On unknown input observers for bilinear systems

Under appropriate transformation, the design of full-order and reduced-order observers for bilinear systems subjected to unknown inputs is proved to be equivalent to that of unknown input observers for linear ones. This result simplifies considerably the observer design comparatively to those proposed in the literature, and existence conditions of observer can be easily deduced. This approach is extended to the fault detection of bilinear systems. Existence conditions of the unknown input residual observers are given