Implementation of Linear Controllers via Active Disturbance Rejection Control Structure

Linear active disturbance rejection control (LADRC) takes the controlled plant as a cascaded integral model and treats all other plant information and external disturbances as a generalized disturbance, and uses an linear extended state observer (ESO) to estimate the generalized disturbance and incorporates it in a linear state feedback control law to reject it quickly. This ESO-based LADRC controller is a fixed-structure controller as long as the (relative) order of the controlled system is specified. This article shows that any linear finite-dimensional controller can be implemented via the LADRC structure; thus, it is a general-purposed control structure in that it can be applied to any control system where linear control is sufficient. Case study shows that the implementation not only retains the disturbance rejection performance of the original linear controller but also improves its tracking performance due to the two-freedom-of-degree property of LADRC.