Realization of the inverse-model-based disturbance observer in the Luenberger-type observer form and its generalization

This paper gives the state-space representation of the inverse-model-based disturbance observer. The inverse-model-based disturbance observer proposed by Ohishi et al. estimates the disturbance with the inverse model of the plant and a low-pass filter and cancels out the effect of the disturbance with the estimated disturbance. Generally, for non-minimum phase plants, the inverse-model-based disturbance observer is constructed with an approximate stable inverse model or adding a parallel filter. Furthermore, the inverse-model-based disturbance observer is commonly discussed with the transfer function, and the relation between the Luenbergar-type observer is not clear. This paper gives the state-space representation of the inverse-model-based disturbance observer in the Luenberger-type observer form. Furthermore, this paper focuses on the characteristics of the systems for estimating the disturbance and shows the conditions for the Luenberger-type observer to be a disturbance observer. The Luenberger-type disturbance observer that satisfies the condition can be used for non-minimum phase systems since it does not use the inverse system model.