Actuator fault diagnosis for affine nonlinear systems with unknown inputs

An actuator fault diagnosis approach for affine nonlinear systems with unknown inputs is presented. The proposed approach is based on an input/output relation involving not only the inputs and the outputs but also the higher derivatives of the outputs. It employs the recently developed high-order sliding-mode robust differentiators (HOSMRDs) to estimate the higher derivatives of the outputs. Under certain conditions, the proposed actuator fault diagnosis approach can be used to detect, isolate, and estimate actuator faults. A nonlinear system with an unknown input is used as an example, and simulation results show that the proposed actuator fault diagnosis approach works well in terms of fault detection, isolation and estimation.