Tracker design using composite nonlinear feedback with application to a DC servomotor

In this paper, the theory of a nonlinear control technique, i.e., the composite nonlinear feedback control is considered for robust tracking of a class of linear systems with time varying uncertain parameters and disturbances. This controller can guarantee that the tracking error decreases asymptotically to zero in the presence of time varying uncertain parameters and disturbances. For performance improvement of dynamical system, this proposed robust tracking controller consists of linear and nonlinear feedback parts without any switching element. The linear feedback law is designed to yield a closed loop system with a small damping ratio for the existence of a quick response. On the other hand, the nonlinear feedback law is designed to increase the damping ratio as the system output approaches the output of the reference model. Finally, the simulations of applying the control law on a DC servomotor positioning system are given to illustrate the validity of the results developed in this paper.