非完整约束多智能体系统基于屏障控制函数的分布式协同控制

本文设计了一种基于屏障控制函数(CBF)的分布式协同控制算法,实现了领航–跟随者框架下非完整约束多智能体系统的连通性与编队控制.首先,通过将连通性保持问题建模为系统约束,定义了该约束的调零屏障函数(ZBF).其次,在此基础上,构建李雅普诺夫函数与角速度输入之间的关系,对跟随者智能体设计了基于调零屏障函数的协同控制算法,其中线速度控制器保证跟随者的速度的跟踪与队形的跟踪,而梯度型角速度控制器实现跟随者角度的矫正.然后,利用调零屏障函数不变集相关引理证明了连通性约束集为正不变集,若初始时刻连通,则跟随者智能体始终与领航者保持连通性.同时,本文提出的算法实现编队误差的渐近收敛.本文中的队形适用常见的固定队形编队需求,也适用于领航者是动态(有线速度和角速度)的情况.最后,通过数值仿真进一步验证了该算法在不同队形需求下的有效性.     

Adaptive fractional-order nonsingular fast terminal sliding mode formation control of multiple quadrotor UAVs-based distributed estimator

This paper mainly solves two major problems that are unavoidable in leader–follower formation process of quadrotor UAV group: the existence of external uncertainty disturbance and communication limited between quadrotor unmanned aerial vehicle (UAV) group. To solve the problem that only one of the followers in the leader–follower formation can obtain the leader's information, an improved distributed estimator is proposed in this paper, which can accurately estimate the leader's information for each follower. In addition, in order to eliminate the influence of uncertain external disturbance on the performance of quadrotor UAV, an adaptive estimation law is designed based only on velocity and position variables. For the attitude and position subsystem of the quadrotor UAV, a sliding surface with fractional-order term is designed. Which makes the quadrotor UAV tracking error system obtain good robustness at the stage of reaching the sliding surface and fast convergence and accurate tracking performance in the sliding stage. Based on Lyapunov stability theory, the convergence results are analyzed strictly. The results show that the algorithm can make the position distance between leader and followers converge to the desired offset. Simulation results verify the effectiveness and superiority of the control algorithm.     

Variable Structure Feedback Construction Algorithm for controlling measurement-imploded leader–follower ground robots

This paper presents a systematic approach for decreasing the error growth of a formation system consisted of a leader and a number of followers which are open-loop in position measurements (position, linear velocity and relative distance to the leader). Using conventional algorithms to control such a system may lead to an unstable network with increasing consensus error. A 3-phase algorithm is proposed to address open-loop systems of the mentioned form. The algorithm is specifically beneficial to the case where linear velocity and position sensors get damaged. The main idea of the proposed algorithm is to use fundamental relations between feedbacks and construct some of them using the others which in case of car-like ground vehicles, angular sensors’ feedbacks are used to estimate linear feedbacks. The error and input mathematical relations are formulated using kinematic of car-like robots. The stability of the proposed method is proved using a quadratic CLF, and the numerical simulation results are presented to assess the effectiveness of the algorithm compared to a conventional open-loop form. The algorithm is also applied on a pair of ground car-like robots. The experimental results verify the conclusions based on simulation. Various simulation results show that the proposed algorithm has improved the divergence rate of follower’s path from leader’s, from 0.3 $\frac{m}{sec}$ for the unit of velocity’s uncertainty to about zero.     

Distributed attitude synchronization control for multiple flexible spacecraft without modal variable measurement

This paper solves the attitude synchronization and tracking problem for a group of flexible spacecraft without flexible‐mode variable measurement. The spacecraft formation is studied in a leader‐following synchronization scheme with a dynamic virtual leader. With the application of adaptive sliding‐mode control technique, a distributed modified Rodriguez parameters‐based dynamic controller is proposed for flexible spacecraft without requiring modal variable measurement. It is proved that the attitude synchronization and tracking can be achieved asymptotically under the control strategy through the Lyapunov's stability analysis. Furthermore, a distributed robust continuous control algorithm is designed to guarantee the ultimate boundedness of both the attitude tracking error and the modal variable observation error when bounded external disturbances exist. Some numerical simulation examples for multiple flexible spacecraft formation are given to demonstrate the effectiveness of the proposed method.     

基于二阶一致性算法的多仿生机器鱼分布式编队控制

针对动态领航者按照自身动力学模型运动, 多个跟随者机器鱼以其为编队参考点, 根据编队要求形成队形并整体跟随领航者运动的问题, 提出一种多仿生机器鱼分布式编队控制方案. 首先, 基于二阶一致性算法给出各跟随者机器鱼估计领航者位姿信息的分布式算法;其次,给出以领航者为参考点的多仿生机器鱼编队描述方法,进而各机器鱼根据编队要求以所估得的参考点信息实时确定其在编队中的期望位姿; 再次, 各跟随者机器鱼以期望速度和角速度以及所估得的领航者位姿信息为输入, 利用模糊控制器确定其速度档位和方向档位, 实现编队的形成与保持. 仿真和实验结果均表明, 所提分布式编队控制方法是有效的, 仿生机器鱼群体能够较快形成期望队形并跟随领航者游动.     

