Abstract
In this paper, an adaptive discrete-time sliding mode control based on reduced-order disturbance observer is proposed for discretized multi-input multi-output systems subjected to unmatching condition. By using the designed discrete reduced-order disturbance observer, a new sliding surface is constructed to counteract the unmatched uncertainties. Then, to guarantee a smaller width of the quasi-sliding mode domain, an adaptive reaching law is developed, whose switching gain is adaptively tuned to prevent overestimation of disturbance on the premise of ensuring the reaching condition of sliding surface; meanwhile, the ranges of the quasi-sliding mode band and attractiveness region are deduced. The proposed control algorithm has low computational complexity and needs no information about the upper bound of unmatched uncertainty. The simulations on the control of a bank-to-turn missile demonstrates that the proposed method can effectively reject unmatched disturbance and provide higher accuracy in comparison with traditional methods.
Highlights
As an effective robust control technology, sliding mode control (SMC) has been widely investigated in theoretical research and extensively adopted in industrial application with advantages such as simplicity in implementation, guaranteed stability, and robustness against parameter variationsY
Based on virtual signal control technique, a fullorder terminal sliding mode (TSM) control was proposed to completely reject unmatched uncertainties and to force the output of multi-input multi-output (MIMO) systems to converge to equilibrium point in [9]
A new adaptive reaching law adopting a negative power term that contains the absolute value of sliding variable has been conducted in [17], and the control strategy ensures a small width of quasi sliding mode (QSM) band without jeopardizing the reaching time of sliding surface
Summary
As an effective robust control technology, sliding mode control (SMC) has been widely investigated in theoretical research and extensively adopted in industrial application with advantages such as simplicity in implementation, guaranteed stability, and robustness against parameter variations. A new adaptive reaching law adopting a negative power term that contains the absolute value of sliding variable has been conducted in [17], and the control strategy ensures a small width of QSM band without jeopardizing the reaching time of sliding surface These approaches are unable to reject unmatched disturbances. In [14], an adaptive TSM control was designed for nonlinear systems subjected to disturbances, in which it was not necessary to know the upper bound of disturbance Another newly popular DSMC, discrete-time integral sliding mode control (DISMC), has been reported to be an efficient scheme to reject unmatched uncertainties due to its simplicity and robustness [1, 27], but it brings some side effects such as large overshoot and nominal control performance degradation.
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