挠性卫星姿态跟踪自适应L2增益控制

针对在轨挠性卫星姿态跟踪时存在参数不确定、外部干扰以及控制输入受限等问题,提出了一种自适应L2增益控制方法.首先利用神经网络来逼近系统中的未知非线性动态特性,设计自适应控制律来处理系统中的不确定参数:其次设计了一鲁棒控制器使得干扰力矩对系统性能输出具有L2增益,从而实现对干扰的抑制控制.最后通过引入附加的输入误差系统,...     

基于动态滑模控制的挠性航天器姿态控制

本文采用滑动模态控制方法对挠性航天器设计了姿态镇定控制律.首先,建立了挠性航天器的数学模型.其中,挠性航天器的运动学方程采用姿态四元数描述.然后,通过引入动态切换函数,设计挠性航天器的动态滑模姿态控制律.该控制律能对滑模姿态控制律中由符号函数项引起的抖振进行抑制.采用Lyapunov方法证明了所设计的动态滑模姿态控制律能使闭环航天器姿态系统稳定.最后,通过数值仿真例子验证了所提出方法的有效性.     

含有参数不确定性的挠性航天器姿态跟踪滑模控制

对有不确定参数的挠性航天器姿态跟踪控制, 提出了一种基于滑模控制的姿态跟踪控制律. 挠性航天器动力学采用混合坐标法进行建模; 构造挠性模态观测器对挠性模态变量进行观测. 基于Lyapunov稳定性原理得到含有挠性模态观测器的滑模控制律, 并给出了全局渐近稳定性的证明. 对各个仿真结果进行比较, 显示出本文提出的滑模控制律针对航天器惯量阵不确定性具有良好的鲁棒性, 而且具有较强的扰动抑制能力.     

转动惯量存在不确定性的挠性航天器滑模姿态控制

在转动惯量存在不确定性时,采用滑动模态控制方法对挠性航天器设计了姿态镇定控制律.由于挠性模态是不可量测的,首先设计了部分状态观测器对挠性模态进行估计.进而结合滑模控制方法,提出了基于观测器的滑模姿态控制律.采用Lyapunov方法证明了在存在转动惯量不确定性时,所设计的滑模姿态控制律能使闭环航天器姿态系统稳定.最后,通过数值仿真例子验证了所提出方法的有效性.     

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.     

基于飞轮的欠驱动航天器姿态控制器设计

在以飞轮作为姿态控制执行机构的航天器中,如果部分飞轮发生故障而使得航天器欠驱动时,姿态控制性能会急剧下降.本文对两个匕轮的刚性航天器,研究了姿态控制问题.在零动量的假设下,利用Backstepping方法,为欠驱动姿态控制系统设计了一个新型的姿态控制器.设计过程分两步进行:首先,根据姿态运动学模型,设计出可使航天器姿态全局渐近稳定的控制角速率;然后,根据姿态动力学模型,得到使航天器姿态全局渐近稳定的控制力矩.该控制器为非连续控制器,可使航天器姿态误差全局一致渐近收敛为零,并使系统具有良好的动态性能.计算机仿真表明,本文所设计出的控制器是可行的.     

挠性航天器的非线性PID和PI姿态控制器设计

针对存在模型不确性和常值干扰的挠性航天器, 提出一种不依赖于模型参数的非线性PID姿态控制器. 该控制器在小姿态偏差的情况下近似经典的线性PID控制器. 另外, 考虑到航天器上陀螺失效情况, 设计了一种仅需姿态测量信息的非线性PI控制器. 这两种控制器在局部均对常值干扰有抑制作用, 并能使无干扰作用的姿态控制系统半全局渐近稳定. 闭环系统的稳定性证明采用了奇异扰动理论, 以解决积分项的存在带来的稳定性分析问题. 文章最后用数学仿真验证了控制器的性能.     