Adaptive fault‐tolerant formation control for quadrotors with actuator faults

In this paper, we investigate the fault‐tolerant formation control of a group of quadrotor aircrafts with a leader. Continuous fault‐tolerant formation control protocol is constructed by using adaptive updating mechanism and boundary layer theory to compensate actuator fault. Results show that the desired formation pattern and trajectory under actuator fault can be achieved using the proposed fault‐tolerant formation control. A simulation is conducted to illustrate the effectiveness of the method.     

仅考虑位置信息连通性保持的群体机器人集结控制

研究速度信息未知情形下的群体机器人集结控制问题.分别针对未设置虚拟领导者和设置虚拟领导者两种情形,提出了仅考虑位置信息的观测器和具有网络连通性保持的分布式控制方法.理论分析表明该算法具有网络连通性保持功能,并且保证所有机器人的速度信息收敛到一致,机器人最终也会聚集到一起.数值仿真实验验证了所提出分布式控制算法的有效性.     

基于旋转矩阵描述的航天器无角速度测量姿态跟踪无源控制

利用系统无源性和旋转矩阵性质研究无角速度测量下的姿态跟踪控制问题. 为了避免姿态参数的奇异性和模糊性, 提出基于三维特殊正交群(SO(3)) 的控制策略. 首先利用旋转矩阵建立姿态跟踪误差方程, 然后分析了系统的内在无源性, 从而揭示了闭环系统的稳定性. 当角速度无法获得时, 利用新的无源滤波提出一种无角速度测量控制律, 并给出了严格的Lyapunov 稳定性分析. 最后, 通过数值仿真验证了所提出的控制方法的有效性.

     

Robust formation control of multiagent systems on the Lie group SE(3)

This paper addresses the robust formation control problem of multiple rigid bodies whose kinematics and dynamics evolve on the Lie group SE(3). First, it is assumed that all followers have access to the state information of a virtual leader. Then, a novel adaptive super‐twisting sliding mode control with an intrinsic proportional‐integral‐derivative sliding surface is proposed for the formation control problem of multiagent system using a virtual structure (VS) approach. The advantages of this control scheme are twofold: elimination of the chattering phenomenon without affecting the control performance and no requirement of prior knowledge about the upper bound of uncertainty/disturbance due to adaptive‐tuning law. Since the VS method is suffering from the disadvantages of centralized control, in the second step, considering a network as an undirected connected graph, we assume that only a few agents have access to the state information of the leader. Afterward, using the gradient of modified error function, a distributed adaptive velocity‐free consensus‐based formation control law is proposed where reduced‐order observers are introduced to remove the requirements of velocity measurements. Furthermore, to relax the requirement that all agents have access to the states of the leader, a distributed finite‐time super‐twisting sliding mode estimator is proposed to obtain an accurate estimation of the leader's states in a finite time for each agent. In both steps, the proposed control schemes are directly developed on the Lie group SE(3) to avoid singularity and ambiguities associated with the attitude representations. Numerical simulation results illustrated the effectiveness of the proposed control schemes.     

Distributed output-feedback formation tracking control for unmanned aerial vehicles

This paper considers the output-feedback formation problem of tracking a desired trajectory for a group of networked unmanned aerial vehicles (UAVs). By introducing a state observer, the controller for the non-holonomic UAV model can be designed without linear and angular velocities measurements. The formation robustness can be improved by applying the virtual structure and synchronising the path parameters. It is proved that, with the proposed control strategy, all the closed-loop signals are bounded and the formation tracking errors asymptotically converge to zero. Simulation results are given to illustrate the effectiveness of the proposed control strategy.     

基于图论法的四旋翼三角形结构编队控制

针对四旋翼无人机编队控制,提出了一种基于图论法的四旋翼三角形结构编队.本文将四旋翼无人机编队整体视为一幅有向图,四旋翼为有向图中的点,四旋翼间的距离及通讯状态为有向图的边;结合Leader-Follower理论,通过相应的距离反馈控制律对领航者和跟随者设计不同的控制策略;进而使三架四旋翼无人机彼此间相对的距离收敛到一个稳定的值,最终形成一个固定的三角形结构编队.仿真研究和结果验证了本文提出编队控制策略的有效性和优越性.     

Robust adaptive fault estimation and fault tolerant control for quadrotor attitude systems

ABSTRACT

This paper addresses the problem of fault estimation and fault tolerant control for quadrotor unmanned aerial vehicle. Firstly, a robust adaptive fault estimation observer (AFEO) is proposed to achieve fault estimation of quadrotor with actuator fault in the presence of external disturbances and parameter uncertainties. Furthermore, based on the estimation of fault, a dynamic output feedback fault tolerant controller (DOFFTC) is designed to stabilise the closed-loop system with faults and uncertainties. Sufficient conditions for the existence of both AFEO and DOFFTC are given in terms of linear matrix inequalities. Finally, simulation results are presented to illustrate the effectiveness of the proposed strategy.     

