马尔科夫链通信拓扑下的车辆队列最优能耗控制

针对马尔科夫链通信拓扑下的车辆队列控制问题,综合考虑车辆队列的非线性动力学模型和行驶能耗优化目标,提出一种基于分布式状态观测器的车辆队列能耗优化控制方法.由于在马尔科夫链通信拓扑下,部分车辆获取的邻居车辆信息具有动态切换特性,严重影响了车辆队列控制算法的有效性和稳定性.鉴于此,首先,设计一种用于估计领航车辆状态信息的状态观测器,有效避免通讯拓扑切换对队列控制系统造成的干扰;然后,结合车辆的非线性动力学模型与队列优化目标,构建一种基于指数折扣函数的车辆队列能耗优化框架,将车辆队列的能耗优化问题转化为Riccati方程的求解问题,进而得到车辆队列的最优能耗控制输入,在此基础上,通过构造动态通信拓扑下的李雅普诺夫函数,分析车辆队列控制系统的稳定性条件,即只要每个可能的通信拓扑均需包含一个以领航车辆为根的有向生成树,就可使得该车辆队列控制系统满足稳定性和队列稳定性;最后,通过数值仿真验证所提出控制算法的可行性和有效性.     

Synchronization Control for a Swarm of Unicycle Robots: Analysis of Different Controller Topologies

This paper proposes a nonlinear synchronization controller for a swarm of unicycle robots performing a cooperative task, i.e., following a desired trajectory per robot while maintaining a prescribed formation. The effect of communication between robots is analyzed and several network topologies are investigated, e.g., all‐to‐all, ring type, undirected, among others. The stability analysis of the closed loop system is provided using the Lyapunov method. Experiments with four unicycle robots are presented to validate the control law and communication analysis. Accumulated errors over the experiment time are presented in order to determine which topology is most efficient.     

传感器测量误差下的非线性车辆队列控制

传感器测量误差对车辆队列的有效控制与稳定性造成了较大的影响;通常情况下,大多研究成果将传感器测量误差设定为分布规律已知的随机数列(如高斯分布,泊松分布等),以便采用特定的数理方法消除误差影响;然而对于控制系统中仅满足有界条件的测量误差,仍需开展进一步的深入研究;针对此类现状,以非线性车辆队列控制为研究对象,综合考虑车载传感器的有界测量误差与车辆之间的有向通信拓扑,设计一种基于滑模的车辆队列控制方法;该方法能有效解决有界传感器测量误差下的车辆队列控制问题;此外,在控制过程中利用预设性能控制(PPC,prescribed performance control)理论,进一步约束车辆队列跟踪误差,确保车辆队列的队列稳定性;最后,通过数值仿真的方式验证本文所提出控制算法的有效性和可行性。     

Cooperative control of multiple surface vessels in the presence of ocean currents and parametric model uncertainty

This paper addresses the problem of cooperative path‐following of multiple autonomous vehicles. Stated briefly, the problem consists of steering a group of vehicles along specified paths while keeping a desired spatial formation. For a given class of autonomous surface vessels, it is shown how Lyapunov‐based techniques and graph theory can be brought together to design a decentralized control structure, where the vehicle dynamics and the constraints imposed by the topology of the inter‐vehicle communication network are explicitly taken into account. To achieve path‐following for each vehicle, a nonlinear adaptive controller is designed that yields convergence of the trajectories of the closed‐loop system to the path in the presence of constant unknown ocean currents and parametric model uncertainty. The controller derived implicitly compensates for the effect of the ocean current without the need for direct measurements of its velocity. Vehicle cooperation is achieved by adjusting the speed of each vehicle along its path according to information exchanged on the positions of a subset of the other vehicles, as determined by the communication topology adopted. Global stability and convergence of the closed‐loop system are guaranteed. Illustrative examples are presented and discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Consensus of a class of second‐order nonlinear heterogeneous multi‐agent systems with uncertainty and communication delay

In this paper, a consensus problem is studied for a group of second‐order nonlinear heterogeneous agents with non‐uniform time delay in communication links and uncertainty in agent dynamics. We design a class of novel decentralized control protocols for the consensus problem whose solvability is converted into stability analysis of an associated closed‐loop system with uncertainty and time delay. Using an explicitly constructed Lyapunov functional, the stability conditions or the solvability conditions of the consensus problem are given in terms of a set of linear matrix inequalities apart from a small number of scalar parameters that appear nonlinearly. Furthermore, the linear matrix inequalities are theoretically verified to be solvable when the communication delay is sufficiently small. The effectiveness of the proposed control protocol is illustrated by numerical examples. Copyright © 2016 John Wiley & Sons, Ltd.     

