Robust course control for air cushion vehicle via novel sigmoid function differential disturbance observer

As a special device of air cushion vehicle, cushion system can reduce sailing resistance deeply so as to obtain higher speed. The main drawback is that sideslip phenomenon occurs easily, especially in the turning process. To solve this problem, a robust course controller for ACV is designed based on terminal sliding mode control method. The designed controller is more effective under the influence of sideslip angle than the before heading controller. A novel sigmoid function differential disturbance observer (SFDDO) is proposed. The designed SFDDO can accurately estimate system states, uncertainties and environment disturbances in finite time. Moreover, it can track first and second order derivatives of a bounded integrable function to simplify the derivative calculation and the structure of designed controller. The effectiveness and robustness of the control method is verified by simulations.