Scheme and application of dual analytic model based fault isolation and estimation

Existent problem of observer based fault detection and isolation is analyzed systemically, and a novel scheme for fault diagnosis is originated based on nominal model and unknown input observer (UIO), which is called dual analytic scheme. The scheme designs UIO from the viewpoint of observing faults instead of estimating states, and then uses the state error between nominal model and UIO to modify and substitute the state estimation error of UIO, so as to establish feasible and practical analytic expression for fault isolation and estimation. The scheme was applied to the fault diagnosis of a three-axis stabilized satellite actuators/sensors, and five simulated reaction wheel/gyro composite faults were isolated and estimated correctly, which demonstrates the efficacy of the dual analytic scheme. Also, it can be seen from the design and application of the scheme that the design of the scheme is simple and has no existence limitation, which effectively extends the application range and depth of observer based fault diagnosis.