面向非沿迹成像的姿态跟踪扩展观测器滑模控制

针对地面兴趣点不沿星下点轨迹的动态非沿轨迹成像问题，设计一种结合扩展状态观测器的非奇异快速终端滑模控制器。首先根据非沿轨迹成像模型的需求推导卫星姿态参考轨迹。其次，根据由误差四元数描述的跟踪误差运动模型设计了非奇异快速终端滑模控制律。考虑到干扰抑制，引入了扩展状态观测器来观测系统的总扰动，从而降低滑模控制律中的切换增益，削弱系统抖振。然后再用模糊自适应系统对切换项进行在线逼近，柔化控制信号，进一步减振。最后，对具有干扰和参数不确定的姿态控制系统进行了数值仿真，结果表明该方法收敛速度快，控制精度高。

Attitude Tracking Sliding Mode Control Using Extended State Observer for Nonparallel Ground Track Imaging

A nonsingular and fast terminal sliding mode controller based on the extended state observer is designed for the nonparallel-ground-track imaging mode, whose ground targets and ground track are not parallel. First, the specific method of attitude adjustment for nonparallel-ground-track imaging satellite is studied to get the desired attitude trajectory. According to the tracking error dynamics and kinematics described by unit quaternion error, a nonsingular and fast terminal sliding mode controller is derived. Considering the disturbance rejection, an extended state observer is introduced to estimate the general disturbance which efficiently weaken the chattering inherent in sliding mode structure by reducing the switching gain. Furthermore, an adaptive fuzzy system is applied to approximate the switching term in the control law online to soften the control signal so as to effectively suppress the chattering. Finally, numerical simulations on the attitude tracking control for spacecraft in the presence of environmental disturbance and parameters uncertainties are performed, whose results show the designed control scheme can meet the requirements of control precision for the smart imaging with fast convergence speed and high control accuracy.