Robust Tracking and Disturbance Rejection for Uncertain/Nonlinear Systems with PI Controllers

PI controllers are designed to track constant reference outputs while rejecting constant disturbances. We consider this controller structure for tracking problems where disturbance and reference signals have bounded derivatives. It is shown that tracking can be achieved with a bound on the tracking error which is determined by the bound on the derivatives of disturbance and reference signals. It is also shown that the state and control input are bounded if the disturbance and reference signals are bounded.