Improved disturbance observer based control structure

This paper proposes an improved disturbance observer (DOB) based control configuration for non-minimum phase plants. The method introduces a high-pass filter in parallel with the plant. The filter is designed so that the parallel connection with the plant becomes of minimum phase. In the proposed control structure not only the output of nominal performance controller but also the feedback signal of system output are compensated by adding the another two controllers. Thus, the influences of the external disturbance and the measurement noise on the system output could be eliminated. Then, we discuss the internal stability and robust stability of this whole control system. At last, the design method of the high-pass filter is also given.