State and fault estimation for a class of non-infinitely observable descriptor systems using two sliding mode observers in cascade

This paper presents a state and fault estimation scheme using two sliding mode observers in cascade for a class of non-infinitely observable descriptor systems. Certain states are treated as unknown inputs (or faults) to formulate an infinitely observable reduced-order system. By implementing a sliding mode observer onto this reduced-order system, all states and certain fault components can be estimated in finite time. The switching feedback term from the observer is then processed and fed into a second sliding mode observer, from which the remaining faults are estimated in finite time. The existence conditions of the scheme are investigated and presented in terms of the original system matrices, and are found to be less stringent than previous work on state and fault estimation of non-infinitely observable descriptor systems. Finally, a simulation is performed to confirm the efficacy of the proposed scheme.