Variable Communication Delays Research Articles

Distributed secondary frequency control scheme with A-symmetric time varying communication delays and switching topology

A distributed control of a Microgrid (MG) depends on the communication network for the exchange of information among the Distributed Generators (DGs). Most of the control schemes consider ideal communication among the DGs; however, in practical systems, delays are inherited in a system that can affect the dynamic performance and even destabilize an MG. Therefore, in this research work, delay independent distributed secondary frequency control for MGs is presented. Sufficient delay independent conditions for robust stability of the buffer-free Distributed Averaging Integral (DAI) control scheme is proposed while considering A-symmetric time varying communication delays and switching network topology. Moreover, in this work, slow as well as fast varying delays are analyzed using Lyapunov Krasovskii and Lyapunov Razumikhin's approach. Furthermore, a Lyapunov function based adaptive control approach is employed that updates the constant gain parameters to compensate for the uncertain or varying parameters. Finally, the efficacy of the controller is demonstrated through simulation studies that validate its performance in different scenarios.

Enhancement of virtual inertia via delay designed GADRC in hybrid microgrid with communication delay

The lowering of inertia in a hybrid microgrid caused by the incorporation of renewable sources of energy leads to an increased rate of change of frequency and frequency deviation in the system. Further, the varying load demand and the presence of communication delay adversely affect the frequency regulation. In view of this, in this paper, a modified virtual inertia control strategy is formulated and implemented through the energy storage device to enhance the overall inertia of the hybrid microgrid. Secondly, a delay-designed generalized active disturbance rejection control (DD-GADRC) technique is proposed for the secondary frequency control of the power system under varying communication delay and rapidly fluctuating load demand in the system. The effectiveness of the proposed control scheme is evaluated across multiple scenarios, including situations when there are continuous changes in solar or wind power generations. The robustness of the proposed technique is also evaluated under parametric variations and the presence of non-linearities in the system. Finally, the effectiveness of the proposed technique is analyzed and compared to various pre-existing control strategies in the literature related to the hybrid microgrid.

Distributed Hybrid Control for Heterogeneous Multiagent Systems With Variable Communication Delays and Its Application to DC Microgrids

Distributed Hybrid Control for Heterogeneous Multiagent Systems With Variable Communication Delays and Its Application to DC Microgrids

A Novel Adaptive Finite-Time Position Tracking Control Strategy for Teleoperation System with Varying Communication Delays

Based on the traditional control approach, the position-tracking performance of the teleoperation system with communication delay is generally asymptotically stable. In practical applications, the closed-loop system is expected to achieve stable and finite-time convergence performance. A novel finite-time bilateral control scheme for a telerobotics system with communication delay is presented in this paper. On the basis of the traditional proportional damping injection control, this paper proposes and designs a new finite-time control method by introducing the non-integer power to the position error, velocity, and the combined error with position error and velocity. In comparison to existing proportional damping injection and finite-time control structures, the proposed method not only achieves the finite-time convergence performance of position tracking, but it also has the advantages of a simple structure and fewer gain coefficients. The controller also incorporates the radial basis function (RBF) neural network and adaptive approach to compensate unknown dynamics and external forces, thus also avoiding the measurement of force signals. The Lyapunov–Krasovskii function is then defined, and it is demonstrated that the position tracking of closed-loop teleoperation system has bounded stability and finite-time control performance. The simulation experiment is also performed, and the results further illustrated the bounded stability of the system. Moreover, compared to the position tracking errors of other non-finite-time control methods, it is demonstrated that the proposed finite-time control scheme has a faster convergence rate and higher convergence precision.

Multi-Stage NMPC for a MAV based Collision Free Navigation Under Varying Communication Delays

Time delays in communication networks are one of the main concerns in deploying robots with computation boards on the edge. This article proposes a multi-stage Nonlinear Model Predictive Control (NMPC) that is capable of handling varying network-induced time delays for establishing a control framework being able to guarantee collision-free Micro Aerial Vehicles (MAVs) navigation. This study introduces a novel approach that considers different sampling times by a tree of discretization scenarios contrary to the existing typical multi-stage NMPC where system uncertainties are modeled by a tree of scenarios. Additionally, the proposed method considers adaptive weights for the multi-stage NMPC scenarios based on the probability of time delays in the communication link. As a result of the multi-stage NMPC, the obtained optimal control action is valid for multiple sampling times. Finally, the overall effectiveness of the proposed novel control framework is demonstrated in various tests and different simulation environments.

