Active disturbance rejection control: Theoretical perspectives

This paper articulates, from a theoretical perspective, a new emerging control technology, known as active disturbance rejection control to this day. Three cornerstones toward building the foundation of active disturbance rejection control, namely, the tracking differentiator, the extended state observer, and the extended state observer based feedback are expounded separately. The paper tries to present relatively comprehensive overview about origin, idea, principle, development, possible limitations, as well as some unsolved problems for this viable PID alternative control technology.