Active disturbance rejection control of Euler-Lagrange systems exploiting internal damping

Active disturbance rejection control (ADRC) is an efficient control technique to accommodate both internal uncertainties and external disturbances. In the typical ADRC framework, however, the design philosophy is to “force” the system dynamics into double integral form by extended state observer (ESO) and then controller is designed. Specially, the systems’ physical structure has been neglected in such design paradigm. In this paper, a new ADRC framework is proposed by incorporating at a fundamental level the physical structure of Euler-Lagrange (EL) systems. In particular, the differential feedback gain can be selected considerably small or even zero, due to an effective exploitation of the system’s internal damping. The design principle stems from analysis of the energy balance of EL systems, yielding a physically interpretable design. Moreover, the exploitation of system’s internal damping is thoroughly discussed, which is of practical significance for applications of the proposed design. Besides, a sliding mode ESO is designed to improve the estimation performance over traditional linear ESO. Finally, the proposed control framework is illustrated through tracking control of an omnidirectional mobile robot. Extensive experimental tests are conducted to verify the proposed design as well as the discussions.