A general purpose observer architecture with application to failure detection and isolation

Proposes a general observer structure which can be employed in various estimation and control problems. The starting point is the proportional integral (PI) observer which has been shown to be effective not only in loop transfer recovery (LTR) but also in estimating and accommodating disturbances. The connections of the PI observer to a disturbance observer (DO) and an unknown input observer (UIO) are established. We show that the PI structure can be further generalized to a PI adaptive observer and a PI observer with fading property. The PI adaptive (PIA) observer expands the applicability of integral action to systems with unknown parameters, while the PI fading (PIF) observer can also accommodate transitory disturbances of unknown origin. It is also shown that, when process and sensor noises are present, a PI Kalman filter can be used to achieve the same goal. A systematic design procedure is developed for estimating both the state and the unknown inputs of a dynamic system. The results presented are applicable directly to fault detection and isolation (FDI) of systems under sensor and/or actuator failures