Artificial Time Delay Research Articles

Strengthening stability with centralized event-triggered control system with the disturbances and artificial time delay in wireless connected vehicle platooning (CVSs)

This paper addresses the difficulties with connected vehicle systems (CVSs), particularly with vehicle platooning, are examined in this paper. For leader and follower-connected vehicles, the control protocol (which includes artificial delays, disturbances and proportional gains) is implemented. With tracking error systems, system dynamics are modelled while taking outside influences into consideration. Using creative thinking, a centralized event-triggered control system is implemented to maximize fleet wide communication updates. System stability is guaranteed by this centralized method in combination with quadratic form Lyapunov stability analysis. The risk of zeno behaviour is reduced by an event-triggered communication condition that is activated when a threshold is exceeded. The effectiveness of the centralized event-triggered system in improving stability and resilience in connected vehicle platooning scenarios is evaluated numerically through simulations.

Sliding mode controller design via delay-dependent H_{infty } stabilization criterion for load frequency regulation

This work presents a control approach based on sliding-mode-control (SMC) to design robust H_{infty } state feedback controllers for load frequency regulation of delayed interconnected power system (IPS) with parametric uncertainties. Considering both state feedback control strategy and delayed feedback control strategy, two SMC laws are proposed. The proposed control laws are designed to improve the stability and disturbance rejection performance of delayed IPS, while stabilization criteria in the form of linear matrix inequality are derived by choosing a Lyapunov–Krasovskii functional. An artificial time-delay is incorporated in the control law design of the delayed feedback control structure to enhance the controller performance. A numerical example is considered to study the control performance of the proposed controllers and simulation results are provided to observe the dynamic response of the IPS.

Bumpless transfer distributed adaptive backstepping control of nonlinear multi-agent systems with circular filtering under DoS attacks

This paper studies the problem of resilient distributed cooperative control for a class of uncertain nonlinear multi-agent systems (MASs) under Denial-of-Service (DoS) attacks. To avoid repeatedly differentiating the discontinuous communication signals caused by the DoS attacks in the backstepping procedure, a new circular switching filter is constructed. Compared with the existing results, the circular switching filter can sufficiently improve the tolerance capacity for the DoS attacks in the sense that the DoS attacks can be tolerated as long as the network under attacks is intermittently connected. To address the issue of discontinuity of the switching controller, a bumpless transfer controller is further proposed by smoothing the discontinuous communication signals based on an artificial time delay mechanism. Simulation results illustrate the effectiveness of the proposed control schemes.

Recoil attenuation for deepwater drilling riser systems via delayed [formula omitted] control

This paper deals with the recoil suppression problem of a deepwater drilling riser system via active H∞ control using both current and delayed states. First, based on the three degrees of freedom spring–mass–damping model of the riser system, an incremental dynamic equation of the system subject to the platform heave motion and the friction force induced by drilling discharge mud and seawater is established. Then, to reject recoil movements of the riser, a delayed state feedback H∞ controller with delayed states as well as current states is designed. The existence conditions and the design method of the delayed H∞ recoil controllers are presented. Third, the effects of the introduced time-delays on the recoil control of the riser are analyzed, and the design of optimal artificial time-delays is formulated as the minimum value problem of a series of quintic algebraic polynomials, which are related to the weights of average response amplitudes, steady-state errors, and the control force. Lastly, simulation results are provided to demonstrate the effectiveness of delay-free and delayed H∞ recoil control schemes for the riser. It is shown that (i) under the delayed H∞ controllers, the recoil responses of the riser can be controlled significantly; (ii) the decay rate of the recoil response under the delay-free H∞ controller is slightly faster than the one under the delayed H∞ controllers. However, the former requires more control cost than the latter; (iii) compared with the delayed H∞ controller with the existing linear quadratic optimal controller, the control cost by the former is larger than that by the latter. However, the steady-state errors of the riser under the latter are slightly smaller than that under the former; (iv) the introduced time-delays with proper size play positive role of suppressing recoil response of the system, and the corresponding delayed H∞ controller series provide more options for recoil control of the riser.

Networked control systems with probabilistic time-varying delay based on event-triggered non-fragile [formula omitted] control

The non-fragile H∞ problem for networked control systems with probabilistic time-varying delay, stochastic nonlinear, controller gain fluctuation and adaptive event-triggered mechanism is studied. The random interval delay, nonlinear fluctuation and gain fluctuation of the controller all obey a certain uncorrelated Bernoulli distribution white noise sequence. An improved time continuous delay system model for networked control systems is constructed by using input delay method. A two-sided closed-loop Lyapunov–Krasovskii functional is constructed considering the sawtooth structure of artificial time delay, and the asymptotically stable conditions of closed-loop system with little conservatism are obtained. A non-fragile H∞ control strategy based on adaptive event-triggered is proposed and the co-design method for gain matrix of the non-fragile controller and event-triggered matrix is obtained. Finally, the effectiveness of the proposed method is verified by two simulation examples.

