Bounded attitude control of rigid bodies: Real-time experimentation to a quadrotor mini-helicopter

A quaternion-based feedback is developed for the attitude stabilization of rigid bodies. The control design takes into account a priori input bounds and is based on nested saturation approach. It results in a very simple controller suitable for an embedded use with low computational resources available. The proposed method is generic not restricted to symmetric rigid bodies and does not require the knowledge of the inertia matrix of the body. The control law can be tuned to force closed-loop trajectories to enter in some a priori fixed neighborhood of the origin in a finite time and remain thereafter. The global stability is guaranteed in the case where angular velocity sensors have limited measurement range. The control law is experimentally applied to the attitude stabilization of a quadrotor mini-helicopter.     

Disturbance observer-based quadrotor attitude tracking control for aggressive maneuvers

In this paper, a disturbance observer-based quadrotor attitude controller for aggressive maneuvering is presented. The controller is made up of the cascade connection between two control-loops: an outer quaternion-based attitude control-loop and an inner disturbance observer-based angular velocity tracking control-loop. The disturbance observer is designed to estimate and compensate for the Coriolis term and the external disturbances. It is shown that, for fast maneuvers, the disturbance observer needs to take into account the motor dynamics. This allows to notably increase the observer bandwidth, leading to significant improvements in the disturbance rejection capabilities. The stability of the resulting closed-loop is analyzed. Also, different simulations and flight tests are carried out to validate the main results, showing an outstanding tracking performance when aggressive attitude maneuvers are being executed, even in the presence of strong disturbances such as suspended payloads.     

输入饱和与姿态受限的四旋翼无人机反步姿态控制

本文针对四旋翼无人机研究了鲁棒反步姿态控制策略.由于四旋翼无人机结构复杂,其非线性数学模型难以精确建立,因此在控制器设计过程中需要综合考虑模型不确定性、未知外部干扰、输入饱和以及姿态受限等因素.针对模型中的不确定项,使用神经网络进行逼近;对于外部未知干扰,使用非线性干扰观测器进行补偿;使用双曲正切函数逼近饱和函数,解决输入饱和问题;同时使用界限Lyapunov函数设计控制器,确保姿态满足限制条件.最后,设计四旋翼无人机反步姿态控制器,并根据Lyapunov稳定性定理证明了闭环控制系统的有界稳定.仿真结果表明了所研究控制方法的有效性.     

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.     

A high-performance flight control approach for quadrotors using a modified active disturbance rejection technique

In practice, the parameters of the flight controller of the quadrotors are commonly tuned experimentally with respect to a certain type of reference, such as the step reference and the unit-ramp reference. In this way, the performance of the flight controller might be affected by the variations of the references in real-time flights. Besides, real-time dynamic effects such as measure noises, external disturbances and input delays, which are usually neglected in the reported works, could easily deteriorate the performances of the flight controllers. This work is thereby motivated to develop a high-performance flight control approach utilizing a modified disturbance rejection technique for the quadrotors suffering from input delays and external disturbances. This control approach is developed in a cascaded structure and the attitude angles are chosen as the pseudo control inputs of the translational flight of the quadrotors. To facilitate the development, the dynamic model of the quadrotors is firstly formulated by including the effects of input delays, and the dynamics of the pseudo control variables are identified through real-time experiments. Based on the identified model, the flight control approach is proposed with a modified active disturbance rejection technique, which consists of a time optimal tracking differentiator, an extended state observer/predictor, and a nonlinear proportional–derivative controller. The tracking differentiator is designed to generate smooth transient profiles for the references, and the extended state observer/predictor is implemented for lumped disturbance estimation and state estimation considering the input delays. With the aid of the tracking differentiator and the extended state observer/predictor, the nonlinear proportional–derivative controller can thereby establish a fast tracking control and effectively reject the estimated disturbances. To verify the feasibilities of this development, comparative tests are carried out in both simulations and experiments. The results show that in the presence of small lumped disturbances, such as the measurement zero-drift, the steady-state errors of the proposed control approach for the ramp responses are less than 2 cm, and in the tests of sinusoidal trajectory tracking, the cross-tracking errors are less than 0.04 m. When with large disturbance airflow that is equivalent to strong breeze, the steady-state error achieved by the proposed flight controller is also less than 10 cm. All of these facts demonstrate the effectiveness of this development.     

