一类连续级联系统的全局一致稳定性

针对一类非线性连续级联系统, 利用齐次系统的齐次性质给出了其全局一致稳定性分析结果. 假设级联系统中的驱动子系统和被驱动子系统分别满足全局一致渐近稳定且满足一定的齐次度, 若级联项也满足一给定齐次不等式, 则整个非线性级联系统为全局一致渐近稳定的. 若驱动子系统和被驱动子系统都具有负的齐次度, 则该非线性级联系统为全局一致有限时间稳定的. 与传统的ISS假设或级联项增长假设相比, 文中方法所给的齐次不等式条件更容易验证. 且文中方法不仅适用于Lipschitz连续的系统, 而且适用于非Lipschitz连续的系统. 两个例子验证了该方法的有效性.     

一类二阶非线性系统的有限时间状态反馈镇定方法

针对一类二阶非线性系统的有限时间状态反馈镇定问题进行了讨论. 给出了三种基于连续状态反馈的全局有限时间状态反馈镇定方法. 首先，利用非线性齐次系统性质，设计出一种状态反馈控制器，使得闭环系统渐近稳定并且具有负的齐次度；其次，基于有限时间Lyapunov函数的反步构造法，给出了一种有限时间控制器；最后，利用非奇异终端滑模控制技术，得到了一种使闭环系统有限时间收敛到平衡点的反馈镇定控制器. 仿真结果表明了这些方法的有效性.     

Global uniform asymptotical stability of a class of nonlinear cascaded systems with application to a nonholonomic wheeled mobile robot

In this article, we consider the stability analysis problem for a class of nonlinear cascaded systems by using homogeneous properties. Assume that the driving subsystem and the driven subsystem are both homogeneous and locally uniformly asymptotically stable. If the cascaded term satisfies a given inequality, then the cascaded system is globally uniformly asymptotically stable. Furthermore, in the case that both degrees of homogeneity are negative, the cascaded system is globally uniformly finite-time stable. Compared with the existing methods, the conditions given in this article are much easier to verify. These stability results are applied to the global tracking control problem of a nonholonomic wheeled mobile robot. Simulation results are provided to show the effectiveness of the methods.     

Semi-global finite-time observers for nonlinear systems

It is well known that high gain observers exist for single output nonlinear systems that are uniformly observable and globally Lipschitzian. Under the same conditions, we show that these systems admit semi-global and finite-time converging observers. This is achieved with a derivation of a new sufficient condition for local finite-time stability, in conjunction with applications of geometric homogeneity and Lyapunov theories.     

Adaptive finite-time consensus in multi-agent networks

This paper is concerned with the finite-time consensus problem of distributed agents having non-identical unknown nonlinear dynamics, to a leader agent that also has unknown nonlinear control input signal. By parameterization of unknown nonlinear dynamics, a Lyapunov technique in conjunction with homogeneity technique is presented for designing a decentralized adaptive finite-time consensus control protocol in undirected networks. Homogeneous Lyapunov functions and homogeneous vector fields are introduced in the stability analysis although the whole system is not homogeneous. Theoretical analysis shows that leader-following consensus can be achieved in finite-time, meanwhile, finite-time parameter convergence can be also guaranteed under the proposed control scheme. An example is given to validate the theoretical results.     

Finite-time stability analysis of impulsive discrete-time switched systems with nonlinear perturbation

The problem of finite-time stability for a class of discrete-time switched systems in the presence of both non-Lipschitz perturbation and impulse effects is studied in this paper. Based on the average dwell-time approach, a criterion is proposed which ensures that the system’s state trajectory remains in a bounded region of the state space over a pre-specified finite-time interval if we impose a bound on the initial condition. It is shown that the finite-time stability degree could be greater than one, which is quite different from the existing results for asymptotic stability. Moreover, the total activation time of the Schur stable subsystems does not need to be greater than that of the unstable subsystems. A numerical example is presented to illustrate the effectiveness of the proposed design method.     

