ROBUST AND NONROBUST TRACKING

For zero steady state tracking error it is necessary to include n inte grators in the control loop in the case of reference signal generated by n integrators. This result can be generalized to arbitrary n unstab le modes of the reference generator according to the ''internal model principle'' This paper shows an alternative solution of the asymptotic reference signal tracking problem using feedforward. The solution is not robust but gives a feedback controller with reduced complexity. Ro bust tracking structure with error driven controller and nonrobust con trol structure with feedforward are also compared with respect to quad ratic criteria. The alternative solution with feedforward is not asymp totically robust but sometimes gives better performance with respect t o quadratic criteria.