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A nonlilear controller for ship autopilots

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In this paper, a nonlinear optimal control law based on aggregated variables is presented. The criterion is chosen so that the dynamic characteristics of object are included. The stability of the closed-loop system is global according to the Lyapunov stability theory. The control law depends explicitly on ship model parameters, so that it is can be easily to tune when the parameters change. | Vietnam Journal of Mechanics, VAST, Vol. 34, No. 3 (2012), pp. 203 – 210 A NONLILEAR CONTROLLER FOR SHIP AUTOPILOTS Le Thanh Tung Hanoi University of Science and Technology, Vietnam Abstract. Conventional ship autopilots are designed based on a linear ship model using pole - placement technique or linear optimal theory. However, in operation, the ship kinematical parameters can go out the linear limits. In this paper, a nonlinear optimal control law based on aggregated variables is presented. The criterion is chosen so that the dynamic characteristics of object are included. The stability of the closed-loop system is global according to the Lyapunov stability theory. The control law depends explicitly on ship model parameters, so that it is can be easily to tune when the parameters change. Key words: Ship autopilot, nonlinear control, aggregated regulator, aggregated variable. 1. INTRODUCTION Conventional ship autopilots are designed based on a linear ship model using pole - placement technique or linear optimal theory without considering steering dynamics. However, in operation, the ship kinematical parameters can go out the linear limits; the steering mechanism has limit speed of deflection. In such a case the stability of the closed loop system may not be guaranteed. More ever, neglecting the nonlinearity and dynamics of steering machine may effect on system performance, usually reduces it. For a nonlinear system the back stepping or state feedback linearization techniques can be used [1, 2], but no optimal criterion is considered in these approaches. In this paper, a nonlinear optimal control law based on so - called aggregated variables is presented. The criterion is chosen so that the dynamic characteristics of object are included. The stability of the closed loop system is global according to the Lyapunov stability theory. The control law depends explicitly on ship model parameters, so that it is can be easily to tune when the parameters change. The .