In the spirit of estimating the system states and unknown inputs simultaneously via proportional-integral observer (PIO), faults may be viewed as unknown inputs and can be estimated.

• 利用比例积分观测器能够同时估计系统的状态和未知项的思想,可将系统中的故障看作是系统的未知输入项进行故障估计,从而得到故障随时间变化的估计结果。