Zongyu Zuo

Nonsingular fixed-time consensus tracking for second-order multi-agent networks

This paper investigates the fixed-time consensus tracking problem for second-order multi-agent systems in networks with directed topology. Global well-defined nonlinear consensus protocols are constructed with the aid of a newly-designed sliding surface for each double-integrator agent dynamics. In particular, the proposed framework eliminates the singularity and the settling time is assignable for any initial conditions. This makes it possible for network consensus problems to design and estimate the convergence time off-line. Finally, simulation is included to demonstrate the performance of the new protocols.

A new class of finite-time nonlinear consensus protocols for multi-agent systems

This paper is devoted to investigating the finite-time consensus problem for a multi-agent system in networks with undirected topology. A new class of global continuous time-invariant consensus protocols is constructed for each single-integrator agent dynamics with the aid of Lyapunov functions. In particular, it is shown that the settling time of the proposed new class of finite-time consensus protocols is upper bounded for arbitrary initial conditions. This makes it possible for network consensus problems that the convergence time is designed and estimated offline for a given undirected information flow and a group volume of agents. Finally, a numerical simulation example is presented as a proof of concept.

Distributed robust finite-time nonlinear consensus protocols for multi-agent systems

This paper investigates the robust finite-time consensus problem of multi-agent systems in networks with undirected topology. Global nonlinear consensus protocols augmented with a variable structure are constructed with the aid of Lyapunov functions for each single-integrator agent dynamics in the presence of external disturbances. In particular, it is shown that the finite settling time of the proposed general framework for robust consensus design is upper bounded for any initial condition. This makes it possible for network consensus problems to design and estimate the convergence time offline for a multi-agent team with a given undirected information flow. Finally, simulation results are presented to demonstrate the performance and effectiveness of our finite-time protocols.

Adaptive trajectory tracking control design with command filtered compensation for a quadrotor

The design of a flight controller capable of not only stabilizing attitude but also tracking a trajectory accurately for a quadrotor aircraft in presence of parametric uncertainties and external disturbances is more challenging than that in the absence of uncertainties. In this paper we propose an adaptive trajectory tracking control algorithm, based on the relationship between attitude and linear acceleration, using online adaptive approximator to estimate unknown aerodynamic parameters and external disturbance upper bounds, and a linear tracking-differentiator to eliminate the timescale separation assumption between attitude and linear dynamics in control system design. The stability of the closed-loop control system is proven subsequently. Finally, the validity and the improvement of this proposed algorithm relative to the previous work are demonstrated through numerical simulations of tracking a circular trajectory under several conditions, including basic parametric uncertainty, exogenous wind disturbance and control input oscillation eliminating via a hyperbolic tangent function instead of a sign function.

Augmented L 1 adaptive tracking control of quad-rotor unmanned aircrafts

This paper addresses a new trajectory tracking controller for quad-rotor aircrafts in the presence of time-varying aerodynamic effect and bounded external disturbance using the novel L1 adaptive control methodology augmented with nonlinear feed-forward compensations. The proposed augmented L1 adaptive controller achieves uniformly bounded transient and asymptotic tracking of the output signal for any designated bounded reference trajectory. Finally, simulations of tracking a circular reference trajectory are performed to illustrate the validity of the proposed controller.

Robust Three-Loop Trajectory Tracking Control for Quadrotors With Multiple Uncertainties

In this paper, a robust decentralized and linear time-invariant controller is proposed for quadrotors to achieve trajectory tracking. The designed closed-loop control system includes three loops: (1) an attitude loop that controls the attitude angles; (2) a position loop that controls the translational trajectory of the quadrotor; and (3) a robust compensating loop that restrains the influence of uncertainties including parameter uncertainties, nonlinear and coupling dynamics, and external disturbances in the rotational and translational dynamics. It is proven that the tracking errors can converge into a priori set neighborhood of the origin ultimately. Experimental results are given to confirm the advantages of the proposed control method, compared with the linear time-invariant H∞ control method.

Consensus Control of a Class of Lipschitz Nonlinear Systems With Input Delay

This paper deals with the consensus control design for Lipschitz nonlinear multi-agent systems with input delay. The Artstein-Kwon-Pearson reduction method is employed to deal with the input delay and the integral term that remains in the transformed system is analyzed by using Krasovskii functional. Upon exploring certain features of the Laplacian matrix, sufficient conditions for global stability of the consensus control are identified using Lyapunov method in the time domain. The proposed control only uses relative state information of the agents. The effectiveness of the proposed control design is demonstrated through a simulation study.

A fixed-time output feedback control scheme for double integrator systems ☆

Abstract A continuous output feedback control scheme rendering the closed-loop double integrator system globally stable in finite-time is presented. In particular, the convergence time is independent of initial conditions. The bi-limit homogeneous technique is used for controller and observer designs with fixed-time convergence. Then, a continuous output feedback control law is proposed for nominal double-integrator system and its perturbed version. The homogeneity and Lyapunov techniques are used to ensure the fixed-time stability of the closed-loop system under output feedback control framework. Finally, the efficiency of the proposed algorithms is illustrated by numerical simulations.

Backstepping Control for Gear Transmission Servo Systems With Backlash Nonlinearity

The output tracking problem of gear transmission servo (GTS) systems with backlash nonlinearity is studied in this paper. A new concept-“soft degree”-is proposed to overcome the nondifferentiable “hard” characteristic of the backlash nonlinearity. Furthermore, a detailed softening process-static softening is presented, where a backstepping control algorithm is developed to guarantee that the output of the controlled systems can track any given desired sufficiently smooth trajectory by arbitrary precision and the limit cycles that appear due to backlash nonlinearity can be avoided. Simulation results validate the effectiveness of the proposed controller.

Robust Control for Quadrotors With Multiple Time-Varying Uncertainties and Delays

Robust trajectory tracking control problem is dealt with for quadrotors with multiple uncertainties and multiple delays. The vehicle model is described as a multiple-input multiple-out time-varying system subject to parametric perturbations, nonlinear and coupled dynamics, external disturbances, and state and input delays. A robust cascade controller including an attitude controller and a position controller is proposed based on the hierarchical control scheme and the robust compensating technique. It is proven that the position and attitude tracking errors can converge into the given neighbourhood of the origin in a finite time, subject to multiple uncertainties and delays. Experimental results on the quadrotor system are provided to verify the effectiveness of the proposed controller.