Fixed-time Output Feedback Research Articles

Fixed-time output feedback stabilization for second-order switched systems with output constraints

Fixed-time output feedback stabilization for second-order switched systems with output constraints

Fixed-time trajectory tracking for autonomous surface vehicles via output feedback under various constraints

This paper proposes a novel fixed-time output feedback trajectory tracking control method suitable for autonomous surface vehicles (ASVs). Firstly, various complex uncertainty terms, such as unknown external disturbances, unmodeled errors, and actuator faults are considered in this paper. And these terms are uniformly converted into the total uncertainty terms through model transformation for convenience. Then, a fixed-time extended state observer (FTESO) with the newly expanded state is designed to observe and estimate the total uncertainty terms. Next, the saturation dynamic filter (SDF) is adopted to address the input saturation, and the saturation factors of SDF are incorporated into the trajectory error calculation to reduce the torque mutation caused by an excessive error in the control input. Finally, a fixed-time control law is proposed by taking into account the ASV system error and FTESO estimation state. Simulation experiments show that this method has excellent control performance, and this conclusion is validated through stability proof and case comparison.

Velocity-free fixed-time attitude tracking fault-tolerant control for rigid spacecraft based on the homogeneity method

This paper examines the problem of fixed-time attitude tracking fault-tolerant for rigid spacecraft without angular velocity measurement, in the presence of uncertainties, external disturbances, and actuator faults. First, a fixed-time observer is established to obtain accurate estimates of the unmeasurable angular velocities, by applying a fixed-time observer, a fixed-time tracking control method is addressed to enable the tracking spacecraft to track the target spacecraft with time-varying attitude in a fixed time. A fixed-time output feedback attitude tracking controller is designed and the fixed time stability of the system is proved. In addition, the simulation results verify the effectiveness of the proposed control strategy.

Observer-based Fixed-time Output Feedback Control for Flexible-joint Manipulators via Improved Command-filtered Backstepping

Observer-based Fixed-time Output Feedback Control for Flexible-joint Manipulators via Improved Command-filtered Backstepping

Practical fixed-time event-triggered output feedback containment control for second-order nonlinear multi-agent systems with switching topologies

This paper studies the fixed-time containment of the second-order nonlinear multi-agent system (MAS) accompanied by switching topologies and event-triggered communication. The agent is subjected to unknown nonlinear dynamics. A fixed-time RBF observer was constructed based on information obtained from neural networks and event-triggered communication. By combining the controller with the identification information from the observer, it is demonstrated that the system can achieve practical fixed-time output feedback containment and exclude Zeno behavior during the control process. The effectiveness of the proposed event-triggered control method for fixed-time output feedback containment control of the second-order nonlinear MAS is verified by simulation examples.

Adaptive Fixed-Time Output-Feedback Optimal Time-Varying Formation Control for Multiple Omnidirectional Robot Systems

Adaptive Fixed-Time Output-Feedback Optimal Time-Varying Formation Control for Multiple Omnidirectional Robot Systems

Practical fixed-time output feedback trajectory tracking control for marine surface vessels with unknown disturbances

This paper proposes a fixed-time output feedback trajectory tracking control scheme based on an extended state observer for marine surface vehicles (MSVs) with uncertain dynamics and unknown disturbances. The scheme utilizes a high-gain fixed-time extended state observer (HGFxESO) to estimate the reconstructed unmeasured velocities and lumped disturbances. The upper bound of the settling time of the HGFxESO is only determined by the design parameters, and the estimation errors can converge to a bounded set within a fixed time. Moreover, a novel fixed-time control law is proposed based on the backstepping technique and “adding a power integrator” (API) technique. The designed continuous control law ensures the trajectory tracking errors of MSVs converge to a neighborhood around the origin within a fixed time. The fixed-time stability of the MSVs trajectory tracking control system is proved using Lyapunov theory. Finally, simulation results are provided to demonstrate the effectiveness of the proposed control scheme.

Prescribed-time Closed-loop Performance Assessment: Comparative Case Study

Control loop performance assessment is addressed in the context of the output feedback stabilization in fixed-time. Existing fixed- and prescribed-time output feedback control algorithms are reviewed and their pros and cons are discussed for performing the afore-mentioned task. The control performance assessment is based on integral indices. These indices are computed from the available data obtained from numerical simulations with a simple pendulum system affected by matched disturbances and measurement noise. Simulations results corroborates the pros and cons of the fixed-time output feedback algorithms in question.

Velocity-free fixed-time output feedback attitude tracking control of rigid spacecraft

This paper studies the problem of velocity-free fixed-time attitude tracking control for spacecraft. A new fixed-time sliding mode control method is proposed for the spacecraft attitude tracking control system. And, a novel fixed-time convergent sliding surface is designed based on the fixed-time control theory. In order to estimate the unmeasurable spacecraft information, the fixed-time observer was used to estimate the attitude information of the spacecraft. Combined with the above method, the fixed-time tracking controller is developed to guarantee the attitude tracking error of spacecraft converges to a small region within a fixed time. The fixed-time stability of the closed-loop system is proved based on the Lyapunov theory, and numerical simulations are presented to illustrate the effectiveness and superiority of the controllers.

