Underactuated Microsatellite Electromagnetic Docking Control Using Disturbance Observer-Based Sliding Mode Controller

This paper presents a novel control method that combines sliding mode controllers, disturbance observers and an exact robust differentiator to solve the underactuated microsatellite electromagnetic docking control problem, in which each docking satellite is equipped with only one single electromagnetic coil. The far-field model of electromagnetic force/torque is given and its model error is analyzed; and a six-degree-of-freedom (6-DOF) docking dynamics model using the far-field model is established. The generation method of the desired trajectory and desired attitude in the docking process is presented; and then an improved exact robust differentiator based on the 3rd-order sliding mode is proposed to produce the desired angular velocity and angular acceleration. In the presence of model uncertainties, external disturbances and input constraints, a disturbance observer-based sliding mode control scheme for underactuated microsatellite electromagnetic docking is developed. The whole closed-loop control system contains an inner-loop attitude controller and an outer-loop position controller. Numerical simulation results are presented to validate the effectiveness and the superior properties of the proposed control scheme.