Internal model control and disturbance observers

Internal model control schemes based on disturbance observers are analyzed and compared. It is shown that the proper choice of a filter and the possible use of an additional secondary feedback can give the various control structures the same performance and robustness. Theoretical analysis and examples indicate that a control scheme using a disturbance observer based on a model of the controlled system is the simplest one for applications where the controlled system includes an integrating process submitted to possibly constant disturbances at its input