Space-based line-of-sight tracking control of GEO target using nonsingular terminal sliding mode

This paper addresses the issue of high-precision line-of-sight (LOS) tracking of geosynchronous earth orbit target in highly dynamic conditions via spacecraft attitude maneuver. First, characteristics of the LOS motion are analyzed by a simplified linear relative motion model. Second, after transforming the quaternion-based attitude model into a double integrator system, a new nonsingular terminal sliding mode controller is proposed for spacecraft attitude tracking in a nominal case without parametric uncertainties and external disturbances. Third, an adaptive new nonsingular terminal mode controller is proposed for spacecraft attitude tracking in an uncertain case, which is done via constructing a pair of adaptive laws to estimate the parametric uncertainties and external disturbances online. The robust stability and finite time convergence property of the closed-loop system are demonstrated by Lyapunov theorem. Under control of the proposed controller, zero steady state error tracking of LOS with a smooth transition phase can be achieved in scheduled time, regardless of parametric uncertainties and external disturbances online. Finally, detailed numerical simulation results are presented to illustrate the effectiveness and performance of the proposed controllers. Contrasting simulation results shows that proposed controllers can track the desired trajectories effectively and have better performance against the controllers based on linear sliding mode and the existing fast nonsingular terminal sliding mode.     

Fault tolerant small satellite attitude control using adaptive non-singular terminal sliding mode

The Attitude Control System (ACS) plays a pivotal role in the whole performance of the spacecraft on the orbit; therefore, it is vitally important to design the control system with the performance of rapid response, high control precision and insensitive to external perturbations. In the first place, this paper proposes two adaptive nonlinear control algorithms based on the sliding mode control (SMC), which are designed for small satellite attitude control system. The nonlinear dynamics describing the attitude of small satellite is considered in a circle reference orbit, and the stability of the closed-loop system in the presence of external perturbations is investigated. Then, in order to account for accidental or degradation fault in satellite actuators, the fault-tolerant control schemes are presented. Hence, two adaptive fault-tolerant control laws (continuous sliding mode control and non-singular terminal sliding mode control) are developed by adopting the nonlinear analytical model to describe the system, which can guarantee global asymptotic convergence of the attitude control error with the existence of unknown external perturbations. The nonlinear hyperplane based Terminal sliding mode is introduced into the control law design; therefore, the system convergence performance improves and the control error is convergent in “finite time”. As a result, the study on the non-singular terminal sliding mode control is the emphasis and the continuous sliding mode control is used to compare with the non-singular terminal sliding mode control. Meanwhile, an adaptive fuzzy algorithm has been proposed to suppress the chattering phenomenon. Moreover, several numerical examples are presented to demonstrate the efficacy of the proposed controllers by correcting for the external perturbations. Simulation results confirm that the suggested methodologies yield high control precision in control. In addition, actuator degradation, actuator stuck and actuator failure for a period of time are simulated to demonstrate the fault recovery capability of the fault tolerant controllers. The numerical results clearly demonstrate the good performance of the adaptive non-singular terminal control in the event of actuator fault compare with the continuous sliding mode control.     

Adaptive sliding mode fault-tolerant control for satellite attitude tracking system

In this paper, an adaptive modified sliding mode control approach is developed for attitude tracking of a nano-satellite with three magnetorquers and one reaction wheel. A sliding variable is chosen based on finite-time convergence of the nano-satellite attitude tracking error and avoiding the singularity of the control signal. The control gain of the proposed method is developed adaptively to reduce the tracking error and improve the closed-loop control performance. The sliding variable and adaptive parameter are also employed in the reaching phase of the control law to decrease the chattering phenomenon. In addition, the finite-time convergence of attitude variables in the presence of actuator faults, inertia uncertainty, and external disturbances is proved using the extended Lyapunov theorem. The simulations are conducted to evaluate the performance of the proposed method according to different evaluation criteria. Monte Carlo simulations are also used to survey the reliability of the system in the presence of the mentioned condition.     

