Robust stabilization via disturbance observer with noise reduction

In this paper, we propose a robust controller using a modified disturbance observer (DOB). This modification is asked because the conventional DOB structure does not provide with any means to tune the high-frequency response. Since the measurement noise is significant in the high-frequency range, the performance against the noise in the conventional DOB control system cannot be better than that of the closed-loop system without DOB. Inspired by the new structure given in (Xie, 2010), we propose a modified disturbance observer structure, and present a necessary and sufficient condition for robust stability of the actual closed-loop system. Illustrative examples show the effectiveness of the proposed design.