An integrated approach to hypersonic entry attitude control

This paper presents an integrated approach based on dynamic inversion(DI)and active disturbance rejection control(ADRC)to the entry attitude control of a generic hypersonic vehicle(GHV).DI is frstly used to cancel the nonlinearities of the GHV entry model to construct a basic attitude controller.To enhance the control performance and system robustness to inevitable disturbances,ADRC techniques,including the arranged transient process(ATP),nonlinear feedback(NF),and most importantly the extended state observer(ESO),are integrated with the basic DI controller.As one primary task,the stability and estimation error of the second-order nonlinear ESO are analyzed from a brand new perspective:the nonlinear ESO is treated as a specifc form of forced Li′enard system.Abundant qualitative properties of the Li′enard system are utilized to yield comprehensive theorems on nonlinear ESO solution behaviors,such as the boundedness,convergence,and existence of periodic solutions.Phase portraits of ESO estimation error dynamics are given to validate our analysis.At last,three groups of simulations,including comparative simulations with modeling errors,Monte Carlo runs with parametric uncertainties,and a six degrees-of-freedom reference entry trajectory tracking are executed,which demonstrate the superiority of the proposed integrated controller over the basic DI controller.     

基于Kinect的四旋翼无人机体感控制

针对无人机（ UAV）远程控制中操作复杂、专业性高的问题,基于Kinect传感器提出了一种无人机体感控制方案,并进行了验证。利用Kinect传感器提取操作者身体的骨骼节点数据,设计并识别操作者体势动作,进而生成对应的四旋翼飞行控制指令,通过无线数传模块传输控制指令,对无人机进行远程控制。实验结果表明：设计的识别算法可以准确地识别体势动作,对无人机进行实时的控制,控制方式直观简单、效果良好。     

四旋翼无人机姿态系统复合连续快速非奇异终端滑模控制EI北大核心CSCD

本文针对受多源干扰影响的四旋翼无人机姿态系统,基于复合连续快速非奇异终端滑模算法,研究了姿态指令变化率未知情况下的连续有限时间姿态跟踪控制问题.首先,基于四旋翼无人机姿态回路动力学模型,通过引入虚拟控制量实现姿态跟踪误差动态的三通道解耦;其次,分别针对各通道跟踪误差动态设计高阶滑模观测器,实现跟踪误差变化率和集总干扰的有限时间估计;最后,结合姿态跟踪误差变化率的估计信息,构建动态快速非奇异终端滑模面,并在控制设计中用指数幂函数代替符号函数以保证控制量连续.并且基于Lyapunov分析方法给出了姿态跟踪误差有限时间收敛的严格证明,仿真结果验证了所提方法的有效性.     

四旋翼无人机抗干扰轨迹跟踪控制

针对四旋翼无人机轨迹跟踪过程中存在的参数不确定与外界干扰问题,设计一种双闭环自适应控制策略.为了降低控制器设计复杂度,根据四旋翼无人机系统的欠驱动特性将系统分成姿态内环和位置外环.在扰动观测器的基础上,利用积分型反步控制算法完成无人机位置信息在外界干扰下的稳定跟踪控制.在扰动观测器的基础上,利用自适应滑模控制算法完成无...     

An enhanced anti-disturbance attitude control law for flexible spacecrafts subject to multiple disturbances

As well-known disturbance rejection methods, active disturbance rejection control and disturbance observer-based control can effectively improve the control performances of complex systems in the presence of disturbances. However, the accurate rejection of multiple disturbances for control systems of practical engineering, for example, the attitude control system of flexible spacecraft, is still a bottleneck problem. In order to further improve the anti-disturbance capability and reduce the conservativeness, this paper proposes a novel enhanced anti-disturbance control law for the attitude control system of flexible spacecraft by combining active disturbance rejection control and disturbance observer-based control in a unified framework. More specifically, the disturbance from flexible vibration is described by an uncertain exogenous system based on the partially known information including elastic damping ratios and modal frequencies. The disturbance observer-based control is utilized to estimate and thereby reject this disturbance. On the other hand, the other disturbances such as external environmental disturbance and complex model nonlinearity are merged into a equivalent disturbance with bounded derivative, which is compensated by using the active disturbance rejection control law. Stability and robustness analysis are carried out for the disturbance observer and extended state observer. Finally, simulation results of low-earth-orbit flexible satellite are presented to verify the effectiveness of proposed methods.     

