Iterative learning control for a flexible wing system under iteration-varying disturbances and references

In this paper, we design robust iterative learning controls for a flexible wing subjected to unknown iteration-varying disturbances and references. Firstly, those signals are defined from an iteration-varying exosystem in order to make the coefficients independent of iteration numbers. A strongly coupled reference model, inspired by the fourth-order ODEs of the Timoshenko beam equation, is proven to admit bounded solutions. Following this, we design feedforward controls that incorporate with unknown coefficients and known iteration-varying terms. Two adaption laws are developed for unknown coefficients of feedforward controls and we thus propose robust iterative learning controls. For the closed-loop system, we guarantee the convergence of the tracking errors along the iteration axis, while maintaining the boundedness of the closed-loop system. Simulation examples are further provided for the robust output regulation of the wing.