UDE-based robust control for systems with mismatched uncertainties via feedback compensation

The uncertainty and disturbance estimator (UDE)-based robust control is extensively investigated for its merits of strong robustness and straightforward principle. However, the structural constraint of UDE-based control limits its application to systems with matched uncertainties. In this paper, an improved UDE-based robust control strategy is proposed to address mismatched uncertainties so that it can be applied to systems with both matched and mismatched uncertainties. A modified reference model is designed with the feedback compensation of the estimated mismatched uncertainties. Besides, the estimated matched uncertainties are adopted for the feedforward control, as a compensation term of the robust control law. Moreover, the stability analysis and steady-state performance of the closed-loop system are presented. Simulations on a magnetic levitation system are carried out to illustrate the effectiveness and superiority of the proposed control scheme, which achieves robust stability and zero steady tracking error in the presence of both matched and mismatched uncertainties.