Robust nonlinear control design with input and measurement disturbances

We consider strict-feedback systems with multiplicative and additive bounded disturbances in both the state measurements and the control, and show that if the sign of the multiplicative disturbances is known, then it is possible to guarantee global uniform boundedness of the states, as well as regulation of the output to a neighborhood of the desired setpoint. Our design does not require knowledge of the disturbance bounds, and its gains can be as low as desired. Of course, since the disturbance bounds are unknown, the closed-loop states converge to an unknown compact residual set. Moreover, as the controller gains decrease, the size of this residual set increases, and thus asymptotic performance deteriorates