On non-linear unknown input observers-applied to lateral vehicle velocity estimation on banked roads

Unknown input observers (UIOs) are observers that have stable error dynamics that are independent of unknown inputs. This paper studies such observers for nonlinear systems, and shows that the error dynamics for a nonlinear UIO has the same structure as the error dynamics of a nonlinear observer without unknown inputs. This result is first used to provide synthesis inequalities for UIOs for a class of nonlinear systems, and secondly, to inspire the design of an observer for estimation of vehicle lateral velocity on banked roads.