Disturbance Observer for Estimating Higher Order Disturbances in Time Series Expansion

In the note, a generalized disturbance observer capable of estimating higher order disturbances in the time series expansion is newly proposed. Initiated from a constant disturbance observer, we extend it systematically to cope with ramp disturbance and general order disturbances. The generalized form for disturbance observer exhibits the novel structure incorporating the system model and integrals. To be practical, the noisy measurement and the performance in the frequency domain are addressed. In addition, for a class of linear systems, an output-based disturbance observer of reduce order is newly derived from the proposed full state disturbance observer, and its potential applicability will be demonstrated by an example.

I. Introduction

For the past several decades, disturbance or unknown inputs observation has been one of major issues in the control engineering. In practice, it has gained the importance through various applications such as robot manipulator [1], [9], railway traction system [7], stabilization of magnetic bearing system [3], high speed XY stage [10], missile control [2], hard-disk drive system [18], pick-up control in optical data storage systems [11], [12], etc. Also, the disturbance observer is a key methodology for fault detection (e.g., see [15] and [22], among many).