Discrete repetitive controller with a non-integer number of samples per cycle

Repetitive controllers are used to track periodic references or to reject periodic disturbances exactly. This letter presents a simple addition for a discrete repetitive controller to tackle applications in which the period of the reference signal or disturbance is not an exact multiple of the sampling period. It can be applied when the period to be tracked is not known exactly when the sampling period is chosen but can be estimated on-line to adjust the repetitive controller.