Linear active disturbance-rejection control (LADRC) is investigated in this paper. First, it is shown that LADRC structure can be changed to a two-degree-of-freedom (TDF) internal model control (IMC) structure, where the nominal model for the IMC design is simply a multiple integral plant, so analysis of LADRC can be done via the IMC framework. Then it is shown that the widely adopted bandwidth-tuning method for LADRC is equivalent to tuning the two time constants of the setpoint filter and the disturbance-rejection filter in IMC. Finally, to improve the control performance of an LADRC, a general method is proposed to incorporate extra dynamics of the controlled plant in LADRC.

General linear active disturbance rejection control (LADRC) is studied in the paper. First it is shown that there are some limitations in the conventional LADRC, and then some properties of general LADRC are analyzed. It is proved that any strictly-proper controller with integration can be implemented via a general LADRC, thus extends the application range of LADRC. Finally, a method is proposed to tune the general LADRC using the same bandwidth idea as the conventional LADRC.