基于贝叶斯改进神经网络的电力无人机鲁棒姿态控制方法

针对电力无人机在工作状态下受到外部因素干扰、无法精准控制运动姿态的问题,提出基于贝叶斯改进神经网络的电力无人机鲁棒姿态控制方法。综合考虑电力无人机的组成结构、运动以及动力原理,构建电力无人机数学模型。利用传感器设备检测电力无人机的实时位姿,采用飞行路线规划的方式确定姿态控制目标。在考虑风场威胁条件和故障状态的情况下,利用贝叶斯改进神经网络计算无人机的姿态控制量,以鲁棒姿态控制器作为硬件支持,实现鲁棒姿态控制。通过性能测试得出结论:优化设计方法的姿态角控制误差始终低于0.2°,且在三种不同风场工况下,控制误差的波动程度不高于0.5°,与传统方法相比,优化设计方法在姿态控制精度和鲁棒性方面具有明显优势。     

基于反步滑模算法的无人机姿态鲁棒控制系统设计

针对传统无人机姿态鲁棒控制系统易受到外部干扰影响,无法精准控制姿态角、左侧舵面角和右侧舵面角,导致系统不稳定的问题,设计了基于反步滑模算法的无人机姿态鲁棒控制系统;使用TMS320F28335芯片的串级PID控制器,控制无人机中央处理机;选择MS-S3型伺服驱动器保证电机高速运动时的高转矩运行;使用STM32f407VGT6型号姿态控制器,控制旋翼姿态;在软件流程设计过程中,构建无人机动力学模型,引入反步滑模算法构建考虑姿态角动态方程,选择Lyapunov函数计算误差变量,设计滑模控制律,借助Visual C++6.0实现软件程序编写,完成无人机姿态鲁棒控制系统设计;由实验结果可知,在时间为5 s时,该系统姿态角达到6°、左侧舵面达到0.40°、右侧舵面角达到0.20°,与实际控制结果一致,具有精准控制效果。     

A design modification for a quadrotor UAV: modeling,control and implementation

Conventional quadrotor unmanned aerial vehicles have crucial underactuation limitations. This appears in the coupling between the roll angle and movement along the y-direction, and between the pitch angle and movement along the x-direction. The quadrotor capability of hovering with either roll or pitch angle is restricted due to these limitations. In this paper, a design modification, with experimental verification, is proposed in order to increase the quadrotor degrees of freedom and improve its hovering capability. Four additional rotations for the propellers about the axes perpendicular to the arms grant overactuated system. It could be used to make a horizontal movement with zero inclination angle which is followed in this work as an example for the skills acquired by the quadrotor due to the proposed design. Choosing different tilting axes, rather than the mostly considered ones in previous work which are about the ones along the arms, enhances the advantages of this modification. The benefits are to increase the degrees of freedom and improve the hovering of the quadrotor as well. A PID controller is utilized for practical implementation of the proposed design. Simulation and experimental results show the validity of the proposed design.     

Precision flight control for a multi-vehicle quadrotor helicopter testbed

Quadrotor helicopters continue to grow in popularity for unmanned aerial vehicle applications. However, accurate dynamic models for deriving controllers for moderate to high speeds have been lacking. This work presents theoretical models of quadrotor aerodynamics with non-zero free-stream velocities based on helicopter momentum and blade element theory, validated with static tests and flight data. Controllers are derived using these models and implemented on the Stanford Testbed of Autonomous Rotorcraft for Multi-Agent Control (STARMAC), demonstrating significant improvements over existing methods. The design of the STARMAC platform is described, and flight results are presented demonstrating improved accuracy over commercially available quadrotors.     

四旋翼无人飞行器混合控制系统研究

针对四旋翼无人飞行器质量未知情况下的垂直起降控制问题,提出一种基于状态反馈和神经网络自适应的混合控制方法。该方法通过一个状态反馈控制器实现飞行器的水平位置和航向控制,考虑到飞行器负载的未知特性,通过径向基函数(RBF)神经网络对飞行器质量进行估计,从而实现对高度的精确控制。仿真分析及验证表明,所提出的控制方法能够有效实现飞行器高度的精确控制,并能够在线估计出飞行器质量参数。     

