A necessary condition and a backstepping observer for nonlinear fault detection

A formulation of the fundamental problem of residual generation for fault detection in nonlinear systems based on the concept of output invariance is given. Consequences are derived in the geometric context. A necessary condition, which recovers the same result in the case of linear systems, and a normal form suitable for the solution of the problem are obtained. The recently introduced backstepping observer is then used as a residual generator