柔性卫星大角度机动的自适应模糊变结构控制

针对柔性卫星大角度机动过程中多种模态的强耦合非线性动力学控制问题,提出了一种自适应模糊变结构姿态控制方法.首先利用拉格朗日方程建立了带柔性附件卫星的动力学模型,然后设计变结构控制器使得系统状态能在有限时间内到达滑模面,并采用自适应模糊系统逼近系统所存在的耦合非线性项.为了削弱变结构控制项所带来的抖动,避免激发柔性附件的高频模态,采用边界层方法来代替开关项,并通过模糊规则表的方法确定边界层的厚度.仿真结果表明,所提出的控制方法既实现了柔性卫星高精度姿态控制,也保证了卫星大角度机动过程中柔性附件弹性模态的有效抑制,系统对各种干扰具有一定的鲁棒性.      

高超声速飞行器抗干扰反步滑模控制

针对存在参数不确定及外部扰动下的高超声速飞行器轨迹跟踪控制问题,研究了一种基于反步法的抗干扰滑模控制设计方法.将非线性高超声速飞行器动力学模型表达为严反馈形式分步进行设计.采用滑模控制方法进行每步的控制器设计,并提出采用扩展状态观测器（ESO,Extended State Observer）方法实现对参数不确定及外部扰动产生的内外干扰进行估计,继而在控制中补偿.扩展状态观测器能保证对干扰的估计收敛到真值附近的邻域内,从而能够保证较好的补偿效果.通过0.5°附加干扰攻角和25%的气动参数偏差下的非线性高超声速飞行器动力学模型仿真结果验证了该抗干扰滑模控制方案对内外干扰的抑制效果和闭环系统良好的跟踪性能.      

基于扰动观测器的指数时变滑模再入姿态控制

针对再入飞行器姿态控制问题,设计了一种全局鲁棒的基于扰动观测器的指数时变滑模姿态控制器,使得在存在匹配模型参数不确定性和外部扰动情况下仍能够实现精确的姿态控制。首先对飞行器模型进行反馈线性化解耦,将俯仰、滚转、偏航通道分解为3个独立的二阶系统。然后以俯仰通道为例,设计指数时变滑模控制器,使得系统具有全局鲁棒性。进一步,为了减小采用饱和函数消除滑模控制抖振而带来的系统跟踪误差,引入扰动观测器,设计了一种基于扰动观测器的指数时变滑模控制系统。最后,以某飞行器为例建立六自由度仿真模型,在考虑大气密度、转动惯量偏差以及外部高频扰动的情况下,验证了加入扰动观测器后对系统性能的提高。     

火星大气进入滑模自抗扰制导方法

针对火星探测器大气进入制导阶段存在着模型参数误差等不确定性,基于直接反馈线性化理论设计了一种滑模自抗扰进入制导方法。首先利用反馈线性化方法对跟踪系统模型进行线性化处理;在此基础上设计了滑模控制律,并利用线性扩张状态观测器估计系统的未知不确定量,在控制律中进行补偿;此外还给出了大气进入段的横向制导律。仿真结果表明,与反馈线性化方法相比,该方法设计的制导律有效地降低了模型参数误差对制导精度的影响,实现了对参考轨迹的良好跟踪,提高了探测器开伞点的精度。     

EHA反馈线性化最优滑模面双模糊滑模控制

为提高电静液作动器（EHA）控制性能,提出了一种反馈线性化最优滑模面的双模糊滑模控制方法。该方法在EHA的非线性模型上,利用反馈线性化方法将其线性化,在此基础上建立线性切换函数,并采用最优控制理论对切换函数进行设计。为削弱抖振将模糊控制算法引入滑模控制中,采用一个模糊控制器,根据最优滑模函数运动特性的数值对切换控制增益进行估计;采用另一个模糊控制器,根据滑模控制原理对切换控制项进行调整。仿真结果证明了该方法的有效性。      

Stacked recurrent neural network based high precision pointing coupled control of the spacecraft and telescopes

