Fault Estimation Method for Nonlinear Systems With Perturbations Based on Augmented Fault Observer

This paper proposes a robust fault estimation method for nonlinear systems with both actuator and sensor faults. Specifically, a singular system is constructed by combining the state vector of the system with the fault vector of the sensor, and an augmented fault observer is designed by combining the fault estimation algorithm of the adaptive actuator. First, an augmented fault observer for linear systems with perturbations is designed, and the sufficient conditions for the asymptotic stability of the observation error system are ascertained so that the state of the singular system can be observed. Second, considering the nonlinear characteristics of the actual control system, sufficient conditions for the existence of the augmented fault observer are determined. Finally, the design method of augmented fault observer for nonlinear systems is extended to nonlinear systems with both input interference and sensor disturbance, and sufficient conditions for the existence of the observer are found. In the design of the observer, the influence of disturbance on the system fault estimation, convergence speed of fault estimation error, and convenience of observer design are considered. Moreover, an estimation method is devised for the fault diagnosis of actuators and sensors in the control system. Finally, a numerical example that tests the design method of augmented fault observer and effect of system fault estimation is presented. The superiority and effectiveness of the method are thus verified.