In this note, we apply the proportional integral observer to simultaneously estimate system states and unknown disturbances for discrete-time nonminimum phase systems. Conditions for providing the existence of such observer are given. When the disturbances do not vary too much between two consecutive sampling instances, the proposed method can render the estimation errors of system states and disturbances to be constrained in a small bounded region. Simulation results support the theoretical developments.
For linear multiple input multiple output (MIMO) systems with mismatched parameter uncertainties and matched nonlinear perturbations, a compensator‐based controller based on the disturbance estimation algorithm is considered in this paper. We design a reduced‐order high‐gain observer to estimate the effect of matched perturbation, and introduce the estimation information into the controller design. Using singular perturbation theory, the proposed control law can guarantee robust stability of the closed‐loop system. Moreover, the peaking phenomenon in the control input during the transient time can be effectively avoided using our method. Finally, the feasibility of the proposed method is illustrated by a numerical example.
For mechanical systems using displacement measurements only, this study presents a dynamic compensator-based second-order sliding mode control algorithm without using any observer structure to estimate the velocity. Introducing the compensator into the sliding variable, a modified asymptotically stable second-order sliding mode control is developed. The proposed low-order dynamic controller inherently has low-pass filter property in which the effect of differentiators can be obtained. Using singular perturbation theory, the authors show that the system state is finally constrained in a small bound region when the gain is high enough. Finally, a numerical example is explained for demonstrating the applicability of the proposed scheme.
For a class of linear MIMO uncertain systems, a dynamic sliding mode control algorithm that avoids the chattering problem is proposed in this paper. Without using any differentiator, we develop a modified asymptotically stable second-order sliding mode control law in which the proposed controller can guarantee the finite time convergence to the sliding mode and can show that the system states asymptotically approach to zero. Finally, a numerical example is explained for demonstrating the applicability of the proposed scheme.
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