Presence Of Time Delay Research Articles

CONTROL ALGORITHM OF TWO-CHANNEL FUZZY CONTROLLER FOR HEAT-ENERGY OBJECTS

Background. The reasons of control systems poor operation of complex heat and power control objects operating in changeable modes are analyzed. The peculiarity of the direct-flow steam boiler as a control object is the limited ability to conduct experimental research for identification. The incompleteness of the mathematical description does not allow fully formalizing the object for reliable design of automation systems. The temperature control circuits of the direct-flow boiler are characterized by high accumulation capacity, time delay, nonlinearity of dynamic characteristics, mutual influence of control circuits, which makes it actual to develop new control algorithms to improve the efficiency of existing control systems.Objective. The purpose is to obtain an algorithm of the control system that is insensitive to the uncertainty of the object parameters, that considers the presence of time delay through reference and disturbance channels and guarantees the given quality of regulation in changeable modes.Methods. Peculiarities of dynamic characteristics of multicapacity objects with time delays are considered. A new approach to the synthesis of fuzzy control systems is described, which addrress the adverse properties of thermal power objects, based on the experience of the operation of these facilities. Computer simulation of the synthesized control system was carried out.Results. Computer modeling confirms the rightfulness and feasibility of the proposed control algorithm. The two-channel structure of the fuzz-controller allows implementing a control method close to optimal in manual control by an experienced operator.Conclusions. With the availability of two parallel channels, the tasks for providing given quality of control system and its stability margin are delimited. The described structure of a two-channel fuzz-controller can be used to minimize the dynamic error in the initial stage of the transition process and reduce the oscillation at the final stage.

Numerical study of non-Fourier thermal ablation of benign thyroid tumor by focused ultrasound (FU)

Estimation of thermal response of tumoral tissue to the hyperthermia treatment is an important factor for increasing the effectiveness of therapeutic method. In this study, focused ultrasound (FU) is used to produce irreversible thermal damage for the treatment of benign thyroid tumor. To this end, a multi-layer model of the neck including internal organs from the skin toward the thyroid gland is exposed to ultrasound irradiation at powers of 3W, 5W, and 7W and at the frequency of 3MHz. It is observed that the acoustic pressure is noticeably increased by considering different neck's internal organs. The temperature profile is obtained by taking into account the non-Fourier thermal response for the thyroid gland. The thermal wave model and dual phase lag model are utilized along with the traditional Pennes bio-heat transfer model. Studying the temperature profile at 3W power by non-Fourier thermal models illustrates that the maximum temperature with time delays of 11.32, 5.66 and 2.86s is 20.51%, 14.1% and 8.65% lower than the corresponding value by the Fourier model. Deviation from the Fourier results is increased for higher powers of transducer. It is also inferred that in the presence of time delays, temperature variation in the focal area becomes smoother. Effect of non-Fourier heat transfer is studied on the area of necrotic tumoral region. It is concluded that region with irreversible thermal damage shrinks by considering the phase lags in the way that in 3W power and 5.66s time delay, no necrosis of the thyroid nodule is observed.

Distributed recursive filtering for discrete time-delayed stochastic nonlinear systems based on fuzzy rules

The distributed recursive filtering problem is investigated in this paper for discrete time-delayed nonlinear stochastic systems, where the well-known Takagi–Sugeno (T-S) fuzzy model is used to approximate the nonlinearities. According to obtain the system dynamics, a novel structure of distributed filters is developed, where the difference of estimated states from neighboring sensors is exploited to improve the one-step prediction, and the desired estimation is obtained by fusing the estimation under different rules. Attention is focused on the design of a distributed recursive filter such that, in the presence of time-delays and defuzzifying operations, an upper bound of the filtering error covariance is obtained and then minimized by properly designing filter parameters via elaborate mathematical analysis. With the exception of the desired gains with the online recursive form are dependent on the solutions of two Riccati-type difference equations, and the upper bound is further optimized via the introduced parameters. As a final point, a simulation examples is exploited to show the applicability of the developed filtering scheme.

Collective dynamics of globally delay-coupled complex Ginzburg-Landau oscillators.