PID control of quadrotor UAVs: A survey

The proportional–integral–derivative (PID) control is the most common control approach used in industrial and commercial mechatronics products. The PID control has been relevant across history since it is useful and intuitive in practical implementations. The selection of three parameters involving the present, past, and future of the system makes it simple and efficient. Unmanned aerial vehicles (UAVs) such as quadrotors have become very common and helpful in many tasks such as surveillance, mapping, and inspection, among others. Quadrotors present highly nonlinear and coupled dynamics that can be stabilized using four control inputs. These facts have prompted the attention of many control practitioners and theoretical specialists. The literature reveals that PID control has been the natural choice to stabilize quadrotor UAVs since its simplicity and robustness. The advantages of the PID control have been considered to perform combinations with other techniques. This paper surveys applications of PID control structures in quadrotor UAVs paying attention to linear, nonlinear, discontinuous, fractional order, intelligent and adaptive schemes. Future directions of PID control are also discussed, and open problems are highlighted.     

Spatial observer-based repetitive controller: An active disturbance rejection approach

Linear Repetitive Control has proven to be an effective strategy to compensate for periodic disturbances in mechatronic systems that operate at constant speed; however, it renders very poor performance in varying speed applications. In this work, a Repetitive Controller based on a Generalized Proportional Integral (GPI) observer under Active Disturbance Rejection approach is presented and formulated in spatial domain. The inclusion of the linear GPI observer makes possible to see the spatial non-linear system as a simplified linear one by means of an on-line estimated unified disturbance term. Experimental results show that the presented linear approach successfully rejects periodic disturbances under varying speed conditions.     

Drag-free and attitude control for the GOCE satellite

The paper concerns Drag-Free and Attitude Control of the European satellite Gravity field and steady-state Ocean Circulation Explorer (GOCE) during the science phase. Design has followed Embedded Model Control, where a spacecraft/environment discrete-time model becomes the real-time control core and is interfaced to actuators and sensors via tuneable feedback laws. Drag-free control implies cancelling non-gravitational forces and all torques, leaving the satellite to free fall subject only to gravity. In addition, for reasons of science, the spacecraft must be carefully aligned to the local orbital frame, retrieved from range and rate of a Global Positioning System receiver. Accurate drag-free and attitude control requires proportional and low-noise thrusting, which in turn raises the problem of propellant saving. Six-axis drag-free control is driven by accurate acceleration measurements provided by the mission payload. Their angular components must be combined with the star-tracker attitude so as to compensate accelerometer drift. Simulated results are presented and discussed.     

四旋翼飞行器的自抗扰飞行控制方法

针对四旋翼飞行器参数不确定性和外部干扰敏感的问题,本文提出一种基于自抗扰控制器的控制系统设计方法.在为期望姿态和高度安排过渡过程的基础上,设计了扩张状态观测器对内扰和外扰进行估计并实时补偿,能够很好地克服飞行器的强耦合性、模型不确定性以及风速变化等外部干扰问题.此外本文还设计了非线性状态误差反馈控制律来有效抑制跟踪误差.在仿真平台上对自抗扰控制系统进行稳定控制、姿态跟踪、高度控制、抗扰性及鲁棒性实验,并与串级PID控制系统进行定量对比分析.仿真结果表明,本文所设计的自抗扰控制器不仅能够很好地估计并补偿系统所受内外部干扰,而且对四旋翼飞行器参数的不确定性具有较强的鲁棒性,能够满足飞行器姿态调节快速和高稳定度的控制要求,性能指标明显优于串级PID控制器.     

主动变形四旋翼自抗扰飞行控制方法

为了获得更好的环境适应性,研究设计了一种主动变形四旋翼飞行器.飞行器的变形主要分为两种:机臂伸缩和折叠.为抑制系统所受内外扰动影响,设计了基于自抗扰控制(ADRC)技术的飞行控制器.首先对主动变形四旋翼结构进行设计,使用牛顿欧拉法建立风扰下系统动力学模型,然后分析阵风对系统影响以及动态变形时重心位置、惯性张量等参数的变化,接着将主动变形四旋翼系统解耦成6个SISO系统的组合并设计位姿自抗扰控制器,最后分别利用扩张状态观测器和非线性状态误差反馈律对系统所受扰动进行观测和补偿.仿真结果表明,本文所设计的基于ADRC飞行控制器的主动变形四旋翼具有优秀的位姿控制能力,在飞行过程中可以良好地进行变形,能够有效地观测变形的扰动和紊流风扰,具有较强的稳定性和抗扰性,同时对系统部分动力失效故障有较强的鲁棒性.