Digital repetitive control is a technique which al- lows to track periodic references and/or reject peri- odic disturbances. Repetitive controllers are usually de- signed assuming a fixed frequency for the signals to be tracked/rejected, its main drawback being a dramatic per- formance decay when this frequency varies. A usual ap- proach to overcome the problem consists of an adap- tive change of the sampling time according to the refer- ence/disturbance period variation. However, this sam- pling period adaptation implies parametric changes af- fecting the closed-loop system behavior, that may compro- mise the system stability. This article presents a design strategy which allows to compensate for the parametric changes caused by sampling period adjustment. Stabil- ity of the digital repetitive controller working under time- varying sampling period is analyzed. Theoretical devel- opments are illustrated with experimental results.

Peer Reviewed