切换非线性正系统的有限时间稳定性

研究模型依赖平均驻留时间(MDADT)切换信号下一类齐次度为1的切换非线性正系统的有限时间稳定问题.首先,通过构造恰当的切换最大分离Lyapunov函数,借助于Dini导数,基于MDADT切换信号,给出切换非线性正系统有限时间稳定的充分条件.与已有的指数稳定性结果相比,进一步说明有限时间稳定与指数稳定的区别.其次,将所得结论应用于切换线性正系统,得到切换线性正系统在MDADT或平均驻留时间(ADT)切换信号下有限时间稳定的充分条件.最后,通过仿真算例验证所得结论的有效性.     

Finite-time formation of multiple agents based on multiple virtual leaders

The finite-time formation problem of multiple agents aims to find a control protocol to guarantee finite-time consensus, in which every agent can be in the right position and keep in the given formation configuration efficiently. However, it is hard to achieve a stable state if only by setting one virtual leader in multiple tasks system. This paper presents a formation controller design for a second-order multiple agents to address the finite-time formation problem. In the procedure, each agent has a virtual leader, and then a control law is designed so that the agents can keep pace with their virtual leaders in terms of speed and position. Accordingly, the controller can ensure that the relative positions among different agents and the trajectory of the whole formation can be specified in advance. Moreover, since the closed-loop system is finite-time stable, which implies that the required formation is attainable without a deviation in finite time. Finally, the stability analysis is proved by applying the graph theory, Lyapunov stability theory and homogeneous system theory. The effectiveness of the algorithm is demonstrated by numerical simulations.     

PID control for global finite-time regulation of robotic manipulators

This paper addresses the global finite-time regulation problem of robotic manipulators. A simple nonlinear proportional-integral-derivative (PID) control is proposed by adding a nonlinear proportional and derivative term to the commonly used PID controller. Lyapunov's stability theory and geometric homogeneity technique are employed to prove global finite-time stability. Advantages of the proposed control include the absence of modelling information in the control law formulation and the global finite-time stability featuring fast transient and high-precision positioning. Explicit conditions on the controller parameters to ensure global finite-time regulation stability are obtained. Simulations are presented to demonstrate the effectiveness and the improved performances of the proposed approach.     

Finite-Time Observers: Application to Secure Communication

In this paper, control theory is used to formalize finite-time chaos synchronization as a nonlinear finite-time observer design issue. This paper introduces a finite-time observer for nonlinear systems that can be put into a linear canonical form up to an output injection. The finite-time convergence relies on the homogeneity properties of nonlinear systems. The observer is then applied to the problem of secure data transmission based on the finite-time chaos synchronization and the two-channel transmission method.      

Finite-time output feedback stabilisation for a class of feedforward nonlinear systems with input saturation

This paper considers the problem of global finite-time stabilisation by output feedback for a class of feedforward (upper triangular) nonlinear systems with input saturation. Based on the finite-time stability theorem, and by skillfully using the homogeneous domination approach and the nested saturation technique, a saturated output feedback controller is successfully constructed, which renders the origin of the closed-loop system globally finite-time stable. In simulation studies, a numerical example is illustrated to show the effectiveness of the control scheme. Moreover, the design strategy is successfully applied to solve the saturated finite-time control problem for vertical wheel on rotating table.     

Finite-time consensus for multi-agent networks with unknown inherent nonlinear dynamics

The objective of this paper is to analyze the finite-time convergence of a nonlinear but continuous consensus algorithm for multi-agent networks with unknown inherent nonlinear dynamics. Due to the existence of the unknown inherent nonlinear dynamics, the stability analysis and the finite-time convergence analysis are more challenging than those under the well-studied consensus algorithms for known linear systems. For this purpose, we propose a novel comparison based tool. By using this tool, it is shown that the proposed nonlinear consensus algorithm can guarantee finite-time convergence if the directed switching interaction graph has a directed spanning tree at each time interval. Specifically, the finite-time convergence is shown by comparing the closed-loop system under the proposed consensus algorithm with some well-designed closed-loop system whose stability properties are easier to obtain. Moreover, the stability and the finite-time convergence of the closed-loop system using the proposed consensus algorithm under a (general) directed switching interaction graph can even be guaranteed by the stability and the finite-time convergence of some well-designed nonlinear closed-loop system under some special directed switching interaction graph. This provides a stimulating example for the potential applications of the proposed comparison based tool in the stability analysis of linear/nonlinear closed-loop systems by making use of known results in linear/nonlinear systems.     

