Abstract
This paper presents a novel nonlinear sliding mode control scheme that combines on-line model modification, a nonlinear sliding mode controller, and a disturbance observer to solve the essential problems in spacecraft electromagnetic docking control, such as model uncertainties, unknown external disturbances, and inherent strong nonlinearity and coupling. An improved far-field model of electromagnetic force which is much more accurate than the widely used far-field model is proposed to enable the model parameters to be on-line self-adjusting. Then, the relationship between magnetic moment allocation and energy consumption is derived, and the optimal direction of the magnetic moment vector is obtained. Based on the proposed improved far-field model and the research results of magnetic moment allocation law, a fast-nonsingular terminal mode controller driven by a disturbance observer is designed in the presence of model uncertainties and external disturbances. The proposed control method is guaranteed to be chattering-free and to possess superior properties such as finite-time convergence, high-precision tracking, and strong robustness. Two simulation scenarios are conducted to illustrate the necessity of modifying the far-field model and the effectiveness of the proposed control scheme. The simulation results indicate the realization of electromagnetic soft docking and validate the merits of the proposed control scheme. In the end of this paper, some conclusions are drawn.
Highlights
Spacecraft relative motion control using intersatellite electromagnetic interaction is a technical innovation and research hotspot in the field of spacecraft control
By designing a nonlinear sliding manifold, the terminal sliding mode (TSM) control was proposed and offers finite-time convergence and less steady-state errors [31]; there exist singularity problems. To avoid these singularity problems, a nonsingular terminal sliding mode (NTSM) controller which offers the advantages of linear sliding mode (LSM) and TSM was presented for coupled spacecraft docking in [32]
The improved far-field model, disturbance observer, and fastnonsingular terminal sliding mode (FNTSM) controller are combined and the model uncertainties and unknown external disturbances are considered, and a simulation is conducted to verify the effectiveness of the proposed control scheme
Summary
Spacecraft relative motion control using intersatellite electromagnetic interaction is a technical innovation and research hotspot in the field of spacecraft control. By designing a nonlinear sliding manifold, the terminal sliding mode (TSM) control was proposed and offers finite-time convergence and less steady-state errors [31]; there exist singularity problems To avoid these singularity problems, a nonsingular terminal sliding mode (NTSM) controller which offers the advantages of LSM and TSM was presented for coupled spacecraft docking in [32]. Based on the improved far-field model and optimal magnetic moment allocation, a global fast nonsingular terminal sliding controller driven by an exponentially convergent disturbance observer for electromagnetic soft-docking is designed. It is chattering-free and possesses superior properties such as global fast finite-time convergence, no singularity, strong robustness, and highprecision control.
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