plant dynamics. This paper outlines the Time Delay Control law for a class of linear dynamic systems and then presents a sufficient condition for stability of linear uncertain systems with time delay. The ideas of Nyquist and Kharitonov are used in the development of a sufficient condition, which does not resort to using approximations for time delay. Like Nyquist, the condition depends on maps of the Nyquist path and, like Kharitonov, stability depends on four functions each yielding a stable system. In this paper we combine these ideas to determine the stability of systems where the Time Delay Controller is applied to single input single output, linear time-invariant plants whose coefficients are known to vary within certain defined intervals. The development is carried out in the context of Time Delay Control but it can be applied in more general cases. Two examples will illustrate the approach and the usefulness of the technique.

Robust Passivity Control for Uncertain Time-Delayed Systems

2010 ◽  
Vol 29-32 ◽  
pp. 2025-2030
Author(s):  
Gui Fang Li ◽  
Yong Cheng Sun ◽  
Sheng Guo Huang
Keyword(s):  
Time Delay ◽  
Closed Loop ◽  
Passive Control ◽  
Linear Time ◽  
Linear Matrix ◽  
Closed Loop System ◽  
Parameter Uncertainties ◽  
Delayed Systems ◽  
Controller Gain ◽  
Uncertain Time

This paper focuses on the robust passivity synthesis problem for a class of linear time-delayed systems subject to parameter uncertainties. The time delay is assumed to be unknown, and the parameter uncertainties are allowed to appear in all matrices of the model. The aim lies in designing observer-based dynamic controller that render the closed-loop system be strongly robustly stable and strict passive for all admissible uncertainties, independently of time delay. Using a scaling parameterization approach, the problem being considered is transformed into a class of strongly stable and strictly passive control problem for a parameterized system without uncertainties. And then, the controller gain and the observer gain are obtained in terms of a linear matrix inequality. Finally, a numerical example is provided to demonstrate the validity of the proposed approach.

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