Observability is sufficient for the design of globally exponentially stable state observers for state-affine nonlinear systems

In this paper we are interested in the problem of state observation of state-affine nonlinear systems. It is well-known that observability of the system is a necessary assumption for the state reconstruction. Our main contribution is to prove that it is also sufficient to design a globally exponentially stable observer This should be contrasted with existing results that require the strictly stronger assumption of uniform complete observability of the system. To the best of the authors' knowledge this is the first time such a result is reported in the literature. (c) 2022 Elsevier Ltd. All rights reserved.