In this paper, a novel nonlinear robust controller ensuring time-varying output constraints for the double-rod hydraulic servo systems in the presence of largely unknown matched and mismatched disturbances is proposed. By employing two extended state observers for each channel of the load dynamics and pressure dynamics of the considered hydraulic system, the large matched and mismatched disturbances are successfully compensated. In addition, a time-varying barrier Lyapunov function (BLF) of asymmetric type has been employed to make sure that the position output is never violated. The resulting controller is synthesized using the backstepping procedure. The stability of the whole closed-loop hydraulic system associated with the dual extended state observer (ESO)-based controller is strictly guaranteed. In theory, the proposed control strategy can not only ensure the output satisfy the preset constrained space, but also enhance the output tracking performance when the system faces various largely unknown disturbances. The effectiveness of the proposed controller has also been demonstrated via comparative simulation results.
Rejection of mismatched disturbances for systems with input delay via a predictive extended state observer
