This paper deals with the finite time stability and control for a class of uncertain variable fractional order nonlinear systems. The variable fractional Lyapunov direct method is developed to provide the basis for the stability proof of the system considered. The sliding mode control method is applied for robust control of uncertain variable fractional order systems; furthermore, the chattering phenomenon is avoided. And the finite time stability of the systems under control law is proved based on the proposed stability criterion. Finally, numerical simulations are proposed and the efficiency of the controller is verified.
This paper investigates the problem of rotation matrix-based attitude synchronization and tracking control for spacecraft formation flying exposed to external disturbance and unknown inertial matrix. For the purpose of ensuring finite-time convergence for attitude tracking errors, a hyperbolic tangent function-based sliding mode surface is designed. Based on the sliding mode variable, an adaptive law is proposed to estimate the upper bound of unknown disturbance and radial basis function is employed to approximate unknown system dynamics. The minimum learning parameter algorithm is adopted to reduce the computational burden. It is demonstrated by Lyapunov-based analysis that the sliding mode surface and estimating errors will possess finite-time stability under the presented controller. Finally, results of numerical simulations are exhibited to validate the stability and validity of the proposed controller. INDEX TERMS rotation matrix, finite-time coordinate control, spacecraft formation flying, sliding mode, neural network
This paper concerns the control algorithm oriented to nonparallel-ground-track-imaging for agile optical satellite. Firstly, for obtaining the desired trajectory, the mapping relationship between the satellite attitude and the ground stripe is established by using space vector method. According to the mapping function, an attitude adjustment strategy via constant scanning velocity is proposed. Then, considering the exact information of the external disturbance cannot be obtained and the input saturation problem, a robust anti-saturation tracking controller is designed via fixed-time disturbance observer and integral sliding mode. Finally, the effectiveness of the proposed control algorithm is illustrated by numerical simulation. INDEX TERMS Agile optical satellite, nonparallel-ground-track-imaging, integral sliding mode, disturbance observer, input saturation.
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