中文说明：
通过非线性扩张观测器可实现被控对象的位置、速度和未知部分观测。在实际控制工程中，可采用本观测器实现无需速度测量的控制，并实现对未知不确定性和外加干扰补偿。
English Description：
The position, velocity and unknown part of the plant can be observed by nonlinear extended observer. In practical control engineering, the observer can be used to realize the control without speed measurement, and realize the compensation of unknown uncertainty and external disturbance.