Transmission line modeling co-simulation with distributed delay-size control using steady-state identification

Combining performance and numerical stability is a key issue in co-simulation. The Transmission Line Modeling method uses physically motivated communication delays to ensure numerical stability for stiff connections. However, using a fixed communication delay may limit performance for some models. This paper proposes Steady-State Identification for enabling variable communication delays. Three algorithms for online Steady-State Identification are evaluated in three different co-simulation models. All algorithms are able to identify steady state and can thereby determine when communication delays can be allowed to increase without compromising accuracy and stability. The results show a reduction in number of the solver derivative evaluations by roughly 40–60% depending on the model. The proposed method additionally supports connections with asymmetric communication delays, which allows each sub-model to independently control the delay of its input variables. Models supporting delay-size control can thereby be connected to those that do not, so that the step length of each individual sub-model is maximized. Controlling the delay-size in sub-models also makes the method independent of the master co-simulation algorithm.

Adaptive control for position and force tracking of uncertain teleoperation with actuators saturation and asymmetric varying time delays

Abstract This paper presents a new bounded force feedback control law to improve transparency in nonlinear bilateral teleoperation systems in the presence of three problems in practical applications of teleoperation systems such as input saturation, asymmetric time varying communication delays with no restriction on their rates of variation and parametric uncertainties, simultaneously. The proposed controller is a nonlinear-proportional plus nonlinear damping (nP + nD) controller with the addition of a nonlinear adaptive term and nonlinear function of the environment force on the slave side and nonlinear function of the human force and force error on the master side. Using a novel Lyapunov–Krasovskii functional, the asymptotic stability and position and force tracking performance of the teleoperation system are established under specific conditions on the controller parameters, actuator saturation characteristics and maximum allowable time delay. The validity of the theoretical results is corroborated by the simulation results.

Design of Improved Nonlinear Active Disturbance Rejection Controller for Hybrid Microgrid With Communication Delay

In this paper, an improved nonlinear active disturbance rejection control (INLADRC) approach is proposed for load frequency control of hybrid microgrid with communication delay. The INLADRC technique includes a nonlinear extended state observer (NESO) to estimate the system states and a nonlinear controller for the cancellation of the generalized disturbance acting on system. The effect of communication delay in the hybrid microgrid system is alleviated via the incorporation of an auxiliary structure that also restores the synchronization between the inputs of NESO. The efficacy of the proposed approach is validated via a comprehensive analysis, wherein step variations as well as random perturbations are considered in solar power, wind power and load demand. Further, the performance of proposed technique is also corroborated via consideration of real time solar and wind data. Moreover, the robustness of INLADRC technique is investigated in presence of parametric uncertainty, model-plant mismatch, delay time mismatch as well as varying communication delay. An extensive comparative analysis is a testimony to the effectiveness of INLADRC approach.

Design of fractional order PID controller for load frequency control system with communication delay

This work explores a frequency-domain approach to design a fractional order proportional–integral–derivative (FO-PID) controller cascaded with a first-order filter for the load frequency control (LFC) system with communication delay. The proposed method is based on suitable reference model development in the direct synthesis (DS) approach, followed by frequency response matching technique. The reference model is developed for robust control-loop performance using the stability-margin and time-domain specifications. The values of the fractional orders of the integral and derivative terms are obtained according to the dynamics of the nominal system. The proposed controllers have been designed for some LFC systems taken from the literature that have different dynamics with reheat, non-reheat and hydraulic turbines and performances with non-linearity like generation rate constraint (GRC), generation dead band (GDB) along with noise have been compared favorably with that of some controllers prevalent in the literature. The proposed controllers have been shown to work efficaciously for the decentralized multi-area IEEE 39-bus New England test system along with variable communication delay. To show the efficacy of the proposed controllers the load-disturbance responses along with the frequency and time domain performance indices have been evaluated for comparison.

Generalized active disturbance rejection controller design: Application to hybrid microgrid with communication delay

In this paper, generalized active disturbance rejection control (GADRC) technique in the presence of communication delay is proposed for load frequency control of a hybrid microgrid system, which is composed of renewable energy sources such as solar and wind input, energy storage devices such as battery energy storage system and flywheel energy storage system as well as fuel cell and diesel generator which are controllable sources of energy. The presence of communication delay involved in transmission of control signals is also considered for controller design. Further, the robustness of proposed scheme is investigated via an elaborate study comprising of varying communication delay, parametric uncertainty, nonlinearities such as generation rate constraint and governor deadband, as well as mismatch in communication delay between the inputs of observer. Finally, the performance indices of the proposed scheme are compared with conventional and fractional order based controller design approaches. The simulation results are a testimony to the efficacy of proposed scheme.

