Reformulation of Disturbance Observer design in the frequency domain

This paper presents a simple controller design methodology in the frequency domain for disturbance rejection specifications. It captures the main characteristics at low and high frequencies of a Disturbance Observer Based Control, and solves some of their principal drawbacks in terms of stability and performance specifications, quantifying the inherent limitations for disturbance rejection by means of the available phase. The new technique is applied in the control system of two applications: a hard disk drive and a servo-system position control.