Robustness of discrete nonlinear systems with open-closed-loop iterative learning control

In this paper, iterative learning control problem is investigated for a class of time-varying discrete nonlinear systems in the presence of different disturbances. Conditions for guaranteeing the robustness of an open-closed-loop iterative learning control system are presented. It is shown that the tracking errors of the control system are uniformly bounded in the presence of bounded state uncertainty, output disturbance and initial state error. The system can track the desired trajectory completely if all the uncertainties are gradually repeated. The conditions show that most coefficients of the iterative learning controller have no effects on the system robustness.