Structure influence on the robust stability of linear active disturbance rejection control system

In this paper, the robust stabilities of linear active disturbance rejection control (LADRC) systems with different structures are studied. Firstly, 4 kinds of extended state observers (ESO) with different orders and inputs and 4 kinds of feedback control laws with different inputs are designed for a general second-order model. Then a necessary and sufficient stability criterion for the closed-loop system is derived from μ analysis. Based on the criterion, the maximum allowable bound of model parameter uncertainties can be got by solving a search problem. Analysis results of 9 kinds of LADRC systems with the same ESO bandwidths and same feedback control parameters show that low order ESOs and state feedback control laws are helpful to improve the stability of the closed-loop system in the presence of structured model uncertainty.