Robust design of repetitive control system

Repetitive controller is usually designed by assuming constant period of reference/disturbance signal, which leads to the selection of fixed sampling period. However, in practical, reference signal and disturbance are varying in period. Therefore, sampling period is carefully adjusted to overcome period variation, which makes characteristic of the plant is also changing. Robust design is employed to obtain pre-compensator which stabilizes closed loop repetitive system for all values of sampling period in the known interval. The design consists of two steps; constructing a nominal pre-compensator and designing robust pre-compensator which works well for large range of sampling period variation. In the design, time-varying plant parameters due to sampling period variation are treated as parametric uncertainties. The new form of pre-compensator which works with this robust design is also proposed.