Multirate repetitive control and applications

In this paper, two multirate repetitive controllers are proposed, namely, repetitive intersample disturbance rejection (RIDR) and repetitive perfect tracking control (RPTC). First, in order to develop RIDR, multirate intersample disturbance rejection algorithm is reviewed which was proposed by authors for general digital control systems with restricted sampling frequency. Second, RPTC method is proposed to reduce the computation cost for system with many disturbance modes, in which the multirate control is introduced to overcome unstable zero problem of discrete-time plant. Third, both for RIDR and RPTC, the novel scheme of repetitive feedforward control is proposed based on switching mechanism, which enables the rejection of periodical disturbance without any sacrifice of the closed-loop characteristics. Finally, the proposed methods are applied to high-order repeatable runout (RRO) rejection problem of hard disk drive (HDD) and high-speed motion tracking problem of visual servoing. The advantages and disadvantages of these approaches are demonstrated through simulations and experiments.