Finite-time consensus control for second-order multi-agent systems without velocity measurements

This paper investigates the finite-time consensus problem for second-order multi-agent systems with unknown velocities and disturbances. By introducing the second-order sliding mode observer, two novel distributed finite-time protocols with only relative position measurements are proposed for the both cases with known and unknown boundaries of disturbances. On the basis of Lyapunov stability theorem and homogeneous theory, it is proved that the consensus can be achieved in finite time. Simulation examples are provided to show the effectiveness of the theoretical results.     

联合连通条件下的二阶多智能体系统有限时间一致性控制

针对时变动态拓扑下无leader的二阶多智能体系统有限时间一致性控制问题,本文给出有限时间一致性协议,并对所提出的一致性协议进行理论分析.基于图论、Lyapunov稳定性理论、同次性理论和积分不等式方法,证明了当通信拓扑为联合连通时,有限时间一致性协议可保证系统在有限时间达到一致.最后给出仿真结果,验证了理论的有效性.     

Global finite-time stabilisation for a class of stochastic nonlinear systems by output feedback

In this paper, the problem of global finite-time stabilisation by output feedback is considered for a class of stochastic nonlinear systems. First, based on homogeneous systems theory and the adding a power integrator technique, a homogeneous reduced order observer and control law are constructed in a recursive manner for the nominal system. Then, the homogeneous domination approach is used to deal with the nonlinearities in drift and diffusion terms; it is shown that the proposed output-feedback control law can guarantee that the closed-loop system is global finite-time stable in probability. Finally, simulation examples are carried out to demonstrate the effectiveness of the proposed control scheme.     

Finite-time observers for multi-agent systems without velocity measurements and with input saturations

This paper is devoted to the distributed finite-time observers for multi-agent systems, where the control inputs are required to be bounded and the velocities are assumed to be not available for feedback. An effective framework through defining a class of coordinated saturation functions is introduced, under which both a first-order finite-time observer and a high-order finite-time observer are constructed. By applying the homogeneous theory for stability analysis, it is proven that all the states of the followers can converge to that of the leader in finite time under our proposed observers. With mild modifications of our control strategies, the foregoing results are then extended to the distributed finite-time containment control problem, where the states of the followers converge to the convex hull spanned by the multiple dynamic leaders. Numerical simulations are presented to demonstrate the efficiency of our methods.     

广义时变脉冲系统的时域稳定

研究了状态依赖广义时变脉冲系统的时域稳定问题.基于微分矩阵不等式 (Differential matrix inequalities, DMI) 和S-procedure理论, 给出了两类状态依赖广义时变脉冲系统时域稳定的充分条件.接下来, 根据给出的充分条件设计了状态反馈控制器, 使得闭环系统时域稳定.最后, 给出数值算例来验证结论的有效性.     

Global finite-time control for a class of switched nonlinear systems with different powers via output feedback

This paper is concerned with the problem of global finite-time control for switched nonlinear systems whose nonlinear terms satisfy homogenous growth conditions. At first, we design homogenous output feedback controllers for nominal switched nonlinear systems by adding a power integrator method. Then, we employ the homogeneous domination approach to scale homogeneous observers and controllers to render switched nonlinear systems with lower-triangular homogenous growth condition globally finite-time stable. Finally, the proposed control method can be extended to switched nonlinear systems satisfying with upper-triangular homogeneous growth condition. Two examples are provided to demonstrate the effectiveness of the proposed control scheme.     

Finite-time disturbance attenuation of nonlinear systems

This paper is devoted to the finite-time disturbance attenuation problem of affine nonlinear systems. Based on the finite time Lyapunov stability theory, some finite-time H _∞ performance criterions are derived. Then the state-feedback control law is designed and the structure of such a controller is investigated. Furthermore, it is shown that the H _∞ controller can also make the closed-loop system satisfy finite-time H _∞ performance for nonlinear homogeneous systems. An example is provided to demonstrate the effectiveness of the presented results.