Non-fragile H ∞ control for event-triggered networked control systems with probabilistic time-varying delay

This paper studies the non-fragile output-feedback control problem for event-triggered networked control system with probabilistic time-varying delay and controller gain uncertainties. With known conditional probability distribution, the time-varying delay is modelled as a Bernoulli distributed white sequences. An improved two-side closed-loop functional is constructed by using the sawtooth structure characteristic of artificial time delay. By applying the Lyapunov–Krasovskii stability theory, the lower conservative stability criterions for time-delay system are derived. Aiming at the external disturbance and the parameter uncertainty of controller gain, a non-fragile output-feedback control strategy based on event-triggered mechanism is proposed. Moreover, a co-design scheme of controller gain and event-triggered matrix is obtained based on linear matrix inequality technique. Finally, three simulation examples are utilised to verify the effectiveness of the presented method.

Control of Electrical Generators Based on Low-pass Filter and Artificial Time-delay

The paper describes a novel control law for control of network of electrical generators under parametric uncertainty, disturbances and measurement noises. To reduce the influence of measurement noises the low-pass filter is considered. The control law based on using the artificial time-delays that allows to stabilize the closed-loop system and do not use observers. As a results, the free observer control law is less sensitive to measurement noises.

DrStabilization: A Matlab-based Software to Design Structured Time-delay Controllers

A new Matlab-based software called DrStabilization is introduced. The main purpose of the software is to stabilize multi-input multi-output linear time-invariant systems which may have an arbitrary number of discrete time-delays. The stabilization problem is formulated as the minimization of spectral abscissa function over the controller parameters. By modifying this problem, it is also possible to consider strong stability, i.e., stability achieved by a stable controller. The software allows designing structured dynamic output feedback controllers. By structuring the controller matrices, one can design decentralized controllers and/or well-known servocompansators such as PI/PID/PIR. Furthermore, the software also allows designing time-delay controllers in which case an arbitrary number of artificial time-delays can be introduced both to the I/O channels and the dynamics of the controller itself. The utilization of the software is illustrated through an example.

Communication constrained robust guidance strategy using quantized artificial time delay based control with input saturation

This work proposes the use of a logarithmic quantizer to minimize the computational load on the onboard processor of missiles. The quantizer output discretizes the continuous guidance command to a finite set of predefined discrete levels. This in turn puts an end to the need for installing a powerful state of the art modern processor onboard a missile, while enabling designers to install a comparatively cost efficient and compact processor. To include robustness properties, the proposed guidance strategy adopts the artificial time-delayed control (TDC) philosophy. The use of TDC methodology eliminates the conservative assumptions of a priori knowledge about uncertainty bounds as required by most state-of-the-art robust control schemes. Thus, the proposed guidance law is able to achieve interception even in the presence of uncertainties while significantly reducing control updates due to the use of input quantizer. Input saturation is also considered for the proposed quantized time-delay control (QTDC) based guidance strategy. The Uniformly Ultimately Bounded (UUB) convergence of the closed-loop system states is demonstrated through the Lyapunov theory. Simulation studies involving various engagement scenarios and a comparative performance study of the QTDC guidance scheme with the conventional periodic time-triggered TDC technique are provided to highlight the efficacy of the proposed approach. In this work, a quantized input time delay based control is used to significantly reduce the control updates while designing an efficient robust control strategy. A sense of time-energy efficiency is introduced for the overall system and input saturation is also considered.

Design of time-delayed safety switches for CRISPR gene therapy

CRISPR system is a powerful gene editing tool which has already been reported to address a variety of gene relevant diseases in different cell lines. However, off-target effect and immune response caused by Cas9 remain two fundamental problems. Inspired by previously reported Cas9 self-elimination systems, time-delayed safety switches are designed in this work. Firstly, ultrasensitive relationship is constructed between Cas9-sgRNA (enzyme) and Cas9 plasmids (substrate), which generates the artificial time delay. Then intrinsic time delay in biomolecular activities is revealed by data fitting and utilized in constructing safety switches. The time-delayed safety switches function by separating the gene editing process and self-elimination process, and the tunable delay time may ensure a good balance between gene editing efficiency and side effect minimization. By addressing gene therapy efficiency, off-target effect, immune response and drug accumulation, we hope our safety switches may offer inspiration in realizing safe and efficient gene therapy in humans.