四旋翼无人机SO(3) 滑模变结构姿态控制器设计

为了提高四旋翼无人机SO(3) 控制的动态性能, 对滑模变结构控制在四旋翼无人机SO(3) 姿态控制中的应用进行研究. 首先, 通过对两种四旋翼SO(3) 姿态控制模型进行分析, 确定一种奇异点较少的模型为控制对象; 随后,针对可能出现的控制奇异问题, 设计一种引入调节函数的无奇异积分型滑模面, 得到了滑模稳定性引理; 最后, 利用这种滑模面进行控制器设计和Lyapunov 稳定性分析, 证明了系统全局指数渐近稳定. 仿真结果验证了所提出的设计方案的正确性.

     

Velocity‐free attitude stabilization with inertial vector measurements

This paper deals with the attitude stabilization problem of a rigid body, where neither the angular velocity nor the attitude is used in the feedback; only body‐referenced vector measurements are needed. The proposed control scheme is based on an angular velocity observer‐like system relying solely on vector measurements. The proposed controller ensures almost global asymptotic stability and provides some interesting performance properties through an appropriate tuning of the control gains. The performance and effectiveness of the proposed control scheme are illustrated via simulation results where the control gains are adjusted using a nonlinear optimization. Copyright © 2015 John Wiley & Sons, Ltd.     

四旋翼飞行器增稳混合控制器

针对四旋翼飞行器在不同环境下的飞行稳定性问题,提出反步法和模糊自适应比例积分微分(PID)方法的混合控制方法。该方法根据无人机(UAV)飞行环境和大倾角、大倾角变化率选择当前合适的控制器。在系统未受扰动时,基于Backstepping的控制方法能够完成飞行器的轨迹跟踪;在受扰动时,基于模糊自适应PID能够极大地抑制扰动带来的影响,实现对四旋翼飞行器的精确控制。通过Matlab仿真分析及实际飞行器实验,验证了增稳混合控制器的稳定性。     

Flocking of multi‐agent dynamical systems with intermittent nonlinear velocity measurements

In this paper, the problem of flocking control in networks of multiple dynamical agents with intermittent nonlinear velocity measurements is studied. A new flocking algorithm is proposed to guarantee the states of the velocity variables of all the dynamical agents to converge to consensus while ensuring collision avoidance of the whole group, where each agent is assumed to obtain some nonlinear measurements of the relative velocity between itself and its neighbors only on a sequence of non‐overlapping time intervals. The results are then extended to the scenario of flocking with a nonlinearly dynamical virtual leader, where only a small fraction of agents are informed and each informed agent can obtain intermittent nonlinear measurements of the relative velocity between itself and the virtual leader. Theoretical analysis shows that the achieved flocking in systems with or without a virtual leader is robust against the time spans of the agent speed‐sensors. Finally, some numerical simulations are provided to illustrate the effectiveness of the new design. Copyright © 2011 John Wiley & Sons, Ltd.     

Robust formation tracking control of mobile robots via one-to-one time-varying communication

We solve the formation tracking control problem for mobile robots via linear control, under the assumption that each agent communicates only with one ‘leader’ robot and with one follower, hence forming a spanning-tree topology. We assume that the communication may be interrupted on intervals of time. As in the classical tracking control problem for non-holonomic systems, the swarm is driven by a fictitious robot which moves about freely and which is a leader to one robot only. Our control approach is decentralised and the control laws are linear with time-varying gains; in particular, this accounts for the case when position measurements may be lost over intervals of time. For both velocity-controlled and force-controlled systems, we establish uniform global exponential stability, hence consensus formation tracking, for the error system under a condition of persistency of excitation on the reference angular velocity of the virtual leader and on the control gains.     

基于故障程度的四旋翼无人机容错控制

针对四旋翼无人机执行机构部分失效故障,采用一组线性二次最优控制器,并且设计了可变因子二阶卡尔曼滤波器在线快速估计状态和检测故障。当故障被检测和诊断出来时,通过可变因子二阶卡尔曼滤波器调节,同时切换到相应的线性二次最优控制器使故障影响变小。最后,在Matlab实验平台上对所提方法的可行性和有效性进行仿真验证验证,结果表明四旋翼无人机执行机构在发生部分失效故障时,输出信号能够快速跟踪轨迹,实现了对执行机构部分失效故障的容错控制。     

Cooperative Control of Multiple UAVs for Moving Source Seeking

Advances in multi-agent technologies and UAV technologies make it possible to take advantage of cooperation of multiple UAVs for source seeking. This paper focuses on moving source seeking using multiple UAVs with input constraints. Firstly, a least-squares method is introduced to estimate the gradient of the scalar field at the leader UAV location based on the measurements of all UAVs. Since the moving source velocity is unknown, an adaptive estimator is designed to obtain the velocity. Based on the estimated gradient and source velocity, a guidance law and a sliding mode based heading rate controller are proposed for the leader UAV to achieve level tracking. Heading rate controller for each follower UAV is also developed to achieve circular formation around the leader UAV. Furthermore, the gradient estimation error is analyzed and its influence on moving source velocity estimation and level tracking accuracy is explored as well. Finally, simulation results are provided to verify the proposed approach.