A Novel Synthesis Method of Disturbance Observers for Estimating Biased Sinusoidal Disturbances

Abstract

In this paper, a novel synthesis method of disturbance observer which can asymptotically estimate a biased sinusoidal disturbance using the conventional disturbance observer is studied. The basic idea is to synthesize the disturbance observer gain matrix based on the following two considerations: 1) a zero located at the origin can be assigned to the closed-loop transfer function G_dd(s) from the disturbance to the disturbance estimation error, 2) all poles of G_dd(s) can be obtained in the complex left half-plane. The zero assignment of G_dd(s) can be accomplished using only one element of the gain matrix, and all poles of G_dd(s) can be assigned using the remaining elements of the gain matrix. The usefulness of the proposed method is verified by the angle control of a direct current(DC) motor system with the estimation performance of disturbances.