降维状态观测器是非常重要的一类观测器，它使用状态反馈构成闭环系统的物理实现成为可能。降维状态观测器的设计方法很多，这里提出主要的两种：-Reduced-order state observer is a very important class of observer, which uses state feedback closed loop system, the physical realization possible. Reduced-order state observer design method are many, here for the main two: