Estimation and rejection of aperiodic disturbance in a modified repetitive-control system

This study concerns the problem of aperiodic-disturbance estimation and rejection in a modified repetitive-control system (MRCS). First, the configuration of an improved MRCS with an equivalent-input-disturbance (EID) estimator is constructed. The aperiodic disturbances are estimated by the EID estimator and their effect to the output channel are compensated by directly incorporating the estimates into the repetitive-control law. Next, the small gain theory and the separation theorem are used to derive the stability criterion. Then, the two-dimensional system approach and pole assignment are employed to constitute two independent design algorithms, one for the design of the state-feedback gains of the MRCS and one for the design of the EID estimator. Finally, a numerical example demonstrates the validity of the method.