The effect of time-delayed coupling on the collective behavior of a population of globally coupled complex Ginzburg-Landau oscillators is investigated. A detailed numerical study is carried out to study the impact of time delay on various collective states that include synchronous states, multicluster states, chaos, amplitude-mediated chimeras, and incoherent states. It is found that time delay can bring about significant changes in the dynamical properties of these states including their regions of existence and stability. In general, an increase in time delay is seen to lower the threshold value of the coupling strength for the occurrence of such states and to shift the existence domain toward more negative values of the linear dispersion parameter. Further insights into the numerical findings are provided, wherever possible, by exact equilibrium and stability analysis of these states in the presence of time delay.

Chimeras in Multiplex Networks: Interplay of Inter- and Intra-Layer Delays

Complex networks consisting of several interacting layers allow for special dynamics caused by time delay. We study the scenarios of time delay induced patterns in a three-layer network of FitzHugh-Nagumo oscillators, where each layer has a nonlocal coupling topology. Varying the time delay in the connections, we observe chimera states, i.e., complex spatio-temporal patterns of coexisting coherent and incoherent domains. In particular, we focus on the interplay of time delay in the intra-layer and inter-layer coupling term. In the parameter plane of the two delay times we find regions of existence of chimera states alternating with coherent dynamics. Moreover, in the presence of time delay we detect full and relay inter-layer synchronization.

The design of NMSS fractional-order predictive functional controller for unstable systems with time delay

Open-loop unstable systems are more difficult to control than stable processes. In presence of time delay and uncertainty, the complexity of problem increases. In this paper, non-minimal state space predictive functional control (NMSS-PFC) infrastructure has been generalized for control of unstable systems with time delay. At first, NMSS system representation has been extended for a so-called coprime-factorized equivalent model of the unstable processes. Then, the proposed NMSS-fractional-order PFC (NMSS-FOPFC) has been formulated via a fractional order cost function in terms of the output tracking error vector. In the developed formulation and via the NMSS structure, the constraints on inputs of the system could be easily formulated and employment of fractional order cost function led to improved performance even in case of disturbances, perturbations or uncertainties. Closed loop robust stability analysis was also performed based on small gain theorem and verified via simulations. Simulation examples show that the proposed NMSS-FOPFC results in improved nominal and perturbed responses compared to conventional methods. Comparison has been carried out by considering integral of absolute error (IAE) and integral of squared error (ISE) as well as step response transient and steady state properties and the control effort.

Consensus Based Control Algorithm for Nonlinear Vehicle Platoons in the Presence of Time Delay

The platoon control problem for nonlinear vehicles in the presence of time delay is investigated in this paper, where both constant time delay and time-varying delay cases are considered. A linearized third-order vehicle dynamic model is firstly derived by deploying the exact feedback linearization technique and the vehicle platoon control problem is converted into a consensus-seeking problem. Then, a consensus based vehicle platoon control algorithm with time delay is proposed, which drives vehicles to form an equally spaced platoon with the same velocity. By deploying the Lyapunov-Razumikhin theorem, the upper bound of time delay for vehicle platoon with constant time delay is derived and the sufficient conditions that guarantee the stability of the vehicle platoon are obtained. Meanwhile, the sufficient conditions that ensure the stability of vehicle platoon with time-varying delay are acquired via the Lyapunov-Krasovskii theorem. Numerical demonstrations verify the feasibility and correctness of the theoretical results.

Two-degrees-of-freedom PI[formula omitted]D controller for precise nanopositioning in the presence of hardware-induced constant time delay

The fast and accurate tracking of periodic and arbitrary reference trajectories is the principal goal in many nanopositioning applications. Flexure-based piezoelectric stack driven nanopositioners are widely employed in applications where accurate mechanical displacements at these nanometer scales are required. The performance of these nanopositioners is limited by the presence of lightly damped resonances in their dynamic response and actuator nonlinearities. Closed-loop control techniques incorporating both damping and tracking are typically used to address these limitations. However, most tracking schemes employed use a first-order integrator where a triangular trajectory commonly used in nanopositioning applications necessitates a double integral for zero-error tracking. The phase margin of the damped system combined with the hardware-induced delay deem the implementation of a double-integrator unstable. To overcome this limitation, this paper presents the design, analysis and application of a new control scheme based on the structure of the traditional Two-Degrees-of-Freedom PID controller (2DOF-PID). The proposed controller replaces the integral action of the traditional 2DOF-PID with a double integral action (2DOF-PI2D). Despite its simplicity, the proposed controller delivers superior tracking performance compared to traditional combined damping and tracking control schemes based on well-reported designs such as positive position feedback (PPF), Integral resonant control (IRC), and Positive Velocity and Position Feedback (PVPF). The stability of the control system is analyzed in the presence of a time delay in the system. Experimental results validating the efficacy of the proposed chattering-free control of a piezo-driven nanopositioning system are included.