Robust adaptive attitude control for flexible spacecraft in the presence of SGCMG friction nonlinearity

This paper investigates attitude maneuver control issues of a flexible spacecraft with pyramid‐type single gimbaled control moment gyroscopes (SGCMGs) as the actuator. The LuGre friction model is adopted to precisely describe the nonlinearity of the SGCMG gimbal friction. Aiming at restraining the adverse effects of the friction existed in SGCMG on the attitude control performance, a robust adaptive attitude controller is proposed, and projection‐based adaptive laws are presented to estimate the friction parametric uncertainties and the bound of friction nonlinearity. By treating the flexible mode coupling effect and external disturbances as lump disturbances, the inertia uncertainties and the bound of the lump disturbances are also estimated and compensated simultaneously to reduce their adverse effect on the system. With the Lyapunov technique, the states of flexible spacecraft control system are proved to be uniformly ultimately bounded. Numerical simulations demonstrate the effectiveness of the proposed scheme.     

Selecting operating points for discrete-time gain scheduling

Gain scheduling is a popular approach for nonlinear control system design. A controller is obtained by designing a set of controllers at operating points and then linearly interpolating controller values between them. However, little guidance has been provided in the literature for the selection of operating points. We use interval mathematics and a classical synthesis design approach to determine a near minimal set of design points and assess the quality of a gain scheduled controller. A sufficient condition for the assignment of the system closed loop poles is developed, and an algorithm for selecting the operating points is provided. An example is given to demonstrate the approach.     

Improved LMI conditions for gain scheduling and related control problems

The gain scheduling problem considered in this paper concerns a linear system whose state-space equations depend rationally on real, time-varying parameters, which are measured in real time. A stabilizing, parameter-dependent controller is sought, such that a given ℒ︁₂-gain bound for the closed-loop system is ensured. Sufficient linear matrix inequality (LMI) conditions are known, that guarantee the existence of such ‘gain-scheduled’ controllers. This paper improves these results in two directions. First, we show how to exploit the realness of the parameters using a ‘skew-symmetric scaling’ technique. Moreover, we show how to apply this technique in a time-varying and/or nonlinear setting. We first devise a general result pertaining to control synthesis of interconnection of dissipative operators, and apply it to the gain-scheduling problem. Owing to its generality, this result can be applied to other problems such as anti-windup control, nonlinear control and model reduction. © 1998 John Wiley & Sons, Ltd.     

Robust attitude tracking control of flexible spacecraft for achieving globally asymptotic stability

The three‐axis attitude tracking control problem in the presence of parameter uncertainties and external disturbances for a spacecraft with flexible appendages is investigated in this paper. Novel simple robust Lyapunov‐based controllers that require only the attitude and angular velocity measurement are proposed. The first controller is a discontinuous one composed of a nonlinear PD part plus a sign function, whereas the second one is continuous or even smooth by modifying the discontinuous part of the first one. For a general desired trajectory, both controllers can achieve globally asymptotic stability of the attitude and angular velocity tracking errors instead of ultimate boundedness. By using a two‐step proof technique, the partial stability of the proposed controllers for the resulting closed‐loop systems in the face of model uncertainties and unexpected disturbances is proven theoretically. To further enhance the control performance, a continuous controller is presented that utilizes the tracking errors for estimating the external disturbances. In addition, stability analysis is done. For all the developed controllers, numerical simulation results are provided to demonstrate their performance. Copyright © 2008 John Wiley & Sons, Ltd.     

Robust global stabilization of spacecraft rendezvous system via gain scheduling

The problem of robust global stabilization of a spacecraft circular orbit rendezvous system with input saturation and inputadditive uncertainties is studied in this paper. The relative models with saturation nonlinearity are established based on Clohessey-Wiltshire equation. Considering the advantages of the recently developed parametric Lyapunov equation-based low gain feedback design method and an existing high gain scheduling technique, a new robust gain scheduling controller is proposed to solve the robust global stabilization problem. To apply the proposed gain scheduling approaches, only a scalar nonlinear equation is required to be solved. Different from the controller design, simulations have been carried out directly on the nonlinear model of the spacecraft rendezvous operation instead of a linearized one. The effectiveness of the proposed approach is shown.     

