Global Adaptive Output Feedback Control of Uncertain Nonlinear Systems with Linear and Quadratic Dependency of the Unmeasured States

In this paper, we present a global adaptive output feedback control scheme for a class of uncertain nonlinear systems to which adaptive observer backstepping method may not be applicable directly. The allowed output feedback structure includes quadratic dependency of the unmeasured states and output-dependent nonlinearities appearing not only additively, but also multiplicatively. Our novel design technique employs a change of coordinates and adaptive backstepping. With these proposed tools, we can remove linear and quadratic dependence on the unmeasured states in the state equation. From the transformed systems, a state observer can be constructed in a very easy way. The overall scheme achieves globally exponential convergence of the tracking error to zero while maintaining global boundedness of all the signals and states.