A robust servomechanism problem for uncertain nonlinear systems

The robust servomechanism problem, also known as the robust output regulation, is considered in this paper for a class of uncertain triangular systems. In contrast to the previous work (Chen, 2004) where the bounding system of the controlled plant was required to be linear growth in the unmeasurable states and polynomial growth in the system output, we show that the polynomial growth condition can be relaxed and robust output regulation by error feedback can still be achieved, as long as the uncertain system is dominated by a C^o function of the system output multiplied by a linear growth of the unmeasurable states