Stochastic tuning of a spacecraft controller using neural networks

There have been many demonstrations of the advantages of using neural networks in control systems. Networks, such as the MLP, offer a level of adaptability and non-linearity, both of which are required in some control systems. However, for spacecraft attitude control, high levels of dependability are also required. This poses serious questions for the acceptability of neural networks. This paper describes a suggested control system which uses two MLP networks for the control of thrusters on the SOHO spacecraft. However, rather than applying the networks directly, they form part of a stochastic parameter-selection system which is used to adapt a conventional (PD) control system. It is suggested that using neural networks indirectly in this way better guarantees the dependability/reliability of the control system.     

充液柔性航天器非线性姿态动力学及再定向姿态机动

研究全充液柔性航天器大角度姿态机动中非线性姿态动力学及姿态再定向问题．采用Lagrange方法推导了液-柔耦合系统动力学方程并对系统进行了相空间动力学研究．由于能量耗散及柔性附件振动对系统产生扰动并由此引起混沌姿态运动，经历姿态转换后的航天器最终姿态定向不能预先确定．本文研究表明，通过一对互为反向的脉冲推进可以完成预期的姿态再定向机动．给出了实现姿态再定向机动的控制策略，并对控制前后的姿态本体轨迹及主角动量分量时间响应历程进行了数值仿真．     

Interpolation for gain-scheduled control with guarantees

Here, a methodology is presented which considers the interpolation of linear time-invariant (LTI) controllers designed for different operating points of a nonlinear system in order to produce a gain-scheduled controller. Guarantees of closed-loop quadratic stability and performance at intermediate interpolation points are presented in terms of a set of linear matrix inequalities (LMIs). The proposed interpolation scheme can be applied in cases where the system must remain at the operating points most of the time and the transitions from one point to another rarely occur, e.g., chemical processes, satellites.     

Attitude tracking control of a flexible spacecraft under angular velocity constraints

In this paper, a new technique is proposed for trajectory tracking of a flexible spacecraft subject to angular velocity constraints. The problem is addressed using an output to input saturation transformation (OIST) which converts the prescribed bounds into state-dependent saturations on the control input signals. It is shown that an interval observer can be used in combination with the OIST technique to ensure that the constraints remain satisfied despite unmeasured flexible modes and torque disturbances. Some realistic simulations conclude the paper and validate our approach.     

挠性系统的鲁棒控制设计

提出一种新的鲁棒设计思想：将挠性模态部分的Nyquist图线安排到右半平面。由于综合运用了频域分析、极点配置、正实性引理、线性矩阵不等式等概念和算法，使得这种鲁棒控制设计得以实现，且简单直观。通过两个算例说明了该设计方法的有效性。     

Attitude synchronization control for a group of flexible spacecraft

To solve the problem of attitude synchronization for a group of flexible spacecraft during formation maneuvers, a distributed attitude cooperative control strategy is investigated in this paper. Based on the backstepping design and the neighbor-based design rule, a distributed attitude control law is constructed step by step. Using cascaded systems’ theory and graph theory, it is shown that the attitude synchronization is achieved asymptotically and the induced vibrations by flexible appendages are simultaneously suppressed under the proposed control law.     

Simultaneous design of robust gain-scheduled static output-feedback controller and scaling matrices for linear parameter varying systems with inexact scheduling parameters

This article presents a design method of the robust gain-scheduled static output-feedback controller exploiting inexact measured scheduling parameters for multi-affine linear parameter-varying systems with structured uncertainty blocks. Performance scaling matrices are introduced in the design process to reduce conservatism. By introducing auxiliary variables and properly utilizing projection lemma, a parameter-dependent linear matrix inequality with a single line search parameter is derived to synthesize the static output-feedback controller gains and scaling matrices simultaneously. Based on vertices of the convex polytope covering the admissible region of scheduling parameters and inexact ones, the given parameter-dependent synthesis condition is further expressed as a set of linear matrix inequalities at the vertices of the polytope to guarantee the robustness against inaccurate scheduling parameters. Several examples show the effectiveness of the proposed algorithm.