Iterative Learning Control for a Flexible Wing System Under Iteration-Varying Disturbances and References

In this article, robust iterative learning controls are proposed for a flexible wing with iteration-varying disturbances and references having unknown coefficients. The unknown basis functions of the disturbances and references are supposed to be from an exosystem with unknown initial values. Then, a higher internal model is used to describe the unknown iteration-varying property. A strongly coupled reference model, inspired by the fourth-order ODEs of the Timoshenko beam equation, is firstly proven to admit bounded solutions. In this case, feedforward controls are designed for the flexible wing system, where the iteration-varying input disturbances are divided into unknown constants and known iteration-varying states. By finding two adaption laws, robust iterative learning controls are designed to guarantee the convergence of the tracking errors along the iteration axis, as well as the boundedness of the closed-loop system. Simulation examples are further provided for the robust output regulation of the wing.