Brief Paper - Unknown input observer design for systems with monotone non-linearities

A non-linear unknown input observer (UIO) is designed for systems with non-linearities having lower bonds on their slopes. The observer is constructed such that the non-linearity in the observer error system satisfies a sector property. Based on this property rather than the Lipschitz property, an algorithm not limited by Lipschitz constant is proposed. Further, all the parameters in the proposed non-linear UIO can be calculated by solving a linear matrix inequality. The UIO is also extended to an adaptive one for a class of uncertain non-linear systems in which the arguments of non-linear terms are perturbed by unknown parameters. Finally, simulations of electric driving system are used to illustrate the effectiveness of the UIOs.