Active disturbance rejection control: Methodology, theoretical analysis and applications

Uncertainties widely exist in practice. This is one of the main reasons why control of systems with uncertainties is always a fundamental and challenging issue. Basically, the uncertainties stem from two sources: internal (parameter or unmodeled dynamics) uncertainties and external (disturbance) uncertainties. The paper first reviews the methods in the modern control theory, which were proposed for controlling of uncertain systems. These methods include the adaptive control, robust control, disturbance observers based control methods, output regulator theory for uncertain systems, active disturbance rejection control (ADRC), etc. Then the process of theoretical analysis for ADRC, mainly the convergence of the tracking differentiator (TD), the capabilities of the extended state observer (ESO) for estimating uncertainties and the closed-loop stability of ADRC, is introduced. Finally, some keys in the application of ADRC are discussed.