Constant Communication Time Delay Research Articles

Observer-based adaptive force–position control for nonlinear bilateral teleoperation with time delay

In this paper, a novel observer-based force control scheme is proposed to guarantee the position and force tracking in nonlinear teleoperation systems, subject to constant communication time delay. Stability of the teleoperation system is analytically proved using the Lyapunov stability theorem. Enough condition for asymptotic convergence of the force and position are derived. The transparency is also improved by force tracking capability of the system. The teleoperation controller is then applied to a pair of planar 2-DOF robots, connected via a communication channel with constant time delay. The experimental and simulation results demonstrate the effectiveness of the proposed control algorithm, in force estimation and dealing with time delay.

Accurate proportional power sharing with minimum communication requirements for inverter-based islanded microgrids

The proportional power sharing is essential to guarantee reliability on the operation of an islanded microgrid. However, inaccurate reactive power sharing in scenarios with line impedance mismatches, and slow transient response remains important limitations of most of the conventional power sharing controllers. In this work, a novel method for power sharing control based on a decentralized Direct Current Primary Controller (DCPC) and a distributed Consensus-based Quadrature Current Controller (CQCC) is proposed. The main properties of the control approach are shown including accurate proportional active and reactive power sharing under mismatched feeder impedances and frequency regulation characteristics. Faster transient response, power sharing accuracy and minimum communication requirements are the advantages of the proposed method. The controller properties, the impact of constant communication time delays and communication failures on the power sharing performance are evaluated on different experimental study cases. These experimental results show that the accurate power sharing state is achieved in less than 2 s with frequency deviations lower than 40 mHz in all the study cases. Additionally, it is shown that the control approach tolerates constant communication time-delay of more than 200 ms and multiple communication failures that maintains the connectivity properties on the communication graph.

Adaptive control of teleoperation system based on nonlinear disturbance observer

In this paper, the problem of position tracking in the teleoperation systems subject to external forces is considered. An adaptive control algorithm and adaptive laws are proposed based on nonlinear disturbance observer in order to address the tracking error caused by external forces in the presence of constant communication time delays. First, we present a control algorithm based on the observer in the joint space for teleoperation system with uncertain dynamics; Then, to relax the assumption of identical robots, the adaptive control algorithm is extended in task space under the condition that both robots kinematic and dynamic parameters are uncertain. The stability of the proposed control algorithms incorporated with the nonlinear disturbance observer is presented based on the Lyapunov–Krasovskii criterion, and global uniform ultimate boundedness of tracking errors is achieved. Simulation results are given to validate the performance of the system utilizing the proposed controller-observer scheme.

Distributed sensor fault diagnosis for a formation system with unknown constant time delays

In this paper, a distributed velocity sensor fault diagnosis scheme is presented for a formation of a second-order multi-agent system with unknown constant communication time delays. An existing distributed proportion-derivation (DPD) formation control law is adopted and a delay-independent condition is proposed to guarantee the asymptotical formation stability of the formation system based on the Nyquist stability criterion. Then a distributed fault diagnosis scheme is developed. In each agent, a distributed fault detection residual generator (DFDRG) and a bank of distributed fault isolation residual generators (DFIRGs) are designed based on the closed-loop model of the whole system. Each DFIRG is built up on the basis of a reduced-order unknown input observer (UIO) which is robust to the fault of one neighboring agent. According to the robust relationship between DFIRGs and faults, distributed fault isolation can be achieved. Conditions are presented to guarantee that each agent is able to diagnose faults of itself and its neighbors despite the disturbance of time delays. Finally, outdoor experimental results illustrate the effectiveness of the proposed schemes.

Distributed proportion–integration–derivation formation control for second-order multi-agent systems with communication time delays

This paper considers the problem of distributed formation control for a second-order multi-agent system with a directed communication topology and constant communication time delays. A distributed proportion–integration–derivation (DPID) formation control law is proposed for the multi-agent system by introducing the integration information of the formation errors. A delay-independent condition and two delay-dependent conditions on the asymptotical formation stability are respectively presented under the assumption of the communication topology containing a directed spanning tree. Based on the Nyquist stability criterion, the range of the feasible time delays for asymptotical formation stability is obtained by analyzing the relationship between the Nyquist curves and the unit circle. Finally, simulations illustrate the effectiveness of the theoretical results.

