Disturbance observers: methods and applications. I. Methods

The survey is devoted to an exposition of the history of development and the current state of theoretical methods for constructing disturbance observers, whose appearance in control theory and practice dates back to the middle of the 1960s and is associated with the expansion of algebraic methods in controller synthesis, the emergence of computer-based synthesis procedures, the need to solve more and more complex problems, and the desire to optimize the control process. The survey describes observers of harmonic disturbances, outlines the internal model principle, considers observers of bounded disturbances, and describes methods for estimating disturbances using auxiliary filters in the form of transfer functions and state observers.