Feed forward filters for state and disturbance estimation

This paper introduces a method for representing an observer as a set of decoupled filters to provide an understanding of observer design for the practitioner. The concept uses feed forward information to predict and cancel phase lag inherent in common filters. A general modeling paradigm is also proposed to simplify disturbance rejection techniques. Both ideas are applied to analyze and compare approximate differentiators, state observers, disturbance observers (DOB), unknown input observers (UIO), and extended state observers (ESO).