Gain and phase margins based delay-dependent stability analysis of single-area load frequency control system with constant communication time delay

This paper presents a comprehensive stability analysis of a single-area load frequency control (LFC) system with constant communication delays. First, an exact method that takes into account both gain and phase margins is proposed to determine stability delay margins in terms of system and controller parameters. The method implements an elimination procedure to transform transcendental characteristic equation into a standard polynomial of the crossing frequency. The real roots of this new standard polynomial exactly match with the purely imaginary roots (crossing frequencies) of the original characteristic equation with transcendental terms. Secondly, an effective and simple graphical method is implemented to compute all stabilizing Proportional Integral (PI) controller gains for a given time delay. The approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space having user defined gain and phase margins, and relative stability. The time-domain simulation studies indicate that the proposed scheme improves dynamic performance gain and phase margins are included in delay-dependent stability analysis of single-area LFC with communication delays.

Comprehensive gain and phase margins based stability analysis of micro‐grid frequency control system with constant communication time delays

This study presents a comprehensive delay-dependent stability analysis of a micro-grid system with constant communication delays. First, an exact method that takes into account both gain and phase margins (GPMs) is proposed to determine stability delay margins in terms of system and controller parameters. The method implements an elimination procedure to transform transcendental characteristic equation into a standard polynomial of the crossing frequency. The real roots of this new standard polynomial exactly match with the purely imaginary roots (crossing frequencies) of the original characteristic equation with transcendental terms. Second, an effective and simple graphical method is implemented to compute all stabilising proportional integral (PI) controller gains for a given time delay. The approach is based on extracting stability region and the stability boundary locus in the PI controller parameter space having user defined GPMs, and relative stability. The time-domain simulation studies indicate that the proposed schemes give better desired dynamic performance as compared with the recently developed schemes for micro-grid with communication delays.

Decentralized Consensus Control of a Rigid-Body Spacecraft Formation with Communication Delay

The decentralized consensus control of a formation of rigid-body spacecraft is studied in the framework of geometric mechanics while accounting for a constant communication time delay between spacecraft. The relative position and attitude (relative pose) are represented on the Lie group SE(3) and the communication topology is modeled as a digraph. The consensus problem is converted into a local stabilization problem of the error dynamics associated with the Lie algebra in the form of linear time-invariant delay differential equations with a single discrete delay in the case of a circular orbit, whereas it is in the form of linear time-periodic delay differential equations in the case of an elliptic orbit, in which the stability may be assessed using infinite-dimensional Floquet theory. The proposed technique is applied to the consensus control of four spacecraft in the vicinity of a Molniya orbit.

A sliding-mode controller for dual-user teleoperation with unknown constant time delays

SUMMARYIn this paper, a control methodology is proposed for dual-user teleoperation system in the presence of unknown constant communication time delay. To satisfy dual-user system-desired objectives, three impedance characteristics are defined as the desired closed-loop system. In order to satisfy the desired impedance characteristics, a sliding-mode-based impedance controller is applied. The proposed controller affords unknown communication delay, an issue that is disregarded in the previous studies performed on dual-user systems. The nonlinear gain of the controller is achieved independent of time delay caused by communication channels. Therefore, the necessity of measurement or estimation of the time delay is relaxed. In addition, the stability analysis is presented for the closed-loop system using the passivity theory. The validity of the proposed controller scheme is demonstrated via experimental results performed on a dual-user system in the presence of unknown communication delay. In addition, due to lack of availability of forces corresponding to the operators’ hand that are required in the proposed controller, a Kalman Filter-based Force Observer (KFFO) is proposed.

一定通信遅延下におけるマルチラテラル制御系の操作性

一定通信遅延下におけるマルチラテラル制御系の操作性

PASSIVE BILATERAL CONTROL OF TELEOPERATORS UNDER CONSTANT TIME-DELAY

We propose a novel control scheme for teleoperators consisting of a pair of multi-degree-of-freedom (DOF) nonlinear robotic systems under a constant communication time delay. By passifying the communication and control blocks together, the proposed control scheme guarantees energetic passivity of the closed-loop teleoperator in the presence of parametric uncertainty and a constant communication delay without relying on widely utilized scattering or wave formalisms. The proposed control scheme also achieves master-slave position coordination and bilateral static force reflection. The proposed control scheme is symmetric in the sense that the control and communication laws of the the master and slave are of the same form. Simulations are performed to validate properties of the proposed control scheme.