Proposal of perfect tracking and perfect disturbance rejection control by multirate sampling and applications to hard disk drive control

Multirate two-degree-of-freedom controllers are proposed for digital control systems, where there is a restriction that the speed of the A/D converters are slower than that of the D/A converters. The proposed feedforward controller assures the perfect tracking at M inter-sampling points. Moreover, the proposed feedback controller assures the perfect disturbance rejection at M inter-sample points in the steady state. Illustrative examples of position control for hard disk drive are presented, and the advantages of this approach are demonstrated.