Objective In order to solve such problems as the large rudder angle output, high steering frequency, slow control speed and low control accuracy of controllers when ships sail at sea, a third-order closed-loop gain shaping algorithm is used to design a robust controller.

Method First, the linear robust controller is designed using the third-order closed-loop gain shaping algorithm, and hyperbolic tangent nonlinear modification and a zero-order holder are added to the control strategy. The performance of the controller is then simulated under different sea conditions.

Results  As the results show, compared with the traditional PID controller based on nonlinear modification, the proposed controller has improved delay time, control accuracy and energy output by 36%, 14% and 32% respectively under general sea conditions, and improved delay time, control accuracy and energy output by 27%, 7% and 16% respectively under heavy sea conditions. In addition, the simulation results of the controller under different sea conditions show stable rudder angle output and the ability to stabilize near the critical value quickly, proving that it has good robustness.

Conclusion The improved controller is in line with engineering practices and has good application reference value for the control of intelligent ships.