  The basic active disturbance rejection control (BADRC) algorithm with only
one order higher extended state observer (ESO) proves to be robust to both
internal and external disturbances. An advantage of BADRC is that in many
applications it can achieve high disturbance attenuation level without
requiring a detailed model of the plant or disturbance. However, this can be
regarded as a disadvantage when the disturbance characteristic is known since
the BADRC algorithm cannot exploit such information. This paper proposes an
internal model based ADRC (IADRC) method, which can take advantage of knowing
disturbance characteristic to achieve perfect estimation of the disturbance
under some mild assumptions. The effectiveness of the proposed method is
validated by comprehensive simulations and comparisons with the BADRC
algorithm.
