A new disturbance observer for non-minimum phase linear systems

Motivated by the fact that the application of the disturbance observer (DOB) approach has been limited to minimum phase systems, we propose a new DOB configuration for non-minimum phase systems. The proposed configuration introduces a new filter, which corresponds to the Q-filter of the classical linear DOB, in a different place of the inner-loop. This new configuration enables an application of DOB idea to the non-minimum phase systems. After analyzing robust internal stability of the proposed configuration, we present a synthesis methodology of the filter based on the H_infin synthesis technique.