A Consensus Control for a Multi-Agent System With Unknown Time-Varying Communication Delays

A multi-agent system to have information flow among agents is bound to experience a communication delay over a directed graph. However, delay information is often unavailable and time varying. To deal with this problem, a consensus control for a second-order multi-agent system consisting of a leader and multiple followers is developed. Sliding mode control is exploited to deal with uncertainties incurred by unknown time varying communication delay and disturbance. The proposed sliding mode consensus control is shown to achieve the asymptotic bounded consensus and the finite time convergence of a sliding variable for any unknown time varying delay with the bounded first and the second derivative. The numerical simulations verify the properties of the proposed algorithm and its performance which is almost identical to one achieved by a consensus algorithm exploiting known delay information.

Robust Time-Delay Feedback Control of Vehicular CACC Systems with Uncertain Dynamics.

This paper proposes a new, robust time-delay cooperative adaptive cruise control (CACC) approach for vehicle platooning systems with uncertain dynamics and varying communication delay. The uncertain CACC models with perturbed parameters are used to describe the uncertain dynamics of the vehicle platooning system. By combining the constant time headway strategy and predecessor-following communication topology, a set of robust delay feedback controllers is designed for the uncertain vehicle platoon with varying communication delay. Then, the set of CACC controllers is computed by solving some linear matrix inequalities, which further establish the robust (string) stability of the uncertain platooning system with the varying communication delay. The co-simulation experiment of CarSim and Simulink with a group of a seven-car platoons and varying velocity is used to demonstrate the effectiveness of the presented method.

Formation Control of Multiple Autonomous Underwater Vehicles Under Communication Delays

Time-delay owing to the communication delay in acoustic modem greatly influences the path following performances when a group of Autonomous Underwater Vehicles (AUVs) are deployed in formation. When the AUVs are employed in oceanic environment, the distance between the AUVs keeps on changing due to wave disturbances. Hence, time-delay which depends on the distance between AUVs also varies. In this brief, a time-delay estimator based on gradient-descent method has been designed to estimate the communication delays. Taking the estimated delay into account, the delayed error vectors are computed to design a suitable control input. As the reduction of Lyapunov function incorporating communication delay occurs on-line at each sampling interval, the path following control performance of follower AUV improves significantly. The simulation and experimental results show that the delay estimator accurately estimates the delay. Moreover, during experiment, the actual delay is significantly reduced as the time-stamping of packets of leader AUV states is avoided during formulation of the estimator. The follower AUV even under the effects of variable communication delay, maintains a desired distance from the leader AUV. The results also show that by imposing constraints on the control input, actuator saturation is avoided.

Decentralized Dynamic Event-Triggered $\mathcal {H}_{\infty }$ Control for Nonlinear Systems With Unreliable Communication Channel and Limited Bandwidth

This article investigates the dynamic event-triggered $\mathcal {H}_{\infty }$ control problem for nonlinear networked control systems with unreliable communication channel, variable communication delays, and limited bandwidth. The nonlinear plant is represented by discrete-time polynomial fuzzy model. First, a decentralized dynamic event-triggered mechanism is proposed to determine whether the measured data are transmitted or not, and in order to exclude data collision caused by limited bandwidth, novel try-once-discard and flexible round-robin scheduling protocols are proposed to assign communication channel to certain sensor node. Then, Bernoulli distribution is employed to model the unreliable communication channel, and a new random sequence is developed to model the received data sequence under the effect of data losses and scheduling protocols. Furthermore, a discrete-time stochastic system model with both state and error delays is constructed, and sufficient conditions in the form of sum-of-squares are developed for the design of $\mathcal {H}_{\infty }$ controllers such that the closed-loop system is stochastically stable and preserves guaranteed $\mathcal {H}_{\infty }$ performance. Finally, two simulation examples are provided to illustrate the effectiveness of the proposed results.