Maneuvering control of planar snake robot: An adaptive robust approach with artificial time delay

AbstractThis article proposes an adaptive‐robust maneuvering control framework for a planar snake robot under the influence of parameter uncertainties. The entire control objective of maneuvering control can be viewed as the simultaneous establishments of two goals: one to maintain a time‐varying body shape of the snake robot for consistent motion (called the outer layer) and the other dealing with the velocity and head‐angle tracking of the same (called the inner layer). Unknown variations in the ground friction coefficients have been considered to be the primary source of time‐varying uncertainties which affects the control performance in both the layers. Accordingly, an artificial time delay‐based adaptive‐robust control (ARC) framework, dual adaptive‐robust time‐delayed control (ARTDC), is proposed. The term dual signifies simultaneous application of ARTDC for the outer as well as the inner layer. ARTDC comprises of two segments: an artificial time delay‐based time‐delayed estimation (TDE) part and an ARC part. While TDE approximates the completely unknown friction forces, the ARC tackles the approximation error arising from the TDE. More importantly, compared with the existing ARC methodologies, the proposed ARTDC neither presumes the overall uncertainty to be upper bounded by a constant nor requires any prior knowledge of the bound of uncertainty to implement the controller. A Lyapunov function‐based method has been adopted for analyzing the stability of the closed‐loop system. Simulation studies affirm the improved performance of the ARTDC in contrast to the classical artificial delay‐based methodology.

An artificial delay based robust guidance strategy for an interceptor with input saturation

This paper proposes a time-energy efficient, artificial time delay based robust guidance strategy with input saturation for a two-dimensional interceptor problem. A reference near optimal heading trajectory is generated by applying Differential Evolution (DE) to the interceptor problem. By following the reference heading trajectory, the robust control law guides the missile to intercept the target in a time-energy efficient manner, while tackling the disturbances and uncertainties that it might encounter. The near optimal trajectory is obtained offline, whereas the robust guidance strategy has been applied online which further increases the appeal of the proposed guidance scheme. Uniformly ultimately bounded (UUB) stability has been affirmed for the closed loop system employing Lyapunov’s method. Also, the proposed guidance law has been tested through simulation on both non-maneuvering and maneuvering targets performing bank to bank as well as step maneuver in the presence of uncertainties.

Fault-Tolerant Attitude Control of Small Spacecraft Using Robust Artificial Time-Delay Approach

This article presents a robust artificial time-delay-based attitude regulation control of a small spacecraft under the influence of parametric uncertainties, surrounding disturbances, and time-varying actuator faults. In the artificial time-delay (ATD) approach, the input–output information of the previous time instant is utilized to estimate the uncertain dynamical parts. The proposed attitude controller is designed by integrating the time-delay approach with a feedback control technique. Under the proposed composite control scheme, the system states are proved to be uniformly ultimately bounded (UUB) stable using the Lyapunov analysis. Moreover, the problem of unwinding in the quaternion representation, due to which the spacecraft consumes more time and energy, is also resolved under the proposed scheme. The performance of the proposed control methodology has been validated using numerical simulations. Furthermore, two different control schemes are also compared to illustrate the efficacy of the proposed strategy.

Adaptive high-order sliding mode control based on quasi-time delay estimation for uncertain robot manipulator

This paper presents the design, and validation of a new adaptive control system based on quasi-time delay estimation (QTDE) augmented with new integral second-order terminal sliding mode control (ISOTSMC) for a manipulator robot with unknown dynamic uncertainty and disturbances. Contrary to the conventional TDE, the proposed Q-TDE becomes sufficient to invoke a fixed artificial time delay and utilize the past data only of the control input to approximate the unknown system’s dynamic uncertainties. The incorporating of new adaptive reaching law with ISOTSMC augmented with Q-TDE policy ensures the continuous performance tracking of the robot manipulator’s trajectories using output feedback. This combination may achieve high performance with a significant chattering reducing procedure. By utilizing the Lyapunov function theory, it can be demonstrated that the robot system is stable and all signals in closed-loop are converging in finite time. Consequently, Simulation and comparative studies with two degrees of freedom robot manipulator were carried out to validate the effectiveness of the designed control scheme.

Memory Output-Feedback Integral Sliding Mode Control for Furuta Pendulum Systems

This paper studies the memory output-feedback integral sliding mode control for Furuta pendulum systems subject to unmatched harmonic disturbances and measurement noise. By introducing an artificial time delay, the derivatives of angular positions are approximated via Taylor’s expansion on the integral remainder. On this basis, a novel delay-dependent output-based sliding surface is constructed for state estimation and performance analysis, which inherits the appealing properties of the state-feedback integral sliding surface such as the elimination of reaching phase. Wherein, the artificial delay is regarded as a flexible design parameter ranging between 0 and its upper bound, with the bound determined by solving linear matrix inequalities. As a result, an integral sliding mode controller (ISMC) consisting of a static output-feedback part and a switching part is designed based on the descriptor system representation of the original system to control the pendulum in a noisy environment. Comparative simulation studies with $H_\infty $ control, state-feedback ISMC, and high-order ISMC demonstrate the effectiveness of the design method.