Sliding mode control of uncertain fractional order systems with delay

ABSTRACT This paper presents a sliding mode control (SMC) based framework to design a stabilizing controller for uncertain fractional order time-delay systems (FOTDS) using the Lambert W function technique. This technique is exploited to design the fractional order (FO) sliding manifold which provides a constructive method to design an FO sliding manifold as compared to the other methods. A stabilizing switching controller is derived, that ensures the finite time reachability of the system trajectories to the sliding manifold for all subsequent time. Moreover, the conventional SMC technique can be readily applied to a particular class of FOTDS with delay free sliding mode dynamics obtained through a specific transformation. A Duffing oscillator is considered here to illustrate the proficiency of the proposed approach. Simulation results demonstrate the efficiency of the proposed method in the presence of time delay and uncertainty.

Global Hopf bifurcation of a delayed phytoplankton-zooplankton system considering toxin producing effect and delay dependent coefficient.

In this paper, a delayed phytoplankton-zooplankton system with the coeffcient depending on delay is investigated. Firstly, it gives the nonnegative and boundedness of solutions of the delay differential equations. Secondly, it gives the asymptotical stability properties of equilibria in the absence of time delay. Then in the presence of time delay, the existence of local Hopf bifurcation is discussed when the delay changes. In addition to that, the stability of periodic solution and bifurcation direction are also obtained through the use of central manifold theory. Furthermore, he global continuity of the local Hopf bifurcation is discussed by using the global Hopf bifurcation result of FDE. At last, some numerical simulations are presented to show the rationality of theoretical analyses.

Delay regulated explosive synchronization in multiplex networks

It is known that explosive synchronization (ES) in an isolated network of Kuramoto oscillators with inertia is significantly enhanced by the presence of time delay. Here we show that time delay in one layer of the multiplex network governs the transition to synchronization and ES in the other layers. We found that a single layer with time-delayed intra-layer coupling may experience a different type of transition to synchronization, e.g. ES or continuous, depending on the values of time delay. Importantly, the same type of transition is incorporated simultaneously in other layer(s) as well, irrespective of the intra-layer delay values. Hence, a suitable choice of time-delay in only one layer of a multiplex network can lead to a desired (either ES or continuous) transition simultaneously in the other layers, either directly or remotely connected to the delayed layer. These results offer a platform for a better understanding of the dynamics of those complex systems which are represented by the multilayered framework and contain time delays in the communication processes.

Online control of an active seismic system via reinforcement learning

Tuning the seismic control systems in order to achieve optimal performance is a challenging area due to the system and disturbance uncertainties. Although, model uncertainties, process time delay, and actuator dynamics can be considered as typical uncertainties, the main source of uncertainty in a seismic control system comes from the aleatory nature of earthquake disturbances. In this case, tuning of the control system based on a given seismic record may not necessarily result in optimal performance for other earthquakes. In this paper, a methodological approach is proposed for online control of active structural control systems considering seismic uncertainties. For this purpose, the concept of reinforcement learning is utilized for online tuning of an active mass drive system. The controller comprises a gain-scheduling fuzzy proportional derivative controller whose gains are tuned via an online reinforcement learning algorithm. Moreover, in order to tackle the time delays, a dynamic state predictor is utilized in conjunction with the proposed controller. To evaluate the performance of proposed controller, according to an assumed site hazard, thousand ground motion records are generated and clustered based on their spectral features using a fuzzy clustering approach. Finally, the controller is implemented in a laboratory-scale structure, and its performance is examined in the presence of the cluster centers and some real seismic records simulated on a shake table. The test results reveal successful performance of the proposed controller in tackling a wide range of seismic disturbances in the presence of time delay.

