Robust fault detection and isolation in constrained nonlinear systems via a second order sliding mode observer

A robust fault detection and isolation (FDI) approach for uncertain constrained nonlinear systems (CNS) is outlined. The FDI scheme is based on a second order slidingmode observer (SOSMO). First, a closed-loop system is formed by incorporatingthe constraint terms into the system\u27s dynamic equation and then the observer is designed based on the resulting closed loop system. Stability of the SOSMO resultingfrom the utilization of equivalent control concept is then proved by assumingthat the considered uncertain CNS has a single output, and then two outputs, respectively. An attractive feature of the FDI methodology is that the diagnostic observer can directly supply the estimate of the faults, hence, making the fault isolation a simple task. Finally, an example is given to show the effectiveness of the proposed SOSMO based FDI strategy