Abstract:

 A  ship’s straight-line tracking control system is a single-input and dual-output system. Due to the strong non-linearity and typical under-actuated properties, as well as the liability to wind, wave and current disturbance, the design of a ship’s tracking controller is  challenging work. In this paper, the mathematical model of a ship’s straight-line tracking control system was adopted and the ADRC(active disturbance rejection control technique)was also briefly introduced. The control scheme was accomplished by adding a tracking differentiator and the feedback control law comprised of the errors of the two-controlled variables, instead of  only one in the usual ADRC scheme. Compared to the usual ADRC calculation which is only suitable for single-input and single-output systems, this method expands the application range that the ADRC scheme can deal with. The simulation test results confirmed the validity of this method, showed the ADRC can acquire good dynamic performance,good steady performance, and excellent robust performance.

Key words:  ship, straight-line tracking control, ADRC, nonlinear control;underactuated system