Output feedback-based sliding mode control for disturbed motion control systems via a higher-order ESO approach

This study presents an output feedback-based sliding mode control approach for motion control systems with mismatched/matched disturbances. The key idea of this study is to reconstruct the unmeasured auxiliary states and disturbances synchronously online by constructing a higher-order extended state observer (HOESO). It is shown that the resulting sliding mode controller based on HOESO can drive the system output to an ultimately bounded region, which can be regulated arbitrarily small by assigning a sufficiently large scaling gain. Different from the existing extended state observer methods, the newly proposed HOESO treats the known dynamics satisfying the Lipschitz condition and the unknown higher-order disturbances separately. As such, it provides a feasible way for higher-precision states/disturbance estimation. Thanks to the utilisation of HOESO, the upper bound of disturbances is not necessarily required as a priori and the switching gain is adaptively chosen based on the estimation error such that the chattering effects can be significantly reduced. Experiments for speed regulation of a brushless DC motor are conducted to verify the effectiveness of the proposed method.