Saturation technique for constructing observer of multi-output nonlinear systems

We present an explicit form of nonlinear observer for a class of multi-input multi-output systems. Observer construction for multi-output nonlinear systems is not a trivial extension of single-output case, especially when the global error convergence is of interest. In this paper, we confine the class such that the subsystem for each output has a triangular dependence on the states of that subsystem itself, and the overall system has a block triangular form for each subsystem. Hence, the contribution is to expand the existing results in the literature since interconnections between the subsystems are allowed. The construction is based on the saturation of some estimates, which is originated by Khalil and Esfandiari (1993) for the use of semi-global output feedback control.