Asymptotic Rejection of Periodic Disturbances with Uncertain Period

This paper considers the asymptotic rejection of periodic disturbances with uncertin period. It is assumed that the system dynamics are known and the disturbance is not measurable but is periodic with an uncertain or slowly varying period. A recursive scheme for identfying the period of a periodic signal is given. Two indirect adaptive digital repetitve control algorithms based on the identified period are given, one with fixed sampling time and variable period and the other with fixed period and variable sampling time. Simulation results show that the latter has better disturbance rejection performance because of the closer match of the repetitive controller period to the actual disturbance period.