Lag projective synchronization of fractional-order delayed chaotic systems

This paper considers the lag projective synchronization of fractional-order delayed chaotic systems. The lag projective synchronization is achieved through the use of comparison principle of linear fractional equation at the presence of time delay. Some sufficient conditions are obtained via a suitable controller. The results show that the slave system can synchronize the past state of the driver up to a scaling factor. Finally, two different structural fractional order delayed chaotic systems are considered in order to examine the effectiveness of the lag projective synchronization. Feasibility of the proposed method is validated through numerical simulations.

Negotiating Corners With Teleoperated Mobile Robots With Time Delay

In this paper, we present the summary of results from a teleoperation study to assess the application of a mobile robot cornering law with the inclusion of a time delay on the returned video stream. The intent is to demonstrate this application to an analogous scenario like teleoperating from Earth a rover at the south Lunar pole. The first experiment compared course completion times for outdoor driving circuits in ideal lighting without time delay, ideal lighting with time delay, and in darkness with time delay and a low-angled spotlight. The second experiment studied cornering times for various time delays and lighting conditions in an indoor setting. The results show that teleoperating a mobile robot with the presence of time delay still complies with the previously developed cornering law. The combined results from the cornering study and the outdoor driving course are interpreted to show that the total time to complete a driving course with a time-delayed video can be predicted based on a known number of turns.

Analysis and synthesis for a class of stochastic switching systems against delayed mode switching: A framework of integrating mode weights

This paper is concerned with the issues of stability analysis and control synthesis for a class of linear stochastic switching systems in discrete-time domain. The switching dynamics are considered to be governed by a semi-Markov process and the sojourn time for each system mode is deemed to be finite. A mode-dependent control scheme is employed with an adaptation sense in the presence of time delays in the mode switching of controller, which is manifested as a constant lag between the system mode and the controller mode. A novel form of Lyapunov function is adopted, in which the Lyapunov matrix depends on the modes of both the system and the controller as well as the time since the occurrence of the last mode switching. On the basis of the new proposed σ-error mean-square stability that integrates the weights of all the system modes, numerically testable stability criteria are developed via the semi-Markov kernel approach. In virtue of certain techniques that can eliminate the terms containing powers or products of matrices, a desired mode-dependent stabilizing controller is designed such that the closed-loop system is σ-error mean-square stable by allowing a mode-unmatched controller to perform before the controller switches to a mode-matched one. Finally, the theoretical results are applied to a practical example of one joint of a space robot manipulator to demonstrate the effectiveness, applicability and superiority of the proposed control strategy as well as the necessity of considering the mode-switching delays in the designed controller.

Delay-Scheduled Controllers for Inter-Area Oscillations Considering Time Delays

Unlike the existing views that was introduced the existence of delay caused by the transmission of wide area measurement system data (WAMS) into the controllers input of the power oscilation damping (POD) by communication networks as a reason for poor performance of the POD controllers. This paper shows that the presence of time delay in the feedback loop may improve the performance of a POD controller in reducing inter-area oscilations. In fact, in a situation where the design and implementation of a POD controller for an FACT device is not easy without delays, in order to compensate for the delay effectively. In this work, a delayed scheduling method to design POD controllers is proposed. At first modeling of power system with delay as a design parameter was established. Then, the power oscillation damping delay scheduling (PODDS) based on objective function of the spectral abscissa was designed and the sufficient condition about stability of the closed-loop system is given. To evaluate the accuracy of the proposed control function and feasibility study, a four-machine power system for numerical simulation was used. The simulation results show that the controller designed in a wide range of delay changes decreases the power system oscilations without restricting SVC performance.

Observer-based H∞ finite-time controller for time-delay nonlinear one-sided Lipschitz systems with exogenous disturbances

This paper is concerned with a robust observer-based control of nonlinear one-sided Lipschitz systems in the presence of time delay, model uncertainties, and unknown energy-bounded exogenous disturbances. In this regard, firstly, an appropriate observer is designed and then a controller is achieved based on estimated state variables. Considering dynamical equations of the system together with dynamical equations of the observer error, the sufficient conditions are given for robust finite-time boundedness of the closed-loop system and satisfying the H∞ performance index. In this regard, a theorem is given and the sufficient conditions are derived in terms of feasibility testing of given linear matrix inequalities by selecting an appropriate Lyapunov–Krasovskii functional. Finally, computer simulations are performed for two examples to show the efficiency and applicability of the proposed controller.

