Further Improvements Of Fuzzy Track Keeping Controller For Ships

In order to solve the difficulties that the Line of Sight guidance algorithm decouples with navigation practice and poor steering performance when ships are at large steering angle,in this paper,the track keeping controller uses the LOS algorithm as the guidance algorithm and fuzzy control as control strategy,to design a track keeping controller which has the characteristics of good control performance,low steerage frequency and strong anti-interference ability.The LOS algorithm improved by N.Khaled could control the ship's track to approach the set route stably.However,because its ahead steering distance is a fixed value,the controller cannot make appropriate amount of advance.After many experiments,Xiao Qikui summarized a new ahead steering distance,which can make the controller complete track-keeping control tasks basically.But,there also are some aspects need to be improved.Based on the navigation practice,ship's steering is in close relationship with the maneuverability indices K,T,speed and steering angle.So,the author applies the ahead steering distance which is determined by the maneuverability indices K,T,speed and steering angle.It makes control algorithm adapt to more ship's steering characteristics.After a number of simulation tests,the author finds there always exists floating phenomenon when ship is at a large steering angle.So the author proposes a steering strategy,supposing two virtual turning points to guide the ship to complete the track keeping control task when ship is at a large steering angle.Simulation results show that the final fuzzy track keeping controller has the characteristics of small trajectory tracking error,small floating and low rudder angle amplitude when ship is at a large steering angle.The author uses the VISUAL BASIC 6.0 to achieve the playback of the simulation ship's motion and simulate the ship's motion.