On the design of robust servomechanisms for minimum phase nonlinear systems

We consider a single-input single-output nonlinear system which has a well- defined normal form with asymptotically stable zero dynamics. We study the design of a robust output feedback controller that incorporates a linear se rvo compensator to achieve asymptotic tracking and disturbance rejection. W e determine the least amount of precise information about the plant that is needed to design the controller. Such design will be robust to plant param eters and uncertainties which are not used in the design calculations. We a lso study robustness of the design to errors in determining the linear serv o compensator. Such errors could arise from approximating a general continu ous nonlinear function by a polynomial one, or from errors in determining t he frequencies of the exogenous signals. We give regional as well as semigl obal results. Copyright (C) 2000 John Wiley & Sons, Ltd.