Robust periodic disturbance compensation via multirate control

Abstract

In this thesis, an adaptive feedforward cancellation (AFC) scheme based on multirate discretization is proposed for compensation of periodic disturbance in hard disk drive (HDD) digital servo systems. By discretizing the plant via multirate scheme, we obtain the inverse of the closed-loop transfer function no matter whether the closed-loop system is a minimum phase one or not. The proposed scheme cancels selected repeatable runout (RRO)components rapidly without amplifying unselected higher frequency harmonics. Simulation and experiment results show that the scheme can attenuate selected RRO harmonics efectively, even at around the open-loop crossover frequency range which cannot be achieved by the usual AFC scheme. The proposed scheme is also robust against plant parameter variations.