Koopman operator based observer synthesis for control-affine nonlinear systems

We propose a new observer form based on Koopman operator theoretic framework for input-output nonlinear systems with control affine inputs. Based on this observer form, we describe an observer synthesis framework which exploits estimation techniques developed for Lipschitz systems and bilinear systems. We also formulate nonlinear observability rank condition in terms of the Koopman observer form, and numerically illustrate the benefits of the proposed framework.