Robust Interval Type-2 Fuzzy Observer for Fault Detection of Networked Control Systems Subject to Immeasurable Premise Variables

In this paper, a novel observer design has been suggested for fault detection of networked control systems under random measurement delays. A randomly varying communication delay structure has been assumed in data transmission between the physical system and the observer. In order to increase the applicability of the proposed Takagi-Sugeno fuzzy observer, it has been contemplated to be under immeasurable premise variables. In addition, time-varying parameter uncertainties are added to the system, which contribute to the system uncertainties. Theoretical materials related to the system and the observer design with a predetermined H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> index are provided resulting in less conservative constraints in the proof of asymptotical mean-square stability of the closed-loop system. Simulation results, which have been applied to a real-world system of tunnel diode circuit, have shown how the proposed observer would benefit from the use of interval type-2 fuzzy sets in dealing with uncertainties of the system.

Symbolic Abstractions of Networked Control Systems

The last decade has witnessed significant attention on networked control systems (NCSs) due to their ubiquitous presence in industrial applications, and in the particular case of wireless NCSs, because of their architectural flexibility and low installation and maintenance costs. In wireless NCSs, the communication between sensors, controllers, and actuators is supported by a communication channel that is likely to introduce variable communication delays, packet losses, limited bandwidth, and other practical nonidealities leading to numerous technical challenges. Although stability properties of NCSs have been investigated extensively in the literature, results for NCSs under more complex and general objectives, and, in particular, results dealing with verification or controller synthesis for logical specifications, are much more limited. This paper investigates how to address such complex objectives by constructively deriving symbolic models of NCSs, while encompassing the mentioned network nonidealities. The obtained abstracted (symbolic) models can then be employed to synthesize hybrid controllers enforcing rich logical specifications over the concrete NCS models. Examples of such general specifications include properties expressed as formulas in linear temporal logic or as automata on infinite strings. We thus provide a general synthesis framework that can be flexibly adapted to a number of NCS setups. We illustrate the effectiveness of the results over some case studies.

Output Feedback Consensus of Nonlinear Multi-Agent Systems under a Directed Network with a Time Varying Communication Delay

Output Feedback Consensus of Nonlinear Multi-Agent Systems under a Directed Network with a Time Varying Communication Delay

Robust output feedback distributed model predictive control of networked systems with communication delays in the presence of disturbance

In this work, an output feedback cooperative distributed model predictive control is developed for a class of networked systems composed of interacting subsystems interconnected through their states, in which it handles bounded disturbances and time varying communication delays. A distributed buffer based prediction strategy is used to compensate bounded delays and predict those states, which are coupled between subsystems that their actual values may not available due to delays. In the design of robust distributed model predictive control, distributed moving horizon estimation is employed so that convergence and boundedness of the estimation error are ensured. Furthermore, robust exponential stability of the closed loop system is established. The effectiveness of the proposed method is illustrated using two interconnected continuous stirred tank reactors.

Stabilization of Networked Control Systems Under Clock Offsets and Quantization

This paper studies the impact of clock mismatches and quantization on networked control systems. We consider a scenario where the plant's state is measured by a sensor that communicates with the controller through a network. Variable communication delays and clock jitter do not permit a perfect synchronization between the clocks of the sensor and controller. We investigate limitations on the clock offset tolerable for stabilization of the feedback system. For a process with a scalar-valued state, we show that there exists a tight bound on the offset above which the closed-loop system cannot be stabilized with any causal controllers. For higher dimensional plants, if the plant has two distinct poles, then the effect of clock mismatches can be canceled with a finite number of measurements, and hence there is no fundamental limitation. We also consider the case where the measurements are subject to quantization in addition to clock mismatches. For first-order plants, we present necessary conditions and sufficient conditions for stabilizability, which show that a larger clock offset requires a finer quantization.

Resilient control design for consensus of nonlinear multi-agent systems with switching topology and randomly varying communication delays

This paper examines the robust consensus problem of nonlinear multi-agent systems via a resilient controller subject to switching topology, wherein the effect of uncertainty in the form of additive perturbations and a randomly varying communication delay is considered in the control design. In particular, a directed graph is used to describe the interaction topology of the addressed multi-agent system and a stochastic variable obeying the Bernoulli distributed white sequences is incorporated to represent the randomness of delay. By utilizing the Lyapunov’s direct method and some matrix operations, a sufficient condition for mean-square asymptotic consensus of the addressed system is derived. Subsequently, the explicit characterization of the resilient control gain is obtained by means of linear matrix inequalities that can be effectively solved by using the ideas of convex optimization. An academic example is eventually presented to illustrate the significance and potency of the proposed control design strategy.