Time delay stability analysis for vibration suppression of a smart cantilever beam with hysteresis property

A stability analysis for a smart beam with an adaptive controller is presented in the paper when considering the time delay phenomenon. With the Lagrange equation and the assumed modes method, a dynamical model is constructed to describe the hysteresis nonlinearity of the smart beam. By simulation and experiment, the nonlinear model is proved effectively using the strain response near the root of the beam when the piezoelectric actuator is applied on with a chirp voltage. Based on the dynamical model, a stability analysis method is proposed with an eigenmatrix in the discrete control system. Through some simulation verifications, it is concluded that a proper time delay will be useful to improve the stability of the smart beam with an adaptive controller. Furthermore, it is verified by the experiments that the free vibration amplitude of the smart beam with an artificial time delay 0.05 s is smaller compared with that at no time delay.

Statistical test for GNSS spoofing attack detection by using multiple receivers on a rigid body

Global navigation satellite systems (GNSS) are being the target of various jamming, spoofing, and meaconing attacks. This paper proposes a new statistical test for the presence of multiple spoofers based on range measurements observed by a plurality of receivers located on a rigid body platform. The relative positions of the receivers are known, but the location and orientation of the platform are unknown. The test is based on the generalized likelihood ratio test (GLRT) paradigm and essentially performs a consistency check between the set of observed range measurements and known information about the satellite topology and the geometry of the receiver constellation. Optimal spoofing locations and optimal artificial time delays (as induced by the spoofers) are also determined.Exact evaluation of the GLRT requires the maximum-likelihood estimates of all parameters, which proves difficult. Instead, approximations based on iterative algorithms and the squared-range least squares algorithm are derived. The accuracy of these approximations is benchmarked against Cramér-Rao lower bounds.Numerical examples demonstrate the effectiveness of the proposed algorithm and show that increasing the number of GNSS receivers makes the attack easier to detect. We also show that using multiple GNSS receivers limits the availability of optimal attack positions.

H ∞ control method for seismically excited building structures with time-delay

Although remarkable studies are reported about active structural control of seismically excited building structures and different control algorithms are introduced, most of the available control strategies have neglected the effects of time-delay in the control system. However, the time-delay has a significant influence on the control performance so that instability in responses may occur if time-delay is not considered in design of controllers and their control algorithms. In this paper, two types of controllers (state feedback and dynamic output feedback controllers) are designed for vibration suppression of seismically excited building structures considering the effects of time-delay. To this aim, the dynamic differential equations of a system with an artificial time-delay are first written. Then, the dynamic system is converted into delay-free equations by using a special integral transformation. Finally, state feedback and dynamic output feedback controllers are designed by using the control theory. Simulation results show that the suggested control algorithms can effectively suppress the vibrations of building structures under time-delay conditions.

A Novel Asynchronous Control for Artificial Delayed Markovian Jump Systems via Output Feedback Sliding Mode Approach

A novel asynchronous control for a class of Markovian jump systems (MJSs) via output feedback sliding mode approach with an artificial time-delay is proposed. The asynchronous control strategy is adopted owing to the nonsynchronization between the controlled system and the controller. In some practical applications, the state variables are often difficult to be measured directly from the outside of the system, which makes the implementation of state feedback technique more complex. However, the output information is always accessible to the system. Therefore, an asynchronous output feedback sliding controller, where an artificial time-delay is introduced in the synthesis of the sliding surface, for MJSs is designed to guarantee the sliding mode dynamics satisfying the reaching condition, and a sufficient condition is derived to ensure the resultant system exponentially stable. Besides, a program of optimization is given to optimize the artificial delay-time. Finally, a numerical simulation and a practical application are given to validate the effectiveness of the proposed technique.

Adaptive sliding mode control of a class of nonlinear systems with artificial delay

In this paper, an adaptive-robust control (ARC) strategy, christened as Adaptive Time-delayed Sliding Mode Control (ATSMC) is presented for trajectory tracking control of a class of uncertain Euler-Lagrange systems. The proposed control framework brings together the best features of the switching control logic and time-delayed logic. ATSMC uses artificial time delay to approximate the unknown dynamics through time-delayed logic, and the switching logic provides robustness against the approximation error. The adaptation law for the switching gain of the conventional ARC methodologies suffer from over- and under-estimation problems. The novel adaptive law of ATSMC alleviates the over- and under-estimation problems of switching gain. Moreover, a new design methodology and stability criterion for time-delayed control is proposed which provides an upper bound on the allowable delay time. Experimental results of the proposed methodology using a nonholonomic wheeled mobile robot (WMR) is presented and improved tracking accuracy of the proposed control law is noted compared to time-delayed control and conventional adaptive sliding mode control.