Role of extracellular matrix and microenvironment in regulation of tumor growth and LAR-mediated invasion in glioblastoma.

The cellular dispersion and therapeutic control of glioblastoma, the most aggressive type of primary brain cancer, depends critically on the migration patterns after surgery and intracellular responses of the individual cancer cells in response to external biochemical cues in the microenvironment. Recent studies have shown that miR-451 regulates downstream molecules including AMPK/CAB39/MARK and mTOR to determine the balance between rapid proliferation and invasion in response to metabolic stress in the harsh tumor microenvironment. Surgical removal of the main tumor is inevitably followed by recurrence of the tumor due to inaccessibility of dispersed tumor cells in normal brain tissue. In order to address this complex process of cell proliferation and invasion and its response to conventional treatment, we propose a mathematical model that analyzes the intracellular dynamics of the miR-451-AMPK- mTOR-cell cycle signaling pathway within a cell. The model identifies a key mechanism underlying the molecular switches between proliferative phase and migratory phase in response to metabolic stress in response to fluctuating glucose levels. We show how up- or down-regulation of components in these pathways affects the key cellular decision to infiltrate or proliferate in a complex microenvironment in the absence and presence of time delays and stochastic noise. Glycosylated chondroitin sulfate proteoglycans (CSPGs), a major component of the extracellular matrix (ECM) in the brain, contribute to the physical structure of the local brain microenvironment but also induce or inhibit glioma invasion by regulating the dynamics of the CSPG receptor LAR as well as the spatiotemporal activation status of resident astrocytes and tumor-associated microglia. Using a multi-scale mathematical model, we investigate a CSPG-induced switch between invasive and non-invasive tumors through the coordination of ECM-cell adhesion and dynamic changes in stromal cells. We show that the CSPG-rich microenvironment is associated with non-invasive tumor lesions through LAR-CSGAG binding while the absence of glycosylated CSPGs induce the critical glioma invasion. We illustrate how high molecular weight CSPGs can regulate the exodus of local reactive astrocytes from the main tumor lesion, leading to encapsulation of non-invasive tumor and inhibition of tumor invasion. These different CSPG conditions also change the spatial profiles of ramified and activated microglia. The complex distribution of CSPGs in the tumor microenvironment can determine the nonlinear invasion behaviors of glioma cells, which suggests the need for careful therapeutic strategies.

High-Performance Adaptive Pressure Control in the Presence of Time Delays: Pressure Control for Use in Variable-Thrust Rocket Development

Smart defense systems using missiles that can fine-tune their velocity profiles have significant technological superiority over their conventional counterparts. This tuning is possible, in part, due to the deployment of advanced sensing, actuation, and computation capabilities and sophisticated guidance, navigation, and control algorithms. The capability to alter velocity during operation helps sustain optimum performance for different flight conditions. In addition, it makes it possible to slow down while turning and then speed up along a straight path, rendering the maneuvers more efficient. This ability to modify velocity (known as throttleability) is also known to increase a missile's no-escape zone, which is the maximum range that the missile can outrun its target [1]. As presented in Summary, this article discusses the advanced control technologies needed to obtain throttleability.

Distributed Integer Weight Balancing in the Presence of Time Delays in Directed Graphs

A digraph with positive weights on its edges is weight-balanced if, for each node, the sum of the weights of the incoming edges is equal to the sum of the weights of the outgoing edges. Weight-balanced digraphs play an important role in a variety of cooperative control problems, including formation control, event-triggered coordination, distributed averaging, and optimization. Classical distributed algorithms for asymptotic average consensus typically assume timely and reliable exchange of information between neighboring components of a given multicomponent system. These assumptions are not necessarily valid in practice due to varying delays that might affect computations at different nodes and/or transmissions at different links. In this paper, we propose a distributed algorithm that solves the integer weight balancing problem in the presence of arbitrary (time-varying and inhomogeneous) time delays that might affect the transmission at a particular link at a particular time. The algorithm converges after a finite number of steps (that we explicitly bound) in the presence of bounded delays and converges in finite time (with probability one) in the case of unbounded delays (packet drops). Furthermore, we show that the resulting weight-balanced digraph is unique regardless of how time delays or packet drops manifest themselves. We also analyze the computational and communication complexity of the proposed algorithm, and provide examples to illustrate its operation and performance.