Event-Triggered Fuzzy Adaptive Fixed-Time Output-Feedback Control for Nonlinear Systems With Multiple Objective Constraints

Event-Triggered Fuzzy Adaptive Fixed-Time Output-Feedback Control for Nonlinear Systems With Multiple Objective Constraints

Fixed-time sliding mode output feedback tracking control for autonomous underwater vehicle with prescribed performance constraint

This paper studies the trajectory tracking control problem for autonomous underwater vehicles (AUVs) subject to external disturbances and model uncertainties. To improve the tracking performance of the AUVs, a prescribed performance function is introduced to constrain the output tracking error. Then, a fixed-time extended state observer (FxTESO) is set up to estimate the unknown states and the lumped disturbances (including external disturbances and model uncertainties). With the outputs of the FxTESO, a novel dynamic fixed-time terminal sliding mode (FxTTSM) surface is constructed and then a fixed-time output feedback controller is designed to achieve trajectory tracking control for the AUVs. By employing Lyapunov function theory, the stability of the closed-loop system is analyzed. Simulation results are provided to verify the effectiveness of the developed control scheme.

Practical fixed-time trajectory tracking control of constrained wheeled mobile robots with kinematic disturbances

This paper addresses the problem of practical fixed-time trajectory tracking for wheeled mobile robots (WMRs) subject to kinematic disturbances and input saturation. Firstly, considering the under-actuated characteristics of the WMR systems, the WMR model under kinematic disturbances is transformed into a two-input two-output interference system by using a set of output equations. Then, the tracking error state equation with lumped disturbances in the acceleration-level pseudo-dynamic control (ALPDC) structure is established. The lumped disturbances are estimated by a designed fixed-time extended state observer (FESO) without requiring the differentiability of the first-time derivatives of the kinematic disturbances. Meanwhile, a practical fixed-time output feedback control law is developed for trajectory tracking. By resorting to the Lyapunov stability theorem, the fixed-time stability analysis of the closed-loop WMR system in the presence of input saturation is conducted. Finally, simulation results are presented to show the effectiveness of the proposed approach.

Fixed time output feedback containment for uncertain nonlinear multiagent systems with switching communication topologies

This paper presents a fixed time containment protocol within output feedback framework for uncertain nonlinear multiagent systems (MASs) exposed to unknown leader dynamics under switching communication topologies. To characterize dynamic communication links among agents in uncertain environments, a Markov jumping process with partially known transition probability is introduced to circumvent the difficulties of requiring the exact elements of transition rates as a prior. Then, in order to eliminate the necessity of broadcasting local velocity states between neighboring agents over the wireless and reject the comprehensive uncertainties including unknown model nonlinearities, external disturbances as well as switching topology jumps, a fixed time extended state observer (FTESO) only using the relative position information as input data is established for follower agents to achieve a uniform fast and precise estimation capability. A fixed time output feedback containment protocol by means of observer is presented to ensure that individual follower is guided into the geometric area constituted by a fleet of unknown leaders with a consistent convergence time irrelevant of initial conditions. The outstanding features of the developed algorithm are threefold: First, a prescribed fixed time containment consensus with reduced communication burden and enhanced robustness can be implemented. Second, a Markov jumping process with a partially known transition probability is considered to stimulate switching communication topologies. Third, a FTESO is constructed for each agent to realize a fixed-time estimation without requiring accurate modeling information. Finally, the fixed time stabilization of cascaded system is illuminated by applying the Lyapunov-based methods and bi-limit homogeneity. Simulation examples validate the feasibility and strengths of developed control protocol.

Fixed-time output feedback sliding mode tracking control of marine surface vessels under actuator faults with disturbance cancellation

This paper proposes a novel fixed-time output feedback sliding mode tracking control of marine surface vessels (MSVs) under unknown external disturbances, unmeasurable velocities, unmodelled dynamics and actuator faults (AF). A fixed-time extended state observer (FXESO) is proposed to observe unknown lumped disturbances. Considering the FXESO, a novel fixed-time velocity-free fault-tolerant control law is applied to trajectory tracking based on a fixed-time non-singular fast terminal sliding mode manifold (FNFTSMM). The control scheme is able to make an MSV track a reference trajectory exactly, and the tracking errors can be stabilized to the origin in fixed time. Meanwhile, the upper bounded value of the convergence time does not depend on vessels’ initial values. Finally, simulation results and comparisons illustrate the merits of the proposed control scheme.