含时延的车辆队列事件触发一致性控制研究

为应对通信过程中的传输时延以及车辆间连续信息交互带来的信息冗余、资源浪费,提出一种基于事件触发机制的车辆队列一致性策略,以保证车辆队列能够稳定运行;为此,构建一个考虑车辆间的跟驰行为和通信时延的三阶异质车辆队列动力学模型,提出一种基于事件触发的一致性车辆队列控制器的设计方法;在此基础上,利用Lyapunov稳定性理论和代数图论,对车辆队列的稳定性进行分析,得出了使车辆队列稳定的事件触发条件和通信时延的上界;在MATLAB平台上进行仿真实验,验证了所提车辆队列控制方法的有效性。     

基于深度强化学习的网联车辆队列纵向控制

针对车辆队列中多目标控制优化问题,研究基于强化学习的车辆队列控制方法.控制器输入为队列各车辆状态信息以及车辆间状态误差,输出为基于车辆纵向动力学的期望加速度,实现在V2X通信下的队列单车稳定行驶和队列稳定行驶.根据队列行驶场景以及采用的间距策略、通信拓扑结构等特性,建立队列马尔科夫决策过程(Markov decision process,MDP)模型.同时根据队列多输入-多输出高维样本特性,引入优先经验回放策略,提高算法收敛效率.为贴近实际车辆队列行驶工况,仿真基于PreScan构建多自由度燃油车动力学模型,联合Matlab/ Simulink搭建仿真环境,同时引入噪声对队列控制器中动作网络和评价网络进行训练.仿真结果表明基于强化学习的车辆队列控制燃油消耗更低,且控制器实时性更高,对车辆的控制更为平滑.     

Dynamic Surface Control of Constrained Hypersonic Flight Models with Parameter Estimation and Actuator Compensation

In this paper, the robust adaptive controller is investigated for the longitudinal dynamics of a generic hypersonic flight vehicle. The proposed methodology addresses the issue of controller design and stability analysis with respect to parametric model uncertainty and input saturations for the control‐oriented model. The velocity and attitude subsystems are transformed into the linearly parameterized form. Based on the parameter projection estimation, the dynamic inverse control is proposed via the back‐stepping scheme. In order to avoid the problem of “explosion of complexity,” by introducing a first‐order filtering of the synthetic input at each step, the dynamic surface control is designed. The closed‐loop system achieves uniform ultimately bounded stability. The compensation design is employed when the input saturations occur. Simulation results show that the proposed approach achieves good tracking performance.     

Universal Practical Tracking Control of a Planar Underactuated Vehicle

In this article, a universal controller is proposed for a planar underactuated vehicle to track arbitrary trajectories including feasible/non‐feasible ones and fixed points. The controller design relies on several coordinate/input transformations, auxiliary trajectory design and the back‐stepping technique. The stability analysis shows that the position and orientation tracking errors are uniformly globally practically asymptotically convergent (UGPAC), and the velocity tracking errors are uniformly globally asymptotically convergent (UGAC) to a ball of origin. Moreover, if the tracked target is in uniform rectilinear motion or motionless, the whole closed‐loop tracking error system is uniformly globally practically asymptotically stable (UGPAS). The effectiveness of proposed control law is verified by simulation examples.     

Uniform synchronization in multi‐agent systems with switching topologies

This paper deals with uniform synchronization analysis of multi‐agent systems with switching topologies. The agents are assumed to have general, yet identical, linear dynamics. The underlying communication topology may switch arbitrarily within a finite set of admissible topologies. We establish conditions under which the network is uniformly synchronized meaning that synchronization is valid under all possible switching scenarios. The primary conditions established are in terms of a pair of Lyapunov strict inequalities. Following those conditions, small gain and passivity types of conditions are proposed under which uniform synchronization is guaranteed. The proposed results are also extended to the case of observer‐based protocols. Copyright © 2015 John Wiley & Sons, Ltd.     

