On Relationship Between Time Domain and Frequency Domain Disturbance Observers and Its Applications

Abstract

This paper provides a generic analysis of the relationship between timeand frequencydomain disturbance observer (DOB) design methodology. It is discovered that the traditional frequencydomain DOBs using a lowpass filter with unity gain can only handle disturbances satisfying matching condition, while the traditional timedomain DOBs always generate an observer with a highorder. A functional disturbance observer (FDOB) is proposed to improve the existing results together with its design guideline, frequency analysis, and existence condition. Compared with the existing frequencydomain DOBs, the proposed FDOB can handle more classes of disturbances, while compared with the existing timedomain DOBs, the proposed FDOB can generate an observer with a lowerorder. Numerical examples are presented to illustrate the main findings of this paper including a rotary mechanical system of nonminimum phase.