Distributed Fixed-Time Output-Feedback Attitude Consensus Control for Multiple Spacecraft

This article investigates the problem of distributed fixed-time attitude consensus control for multiple spacecraft when only a subset of spacecraft has access to a common reference attitude and angular velocity. Two fixed-time sliding-mode observers are proposed to estimate the reference attitude and angular velocity in fixed time, respectively. Based on estimates of the reference attitude and angular velocity, two distributed fixed-time attitude consensus control schemes are proposed under the mild assumption that there exists a path from the virtual leader to any follower and the communication topology among followers is undirected. In the first control scheme, the measurement of angular velocity is required. However, this requirement is removed in the second control scheme by using a fixed-time state observer to estimate the angular velocity of spacecraft in fixed time. Only a subset of spacecraft is required to access a common reference attitude and angular velocity in the two proposed control schemes. The stability and convergence of the resulting closed-loop systems are guaranteed by the Lyapunov approach. Finally, simulation results validate the effectiveness of the proposed control schemes.

Output feedback control for aircraft at high angle of attack based upon fixed-time extended state observer

This paper presents a novel fixed-time extended state observer (FXTESO)-based fixed-time output feedback control scheme for aircraft with thrust vector at high angle of attack. In order to enhance the robustness of the closed-loop control system, a FXTESO is designed to estimate and compensate model uncertainties, external disturbance and the strong coupling among different channels. Furthermore, theoretical analysis shows that the convergence time of FXTESO is independent of initial estimation errors. For the double integrator systems obtained by FXTESO feedback linearization, a continuous output feedback control is utilized to obtain expected performance and fixed-time stability. The stability analysis for the closed-loop aircraft control system is conducted by Lyapunov theory. The daisy chain method is adopted to realize the control allocation. Finally, several numerical simulations are provided to demonstrate the effectiveness and robustness of the proposed methodology.

Global Fixed-Time Output Feedback Stabilization for a Class of Double Integrator Systems

This brief deals with the problem of fixed-time output feedback stabilization for a class of stable double integrator systems. A simple output feedback nonlinear proportional-derivative (PD) control is proposed. Lyapunov stability theory and bi-limit homogeneity technique are employed to show global fixed-time stability, i.e., there exists a convergence time that is uniformly bounded a priori and such a bound is independent of the initial states. The appealing feature of the proposed control is that it is fairly easy to construct with intuitive structure and can ensure global fixed-time stability by output feedback. Simulations illustrate the improved performance of the proposed approach.

Fixed-time output feedback trajectory tracking control of marine surface vessels subject to unknown external disturbances and uncertainties

This paper proposes a novel fixed-time output feedback control scheme for trajectory tracking of marine surface vessels (MSVs) subject to unknown external disturbances and uncertainties. A fixed-time extended state observer (FESO) is proposed to estimate unknown lumped disturbances and unmeasured velocities, and the observation errors will converge to zero in fixed time. Based on the estimated values, a novel fixed-time trajectory tracking controller is designed for an MSV to track a time-varying reference trajectory by the extension of an adding a power integrator (API), and the tracking errors can converge to zero in fixed time as well. Additionally, the convergence time of the controller and the FESO is independent of initial state values. Finally, simulation results and comparisons illustrate the superiority of the proposed control scheme.

Leader-following fixed-time output feedback consensus for second-order multi-agent systems with input saturation

ABSTRACTThis paper investigates the leader-following fixed-time output feedback consensus problem for second-order multi-agent systems with input saturation. By combing fixed-time control technique and bi-limit homogeneous systems theory, a class of bounded fixed-time consensus protocols are developed for leader-following multi-agent systems. The protocol design is divided into two parts. First, when all the state information of the followers are measurable, a state feedback consensus protocol is designed to achieve fixed-time consensus. Then, when the velocity information is unmeasurable, an observer-based fixed-time consensus protocol is proposed. With the help of Lyapunov stability theorem and the property of a homogeneous function, it is theoretically shown that the states of all followers can track that of the leader in fixed-time in the presence of input saturation. Finally, numerical simulation is carried out to illustrate the effectiveness of theoretical results.

Fixed-time consensus tracking control of second-order multi-agent systems with inherent nonlinear dynamics via output feedback

This paper is devoted to the fixed-time consensus tracking control problem for a class of second-order nonlinear multi-agent systems. Firstly, a fixed-time consensus control protocol with full state feedback is proposed, which is consisted of three parts: the higher-order components for uniformly bounded convergence for any initial states, the lower-order components for exact finite time convergence to zero and the linear components for dominating the nonlinear terms in the system dynamics, respectively. By using the Lyapunov approach and bi-limit homogeneous theory, it can be proved that under the designed control protocol the fixed-time consensus tracking control can be achieved. To overcome the lack of the velocity measurements, a fixed-time convergent state observer is designed to estimate the velocity information for each agent. Then a new observer-based fixed-time output feedback control protocol is designed, which can guarantee that the states of all agents can converge to that of the leader in a fixed time. Finally, numerical simulations are performed to demonstrate the fixed-time performance of the proposed control protocol and observer.