Tracking and disturbance rejection in nonlinear systems: the integral manifold approach

The authors study the tracking and disturbance rejection problem of a class of time-invariant nonlinear systems which are linear equivalent to controllable linear systems. By using a nonlinear feedback control and a slowly varying integral control, the closed-loop system asymptotically tracks a reference input and rejects disturbances which are both unknown and slowly varying. The integral manifold concept is used to design a nonlinear controller