A Block Triangular Form for Nonlinear Observer Design

This note reconsiders existence conditions for an established block triangular form (BTF) for a broad class of multi-output nonlinear systems. Systems transformable into BTF coordinates allow for decentralized observer design performed subsystem-at-a-time effectively treating upper subsystem states as measurements. Sufficient conditions are given to ensure that the output is linear in BTF coordinates. An example illustrates the BTF construction and a typical observer design