Path Following Of Ship Based On Model Predictive Control

Three approaches based on model predictive control(MPC)and observer technology are proposed for the path following of under actuated ship with the model uncertainties,external environmental disturbances,unmeasured velocities,large inertia,rudder angle constraints and optimization.(1)Path following based on MPC: Designing an path MPC controller,the input rudder angle is calculated directly by the cross-track predictive errors.(2)Path following based on MPC and Line of Sight(LOS): A LOS guidance is used to design the reference heading,which converts path following into heading control.Then,designing a MPC heading controller,the rudder angle is calculated indirectly by heading predictive errors.(3)Path following based on MPC and Backstepping: A Backstepping is used to design the reference heading.Then,a MPC heading controller is used to design the rudder angle indirectly.The main contributions in this paper are as follows:(1)Embedding input rudder angle and control errors in MPC cost function,the performance between rudder angle and path following is balanced by adjusting weightings.This cost function is solved with input limits,so that rudder constraints are avoided.(2)The different state observers with simple structure and a few parameters are established,which can estimate ship velocities and the total unknowns including model uncertainties and external disturbances based on only position information.Moreover,the genetic algorithm is used to adjust extended state observer parameters online by predicting the future estimated errors,which could promote the estimate accuracy.(3)A variable acceptance circle radius and a variable virtual circle path near the reference waypoint are induced respectively,which the decrease of path following performance and the excessive rudder angle at the waypoint caused by the large ship inertia and the sudden across-track errors can be tackled.Finally,simulation analysis show that the designed controller can force ship to following the reference path successfully without knowing the velocity states and external disturbances such as wind,wave and current.Moreover,the rudder angle is small and smooth,the performances of MPC accuracy,observer estimation and path following are also promoted.These results may demonstrate the effectiveness of the proposed method.