Abstract: In order to improve the disturbance rejection performance of electro-hydrostatic actuator (EHA) of ship rudder, a fusion control method based on linear active disturbance rejection control (LADRC) and fractional order PD control (FOPD) is proposed. The mathematical models of the drive motor and hydraulic system are established respectively. On this basis, linear extended state observer (LESO) is employed to estimate the total disturbances of EHA under different operating conditions, including internal and external disturbances. The bounded stability of LESO is also proved. Furthermore, fractional order PD control is used as the control law to actively suppress the estimated total disturbance, and the control parameters are determined by frequency response indicators such as shear frequency and phase margin. The joint simulation analysis of the EHA model based on AMESim and Simulink shows that the position control accuracy of the proposed control method based on LADRC and FOPD is about 1mm when the ship speed is 6kn or 8kn. The self-developed EHA is used to build the semi-physical testing device, on which the reverse rudder and sudden reversal tests are carried out. The results show that the proposed control method has good speed and stability in tracking steering commands under load disturbances and sudden reversal situations.

Key words: ship rudder, electro-hydrostatic actuator, linear active disturbance rejection, fractional PD