In some space missions especially in the field of space gravitational wave detection, the telescope needs to point to a certain target through attitude movement and pointing control. In several mainstream gravitational wave detection missions, the detector usually consists of a cluster of three identical satellites, flying in a quasi-equilateral triangular formation with a big edge length, so every satellite needs two telescopes to point each other and constitute three giant Michelson-Type interferometers. Therefore, a satellite platform system with two telescopes is researched in this paper. This research helps to characterize the attitude motion of a telescope for space astronomical observation or space gravitational wave detection, provides new method on the telescope’s high-precision pointing control. For this purpose, we derive a satellite-telescope coupling attitude model, design the sliding mode controller for satellite and the stacked recurrent neural network adaptive controller for telescope. In the stacked recurrent neural network adaptive controller design, a sliding mode control technology is adopted. In addition, we propose a combinatorial optimization method for network weights in the stacked recurrent neural network training process, that is, the output layer is corrected by the adaptive law, and the correction of other layers adopt the error backpropagation method. Finally, a numerical simulation method verifies the effectiveness of the controller design.     

高超声速滑翔飞行器的分散鲁棒姿态控制

根据高超声速滑翔飞行器的任务和特点,并考虑一阶执行器动态,建立了面向控制系统设计的飞行器姿态模型.针对模型的结构,结合分散控制和滑模变结构控制的思想设计了再入飞行段的分散鲁棒姿态控制器:采用Tornambe控制方法进行了分散鲁棒滑模面的设计,使得系统能够克服耦合及非匹配不确定性的影响实现性能优良的滑模运动;采用改进的时间次优控制方法实现了二阶滑模变结构控制律的设计,通过在线估计等效控制削弱了抖振.为验证控制器的设计,在Simulink中以某概念高超声速滑翔飞行器为对象,进行了分散鲁棒姿态控制系统和制导系统的联合仿真,仿真结果表明在存在大不确定性的情况下,可以实现对制导指令的鲁棒稳定跟踪.     

高超声速飞行器全局有限时间姿态控制方法

以高超声速飞行器6自由度模型为研究对象,设计了一种基于终端滑模的全局有限时间姿态控制方法。在控制器设计中,通过动态逆实现对俯仰、偏航和滚转通道的解耦处理。在考虑模型不确定性和外部干扰的情况下,终端滑模变结构控制方法用于保证系统的鲁棒性。同时,通过改进指数趋近律,实现闭环系统在滑模面趋近阶段和沿滑模面滑动阶段均是有限时间收敛的。基于李雅普诺夫稳定性理论,控制器的全局有限时间收敛特性得到证明。仿真实验结果验证了高超声速飞行器全局有限时间姿态控制方法的有效性。      

高超声速飞行器的干扰补偿Terminal滑模控制

研究了一种基于干扰补偿Terminal滑模的高超声速飞行器姿态控制方法.针对传统Terminal滑模控制存在的奇异问题,提出了一种简单的改进型Terminal滑模面,通过在平衡点附近从非线性滑模面切换至高增益线性滑模面,避免了控制奇异问题,同时保持了较高的收敛速度,并对改进Terminal滑模控制在干扰作用下的误差收敛特性进行了理论分析.为进一步提高控制的鲁棒性和控制精度,设计了扩张状态观测器对干扰进行估计和补偿.进行了六自由度数学仿真验证,仿真结果表明:该方法可有效提高控制系统的控制性能和鲁棒性.     

基于本征旋转的刚体姿态跟踪系统滑模控制器

对于转动惯量参数时变和参数不确定以及外部扰动和作用力矩方向偏差的刚体姿态跟踪系统,提出了采用滑模控制的方法.利用误差四元数建立数学模型,通过本征旋转进行反馈线性化得到指令角加速度.设计滑模控制律,实现指令角加速度跟踪.仿真结果表明,所求控制律对刚体姿态跟踪系统具有全局稳定性和鲁棒性.     

