In this paper, a composite control strategy is proposed to deal with output constraints and disturbances of the visual tracking system for an inertial stabilized platform, which combines active disturbance compensation and the variable gain function technique. Firstly, the model of system considering multi-source disturbances is established, where the controlled output is the constrained position of the target in the image plane. Secondly, in order to avoid the tracked target being lost in the field of view of the camera, a control method based on the variable gain function technique is designed to ensure that the controlled output remains within the feasible range. Moreover, the active disturbance estimation and compensation method is introduced to improve the anti-disturbance ability of the system under the situation of small output error, obtaining satisfactory tracking performance. The stability analysis and the proof of constrained output are given following the controller design. Finally, results of simulation and experiments are shown to illustrate the promised advantages of the proposed composite control approach.
The nonlinearities of piezoelectric actuators and external disturbances of the piezoelectric nanopositioning stage impose great, undesirable influences on the positioning accuracy of nanopositioning stage systems. This paper considers nonlinearities and external disturbances as a lumped disturbance and designs a composite control strategy for the piezoelectric nanopositioning stage to realize ultra-high precision motion control. The proposed strategy contains a composite disturbance observer and a continuous terminal sliding mode controller. The composite disturbance observer can estimate both periodic and aperiodic disturbances so that the composite control strategy can deal with the disturbances with high accuracy. Meanwhile, the continuous terminal sliding mode control is employed to eliminate the chattering phenomenon and speed up the convergence rate. The simulation and experiment results show that the composite control strategy achieves accurate estimation of different forms of disturbances and excellent tracking performance.
There are uncertainties and disturbances in the DC-DC buck converters system; in terms of actual working conditions, they are often very complex, exhibiting a polynomial form of time series. Therefore, a single controller and an observer that can only estimate slowly varying disturbances will lose their effectiveness. The generalized proportional integral observer can generally be used to estimate the disturbances in the polynomial form of time series, but it is usually necessary to select a high gain to achieve the fast convergence of the observer, which makes it sensitive to measurement noise. Therefore, before designing the controller that needs to estimate information, it is necessary to design a new structure that combines an observer and a Kalman filter. The filter is used for noise filtering, and the observer is used for the online reconstruction of disturbances. This can solve the above problems. Then, the whole control strategy is designed based on backstepping control. Theoretical analysis and experimental verification can effectively illustrate the feasibility and superiority of this strategy.
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