Vibration suppression and optimal repetitive disturbance rejection control in semi-Nyquist frequency region using multirate sampling control

Multirate feedback controllers are proposed for digital control systems with relatively long sampling period. The proposed controllers achieve vibration suppression and disturbance rejection even in the semi-Nyquist frequency region. First, the continuous-time vibration suppression controller is exactly discretized by the multirate sampling control based on the closed-loop characteristics. Second, multirate repetitive controllers are proposed both by the feedback and feedforward approaches. Moreover, the inter-sample disturbance rejection performance is optimized by the fast sampling approach. The proposed controllers are applied to the settling and following modes of hard disk drive, and the advantages of these approaches are demonstrated by simulations.