月球重力转弯软着陆的模糊变结构控制

针对月球软着陆的最终段,提出了以重力转弯方式进行软着陆的模糊变结构制导律.首先设计了次优滑动面,然后引入模糊控制器,使滑动变量逐渐收敛到0,实现安全着陆.考虑了发动机推力偏差、着陆器初始质量估计偏差、月球引力加速度偏差、初始条件干扰、敏感器测量误差及姿态跟踪误差.并用Monte Carlo技术验证了所设计的模糊变结构制导律具有很强的鲁棒性,能够克服各种随机偏差及干扰的影响.因此,所设计的软着陆制导律是可行的,并且只须以斜向距离和斜向速度作为输入,工程实现简单.      

时间与燃料约束的参数自主寻优变轨滑模控制

航天器相对运动轨控采用滑模控制具有较好的抗扰能力,但参数设置复杂。为贴近工程实际,引入燃料最优约束和寻优算法,提出一种综合考虑时间、燃耗以及误差的参数自主寻优滑模控制。首先,基于线性相对运动方程与指数趋近的滑模控制,建立相对运动滑模控制器模型,并由能量最优的轨迹规划器给出收敛约束时间,实现高效机动;然后,分析滑模控制器中可调参数与时间、误差的约束条件,制定了参数量级寻优规则;最后,通过惯性权值改进的粒子群算法,将误差允许范围内的最少燃料消耗作为寻优评价标准,输出最优量级与系数组合的控制参数,实现滑模的最优控制。仿真表明,使用粒子寻优器得到的参数组合,可使滑模偏差控制器在规定时间内通过最小燃料消耗令位置与速度误差稳定收敛,增加航天器在轨寿命。     

Energy-optimal reconfiguration of satellite formation flying in the presence of uncertainties

In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances.     

空空导弹敏捷转弯反作用喷气控制研究

为了提高近距空空导弹离轴发射和攻击载机后半球目标的能力,在俯仰平面内研究了使用反作用喷气控制空空导弹敏捷转弯的问题.为了实现导弹的敏捷转弯,提出了通过控制导弹姿态来控制导弹速度方向的方法,从理论上证明了该方法的可行性.考虑到反作用喷气输入的开关特性,使用滑动模态方法设计了导弹的姿态控制系统,滑动模态可达的一个充分条件为反作用喷气提供的可控力矩不小于导弹的最大气动俯仰力矩.反馈增益可以通过非线性仿真或者优化来选择.非线性仿真的结果再次表明本文提出的转弯方法的可行性,同时也表明了滑动模态姿态控制方法的有效性.      

面向重心变化的自适应飞行控制系统设计

重心的变化直接影响飞机本身的控制特性,使得控制系统设计更为复杂.针对已有方法模型依赖性强、鲁棒性差的局限性,提出了一种面向重心变化的非线性自适应飞行控制系统设计方法.该方法基于逆动力学理论和重心在线估计系统设计标称控制律,在此基础上引入自适应滑模控制单元来构建自适应补偿控制律,其中滑模控制用于保证控制的鲁棒性和稳定性,而自适应单元则通过对模型不确定性和重心估计误差的估计及补偿提高控制的适应性和控制性能.结合Lyapunov稳定性理论证明了闭环系统的稳定性.仿真结果表明:该方法能有效地实现对系统未知不确定因素的补偿,具有较强的鲁棒性.     

卫星光轴复合指向控制方法研究

卫星平台搭载光学载荷对空间运动目标进行跟踪指向技术已经成为卫星发展的重点,为了提升卫星光轴的指向范围、跟踪精度和机动性,仅依靠卫星的姿态调整已无法提升卫星光轴的性能。通过对由卫星姿态、星载光电转台和快反镜组成的卫星复合光轴指向系统的分析,需三者协同工作,输出有效叠加,才能有效提升卫星光轴的指向范围、跟踪精度和机动性。对卫星姿态控制系统、星载光电转台控制系统、快反镜控制系统进行研究建模后,确定了三者的作动频带。通过建立辅助PQ单位反馈系统,运用频率响应法设计复合指向控制器,模拟某轨道的卫星与跟踪目标的相对运动轨迹作为仿真模型的输入。仿真数据表明卫星光轴的跟踪指向误差由0.6°下降到了0.05°,证明了复合指向控制律有效提升了卫星光轴的性能。