Nonlinear Observers

This paper is a review of the existing methods for designing an observer for a system modeled by 18 nonlinear equations. We focus our attention on autonomous, finite dimensional systems described 19 by ordinary differential equations. The current condition of such a system is described by its state 20 variables about which we just have partial and possibly noisy measurements. The goal of the 21 observer is to process these measurements and any information regarding the initial state of the 22 system and to obtain an estimate of the current state of the system. This estimate should improve 23 with additional measurements and, ideally, converge to the true value in the absence of noise. The 24 observer does this by taking advantage of our a priori knowledge of the dynamics of the system. 25