Observer for multivariable systems of arbitrary relative order

The article considers the observer design problem for square MIMO systems in the presence of a bounded perturbation. The system is assumed to have relative order according to Isidori (so that the product of the output and input matrices is not necessarily of full rank). An observer synthesis algorithm is proposed using hierarchical feedback by the observation error. With sufficiently large feedback coefficients, any prespecified observation accuracy can be achieved.