无人机编队飞行的分布式控制策略与控制器设计

针对一种小型无人机模型及其编队飞行的实际背景和限制条件,分析了编队飞行所必须涉及的队形保持、约束条件以及行为协调等关键性问题,进而引入分布式编队飞行控制策略并简要介绍了其优越性.根据分布式策略的层级概念,先后讨论了单机控制器的设计与上层的编队控制器的设计.最后分别进行了单机的FDC(flight dynamic and control)仿真和双机编队仿真.仿真结果表明,设计的控制器在执行效率和控制性能等方面具有突出的优势.     

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.     

Leader-follower finite-time formation control of multiple quadrotors with prescribed performance

This paper investigates the leader-follower formation problem for a group of quadrotors. Finite-time control scheme and prescribed performance control method, which are regarded as two highlights, are introduced in this paper. First, a control scheme with prescribed performance is used to control the translational movements to ensure the quadrotors obtain a relative gentle transient process and an adjustable steady-state error bound. Then, the desired orientations for the rotation subsystem provided by translational movements part are stabilised by a fixed-time control law. Finally, by designing a finite-time formation controller, followers can track the desired position and heading angle in finite time, which is important for the practical application. Several simulation results are given to show the effectiveness of the designed control 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.     

Robust attitude controller design for miniature quadrotors

This paper addresses the robust attitude control problem of miniature quadrotors. A simplified linear dynamical model is obtained for each attitude angle, whereas nonlinear dynamics, interaxis coupling, parameter perturbations, and external disturbances are considered as uncertainties. For each channel, a linear time‐invariant and decoupled robust controller are proposed based on a linear reduced‐order observer and a robust compensator. The observer is applied to estimate the angular velocities, and the robust compensator is introduced for reducing the effects of uncertainties. It is proven that the estimation errors of angular velocities and angular tracking errors can converge to the given neighborhood of the origin in a finite time. Experimental results on the miniature quadrotor are presented to verify the effectiveness of the proposed control approach. Copyright © 2015 John Wiley & Sons, Ltd.     

Distributed finite‐time formation control for multiple quadrotors via local communications

This paper investigates finite‐time formation tracking control problem for multiple quadrotors with external disturbance. The states of the virtual leader are not available to all the followers and the network topology is described by a directed graph. The model of each quadrotor is divided into position subsystem and attitude subsystem. Firstly, novel distributed finite‐time state observers are designed to estimate the relative state errors between followers and the virtual leader. Secondly, the values of these observers are used to design controllers that achieve finite‐time robust coordinated tracking in the position subsystem. Thirdly, the terminal sliding mode disturbance observers and finite‐time attitude tracking controllers are proposed, respectively, in the attitude subsystem to estimate the external disturbance and achieve attitude tracking control. The finite‐time stability analysis of the control algorithms is carried out using the Lyapunov theory and the homogeneous technique. Finally, the efficiency of the proposed algorithm is illustrated by numerical simulations.     

基于SO(3)的多四旋翼无人机编队协同控制

针对多四旋翼无人机系统的编队飞行问题,提出了基于特殊正交群SO(3)的协同控制设计方法.在给出编队空间队形和通信拓扑描述后,建立了多四旋翼无人机系统SO(3)控制模型.由于SO(3)与传统俯仰/偏航/滚转三通道模型具有不同的结构,文中进一步研究了SO(3)中无人机之间相对误差的表示方法,设计了适用于多飞行器的SO(3)控制器实现对编队和姿态的协同控制.推力控制器用于调节无人机的位置与速度,并在此基础上构造旋转矩阵形式的姿态协同指令.文中相应设计了SO(3)姿态控制器用于实现指令跟踪,最后从理论上对协同稳定性进行了分析.提出的控制方法能够使得多四旋翼无人机形成期望的队形,并且保持姿态一致进行稳定飞行.仿真结果验证了本文方法的有效性.     

Energy-based approach for flight control systems design

We consider the fundamentals of the energy-based approach to spatial motion control. The resulting energy balance equation establishes quantitative relations between all energy sources and consumers in the system of objects “flying vehicle—thrust system—external environment.” We establish the structure and further modification of an energy-based flight control system. The energy balance equation lets us estimate the level of atmospheric disturbances and formulate the commanding control index for engine thrust under winds of complex structure. For ground-based stages, we show a prediction method for the takeoff energy possibilities with air traffic obstacles; for situations of interrupted takeoff, the possibilities to stop inside the runway.     

Linear-adaptive flight control design for re-entry vehicles

This paper presents a linear-adaptive design technique intended for the very severe parameter variation problems encountered in lifting re-entry vehicles and in flight control of modern aircraft. The technique is illustrated by means of a detailed application to the pitch axis stability augmentation system of the X-15. The problem is to obtain satisfactory vehicle response to command inputs and disturbances, despite the extremely large variations in vehicle parameters, which are encountered when Mach number varies from 6.0 to 0.2 and altitude varies from 160,000 ft to ground level. The given time domain specifications are translated into approximately equivalent frequency response restrictions, enabling the design details to be executed in the frequency domain. This results in the maximum economy in the gain and bandwidth of the system loop transmission. The design is verified by finding the time responses for some of the extreme conditions. The practicality of the design is discussed in terms of the gain and bandwidth demands on the compensating networks, the higher order airframe dynamics and the effects of any overdesign on the system saturation tendencies.     

Robust flight control law design for an automatic landing flight experiment

The Automatic Landing FLight EXperiment, ALFLEX, was conducted by the National Aerospace Laboratory and National Space Development Agency of Japan, in order to develop their automatic landing technology for future unmanned reentry space vehicle. All the flight experiments were successfully completed. Because the ALFLEX vehicle is an unmanned and autonomous vehicle which has tip-fin wings, the flight control law has to achieve high-response-performance and robustness simultaneously. In this paper, the design method used to achieve these objectives is presented, as well as the results of flight experiments related to performance and robustness.