For autonomous landing of a small quadrotor, an attitude estimation method is proposed using optical flow, and a robust controller based on signal compensation is designed. Firstly, the ratio of velocity to depth is acquired by singular value decomposition (SVD) from the general optical flow motion model, and the altitude data are obtained by integrating the ratio of vertical speed and altitude. Then, the nonlinear model of the altitude channel is divided into a nominal linear model and an equivalent disturbance considering the influences of the ground effect and other uncertainties. And a robust controller based on signal compensation is designed, which consists of a nominal controller and a robust compensator. The nominal controller is designed for the nominal system to get the desired tracking performance, and the robust compensator is applied to restrain the influence of the equivalent disturbance. Finally, it is proved that the tracking error for the altitude channel can converge to a given neighborhood of the origin in finite time by the robust controller. Landing experimental results for a small quadrotor demonstrate the effectiveness of the proposed altitude estimation method based on optical flow and the robust controller.%针对小型四旋翼无人机自主着陆问题，提出了一种基于光流的高度估计方法和基于信号补偿的高度鲁棒控制器设计方法。首先从通用光流运动模型出发，采用奇异值分解方法求解无人机线速度和深度的比值，通过对垂直速度和高度比值积分获得高度数据。其次，将考虑地效影响和其它不确定性的高度通道非线性模型分解为标称线性模型和等效扰动两部分，并设计基于信号补偿的高度鲁棒控制器，该控制器由标称控制器和鲁棒补偿器组成，其中标称控制器使得标称闭环系统达到期望的高度跟踪特性，鲁棒补偿器用于抑制等效扰动的影响。最后从理论上证明了该控制器可以保证高度跟踪误差在有限时间内收敛至指定的原点邻域内。四旋翼无人机自主着陆的实验结果验证了所提出的基于光流的高度估计和鲁棒控制方法的有效性。
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