Semiglobal exponential control of Euler-Lagrange systems using a sliding-mode disturbance observer

Sliding-mode disturbance observer (SMDOB) is appealing for its ability in the estimation of system uncertainties and disturbances without introducing serious chattering in the sliding mode technique. However, existing SMDOB-based controllers with stability guarantee were analyzed by only considering disturbances or under a strict assumption that the time derivatives of system uncertainties are bounded prior to control implementation. This paper proposes a SMDOB-based tracking control strategy for Euler-Lagrange systems with modeling uncertainties and external disturbances. The SMDOB is designed by the construction of an extended state observer embedded by an improved super-twisting algorithm. Compared with existing SMDOB-based controllers, the significant advantage of the proposed controller lies in semiglobal exponential stability guarantee for the combined observer-controller system without the assumption that the time derivatives of modeling uncertainties are bounded by constants. The chattering caused by switching signals is alleviated by passing the switching signals through a low-pass filter in the SMDOB and is compressed by the frequency bandwidths of both the SMDOB and the control system. The effectiveness of the designed SMDOB-based controller is illustrated by simulations on a two-link robot manipulator. (C) 2019 Elsevier Ltd. All rights reserved.