Robust nonlinear output feedback control for systems with unknown integrator gains

This paper shows that an output feedback stabilization problem for nonlinear systems with unknown constant integrator gains or virtual control coefficients can be reformulated in a simple procedure. As a consequence, existing robust adaptive backstepping techniques can be applied, hence all the closed loop states are globally bounded and the output can be made arbitrarily small. The procedure presented involves the scaling of unmeasured states and designing a reduced order observer.