自主车辆队列控制系统的稳定性分析

车辆队列控制可提升交通容量与安全性、降低燃油消耗,但车辆通信过程中时延不可避免;为此,针对含通信时延的车辆队列系统,开展内部稳定性和队列稳定性分析研究;首先,利用矩阵相似变换,将高维车辆队列闭环控制系统降维拆分为若干等价的低维子系统,极大地降低了内部稳定性分析的解析难度和运算量;在此基础上,利用直接法求解了车辆队列子系统特征方程的临界虚根,从而推导了准确的时延边界,获得了车辆队列系统内部稳定的充要条件;然后,为了保证干扰沿车辆队列向后传播时不扩散,通过频域分析车辆间误差传递函数,给出了系统的队列稳定性条件,以及时延和控制器参数的指导原则;最后,通过仿真验证了所提稳定性分析方法的有效性。     

Time‐varying output formation control for linear multi‐agent systems with switching topologies

Time‐varying output formation control problems for linear multi‐agent systems with switching topologies are studied, where two types of switching topologies are considered: (1) the topology is undirected and jointly connected, and 2) each topology is directed and has a spanning tree. An output formation protocol under switching topologies is constructed using the outputs of neighboring agents via dynamic output feedback. Two algorithms are proposed to design the dynamic protocols under both jointly connected topologies and switching directed topologies. Time‐varying output formation feasibility conditions are given to describe the compatible relationship among the desired time‐varying output formation, the dynamics of each agent, and the switching topologies. The stability of the closed‐loop multi‐agent systems under the proposed two algorithms is investigated based on the common Lyapunov functional theory and the piecewise Lyapunov functional theory, respectively. In the case where the topologies are jointly connected, time‐varying output formation can be achieved for multi‐agent systems using the designed protocol if the given time‐varying output formation satisfies the feasible constraint. For the case where the switching topologies are directed and have a spanning tree, the time‐varying output formation can be realized if the output formation feasibility constraint is satisfied and the dwell time is larger than a positive threshold. Moreover, approaches to determine the output formation references are provided to describe the macroscopic movement of the time‐varying output formation. Finally, numerical simulation results are presented to demonstrate the effectiveness of the theoretical results. Copyright © 2016 John Wiley & Sons, Ltd.     

Cooperative control of multiple surface vessels with discrete‐time periodic communications

This paper addresses the problem of cooperative path‐following of networked autonomous surface vessels with discrete‐time periodic communications. The objective is to steer a group of autonomous vehicles along given spatial paths, while holding a desired inter‐vehicle formation pattern. For a given class of marine vessels, we show how Lyapunov‐based techniques, graph theory, and results from networked control systems can be brought together to yield a decentralized control structure where the dynamics of the cooperating vessels and the constraints imposed by the topology of the inter‐vehicle communication network are explicitly taken into account. Cooperation is achieved by adjusting the speed of each vessel along its path according to information exchanged periodically on the positions of a subset of the other vessels, as determined by the communications topology adopted. The closed‐loop system that is obtained by putting together the path‐following and cooperation strategies takes an interconnected feedback form where both systems are input‐to‐state stable with respect to the outputs of each other. Using a small‐gain theorem, stability and convergence of the overall system are guaranteed for adequate choices of the controller gains. Copyright © 2011 John Wiley & Sons, Ltd.     

Multi‐layer distributed protocols for robust cooperative tracking in interconnected nonlinear multiagent systems

We develop a mixed graph and optimal control theoretic formulation to design a robust cooperative control protocol for a large‐scale multiagent system with partially known interconnected first‐, second‐, or mixed first‐ and second‐order dynamics. In each case, we transform the control protocol design task to a robust communication graph design problem, which, from a cyber‐physical perspective, is interpreted as the control layer design problem for an interconnected system with unknown agent layer dynamics. According to this viewpoint, each state variable has its own control layer communication topology separate from the other state variable's communication topology and the unknown agent layer interconnection topologies. We prove that all cooperative, decentralized, and centralized tracking protocols can be treated as a single design problem and, by deriving closed‐form solutions for the robust control layer topologies, we further provide a simpler design procedure, which is only based on the matrix manipulations. Aside from the linear implementation of the protocol and the connection of the proposed formulation to the well known rules‐of‐thumb in optimal control theory, this creates a higher potential to transfer ideas to industry. Modeling uncertainties tolerable by a given control layer topology is analyzed, and a preliminary performance‐oriented analysis and design approach for large‐scale interconnected systems is discussed. We show that exactly the same steps can be followed to design appropriate control layers for both tracking and stabilization.     

Mistuning-Based Control Design to Improve Closed-Loop Stability Margin of Vehicular Platoons

We consider a decentralized bidirectional control of a platoon of N identical vehicles moving in a straight line. The control objective is for each vehicle to maintain a constant velocity and inter-vehicular separation using only the local information from itself and its two nearest neighbors. Each vehicle is modeled as a double integrator. To aid the analysis, we use continuous approximation to derive a partial differential equation (PDE) approximation of the discrete platoon dynamics. The PDE model is used to explain the progressive loss of closed-loop stability with increasing number of vehicles, and to devise ways to combat this loss of stability. If every vehicle uses the same controller, we show that the least stable closed-loop eigenvalue approaches zero as O(1/N²) in the limit of a large number (N) of vehicles. We then show how to ameliorate this loss of stability by small amounts of "mistuning", i.e., changing the controller gains from their nominal values. We prove that with arbitrary small amounts of mistuning, the asymptotic behavior of the least stable closed loop eigenvalue can be improved to O(1/N). All the conclusions drawn from analysis of the PDE model are corroborated via numerical calculations of the state-space platoon model.     

