A novel observer based adaptive output feedback approach for control of uncertain systems

We consider the adaptive output feedback control of nonlinear systems. Given a smooth reference trajectory, the problem is to design a controller that forces the system measurement to track it with bounded errors. The classical approach requires building a state observer. However, finding a good observer for a highly nonlinear and uncertain plant is not an obvious task. We argue that it should be sufficient to build an observer for the output tracking error. The uniform ultimate boundedness of error signals is shown through a Lyapunov stability analysis. Simulations of a nonlinear second order system illustrate the theoretical results.