An Internal Model Control Approach to the Design of Adaptive Ship Steering Autopilot

• Main Authors: Lin, Kang Fu, 林港富
• Other Authors: Lee Tai-Shen
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/09350237958788922198

碩士 === 國立海洋大學 === 航運技術研究所 === 86 === Abstract-This paper is concerned with the design of an adaptive ship steering autopilot. Specifically, an Internal Model Control(IMC) design method is coupled with a recursive least- squares method in forming the adaptive autopilot. The IMC design method is very attractive from the viewpoint of its relative easiness in satisfying the nominal internal stability conditions. A second order Nomoto model is taken as the ship model in the controller design. The autopilot obtained with the IMC design method is equivaa 2nd order PID type controller. Moreover, the proposed IMC design method offers explicit formulas relating the autopilot gain coefficients to the ship model parameters and a design parameter that determines the speed of response of the system. A recursive least-squares method is employed in estimating the ship model parameters under various operating conditions, and then the autopilot gain coefficients can be determined accordingly. This allows the autopilot to adapt to changing operating conditions. To avoid instability phenomenon caused by rudder saturation and rudder rate limitation, a reference conditioning technique is employed to bring the rudder limit and rudder rate limit into the adaptation design consideration. Specifically, the reference signal is modified such that the rudder input command is always consistent with the actual rudder input supplied by the actuator. That is, the controller uses the full power of the steering machine whenever necessary, without pushing the steering machine to the nonlinear saturation and slew rate limitation boundaries indefinitely. This so-called anti-windup consideration is really necessary, since the wind-up problem is much serious in adaptive control than in standard controller with constant gain. Computer simulations indicate that the proposed adaptive autopilot achieves satisfactory course- changing maneuvers while sailing through waters of different depth.