Actuator fault isolation and estimation for uncertain nonlinear systems

This paper considers observer based actuator fault isolation schemes for a class of uncertain nonlinear systems. To deal with a broader class of uncertain non-linearities, we propose novel diagnostic observers, which combine Thau´s observer with sliding mode observers and are primarily designed for actuator fault diagnostic purposes. The uncertain nonlinearities that can be attacked may include both Lipschitz uncertain nonlinearities and those uncertain nonlinearities that are not Lipschitz but satisfy certain matching conditions. The design of observer boils down to the solving of LMIs, which can easily be done using the Matlab LMI toolbox. Using the proposed observers, two actuator fault isolation schemes are designed. Unlike the existing techniques, using only m observers in the first approach and only one observer in the second approach, our proposed schemes can isolate any number of actuator faults occurring at the same time. In addition, both proposed schemes are capable of estimating the faults.