Stability of nonlinear feedback systems in a Volterra representation

Presented in this paper is a stability condition for a class of nonlinear feedback systems where the plant dynamics can be represented by a finite series of Volterra kernels. The class of Volterra kernels are limited to p‐linear stable operators and may contain pure delays. The stability condition requires that the linear kernel is non‐zero and that the closed loop characteristic equation associated with the linearized system is stable. Next, a sufficient condition is developed to upper bound the infinity‐norm of an external disturbance signal thereby guaranteeing that the internal and output signals of the closed loop nonlinear system are contained in L_∞. These results are then demonstrated on a design example. A frequency domain controller design procedure is also developed using these results where the trade‐off between performance and stability are considered for this class of nonlinear feedback systems. Copyright © 2000 John Wiley & Sons, Ltd.     

Output feedback quantized observer‐based synchronization of linear multi‐agent systems over jointly connected topologies

The synchronization problem of linear over‐actuated multi‐agent systems with unmeasurable states is studied in this paper, under both limited communication data rate and switching topology flows. A class of adaptive quantized observer‐based encoding–decoding schemes and a class of certainty equivalence principle‐based control protocols are proposed. By developing the graph‐based space decomposition technique and analyzing the closed‐loop quantized dynamic equations, it is shown that if the network topology flow is jointly connected, the communication channels are periodic active, and the agent dynamics is observable, and with the orthogonal system matrix, the proposed communication and control protocols can ensure the closed‐loop system to achieve synchronization exponentially fast with finite bits of information exchange per step. Copyright © 2015 John Wiley & Sons, Ltd.     

Robust Adaptive Fractional‐Order Terminal Sliding Mode Control for Lower‐Limb Exoskeleton

This paper introduces a robust adaptive fractional‐order non‐singular fast terminal sliding mode control (RFO‐TSM) for a lower‐limb exoskeleton system subject to unknown external disturbances and uncertainties. The referred RFO‐TSM is developed in consideration of the advantages of fractional‐order and non‐singular fast terminal sliding mode control (FONTSM): fractional‐order is used to obtain good tracking performance, while the non‐singular fast TSM is employed to achieve fast finite‐time convergence, non‐singularity and reducing chattering phenomenon in control input. In particular, an adaptive scheme is formulated with FONTSM to deal with uncertain dynamics of exoskeleton under unknown external disturbances, which makes the system robust. Moreover, an asymptotical stability analysis of the closed‐loop system is validated by Lyapunov proposition, which guarantees the sliding condition. Lastly, the efficacy of the proposed method is verified through numerical simulations in comparison with advanced and classical methods.     

Finite‐time tracking control of a nonholonomic mobile robot

In this paper, the finite‐time tracking problem is investigated for a nonholonomic wheeled mobile robot in a fifth‐order dynamic model. We consider the whole tracking error system as a cascaded system. Two continuous global finite‐time stabilizing controllers are designed for a second‐order subsystem and a third‐order subsystem respectively. Then finite‐time stability results for cascaded systems are employed to prove that the closed‐loop system satisfies the finite‐time stability. Thus the closed‐loop system can track the reference trajectory in finite‐time when the desired velocities satisfy some conditions. In particular, we discuss the control gains selection for the third‐order finite‐time controller and give sufficient conditions by using Lyapunov and backstepping techniques. Simulation results demonstrate the effectiveness of our method. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Consensus strategy for a class of multi‐agents with discrete second‐order dynamics

This paper investigates consensus strategies for a group of agents with discrete second‐order dynamics under directed communication topology. Consensus analysis for both the fixed topology and time‐varying topology cases is systematically performed by employing a novel graph theoretic methodology as well as the classical nonnegative matrix theory. Furthermore, it is shown that the necessary and sufficient condition for the agents under fixed communication topology to reach consensus is that the communication topology has a spanning tree; and sufficient conditions for the agents to reach consensus when allowing for the dynamically changing communication topologies are also given. Finally, an illustrative example is provided to demonstrate the effectiveness of the proposed results. Copyright © 2011 John Wiley & Sons, Ltd.