Abstract: In order to improve the automation level and enhance the navigation safety of ships, stable control for ship speed is very important. Good control effect is difficult to obtain based on the conventional control method since the marine speed control system is a time-varying parameters and nonlinear complicated propulsion system. The uncertainty of the system parameters and the effect of environment such as winds, waves and currents were considered adequately in ship motion mathematical model with disturbing force. The mathematic model was linearized accurately with the differential geometry method. Then the nonlinear H_∞ controller was designed according to the linear H_∞ theory. The simulation results show that the H_∞ controller could effectively restrain the effect of the environment disturbance, improve the stability of the control system, ensure the accuracy of control and enhance the systems' robustness.

Key words: ship speed control, parameter perturbation, nonlinear H-infinity control, robustness