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An enhanced repetitive control algorithm using the structure of disturbance observer

In repetitive control, the enhanced servo performance at multiple repetitive frequencies is usually followed by undesired error amplifications at other frequencies. This paper presents a new structural configuration of the internal model principle in repetitive control, wherein designers have more flexibility in the repetitive loop-shaping design, and amplification of non-repetitive errors can be greatly reduced. The proposed algorithm is particularly advantageous when repetitive control is required in environments where large amounts of non-repetitive disturbances exist. Verification of the algorithm is provided in a benchmark regulation problem of hard disk drives.