OUTPUT FEEDBACK TRACKING CONTROL OF SURFACE SHIPS K.D. Do and J. Pan Department of Mechanical and Materials Engineering The University of Western Australia, Nedlands WA 6907, Australia Email: duc@mech.uwa.edu.au Abstract: A controller is developed to make surface ships track a reference trajectory using only position and heading measurements for feedback under the environmental disturbances. The controller is first developed for full state feedback. A nonlinear dynamic filter, which is fundamentally different from the linear and high gain filters used in literature, is then designed to construct surge, sway and yaw velocities. The solution utilizes several properties of the ocean surface ships. Numerical simulations on a monohull ship with the length of 32 illustrate the effectiveness of the proposed controller. Copyright @ 2002 IFAC Keywords: nonlinear control, surface ship, output feedback, tracking. 1. INTRODUCTION Measurements of the ship velocities for most ships are not available and often corrupted with noise. Therefore, for feedback ship control systems, ship velocities need to be computed from position and heading measurements. In conventional feedback ship control systems, the ship velocities are often estimated by using Kalman filter. The nonlinear ship model is linearized around the operating points. A typical example is the linearization of the kinematic equations of ship motion about a set of 36 constant yaw angles separated by 10 degrees in order to cover the whole operating area of 360 degrees. For each of these linearized models, Kalman filters and control gains have to be computed and then modified on line using gain scheduling techniques. Although some acceptable results have been achieved the aforementioned linear control systems have certain drawbacks. They are developed based on linear models while the ship motion dynamics are inherently nonlinear. The useful nonlinearities are not utilized in the control design. They require a considerable amount of tuning work. The ad hoc nature of the linearization approach does not guarantee the desired stability and convergence properties, which mean a poor performance of the closed loop system. The problem of output feedback, i.e. only position measurements are available for feedback, control of surface ocean vessels has been a topic of considerable interest since velocity measurement sensors are often contaminated with noise and are expensive. However the previous work targeted at the output feedback control problem to achieved global results was only devoted to dynamic positioning of ships (see Fossen (2000), Fossen and Grovlen (1998), Aarset et al. (1998)). In these works, the square term of velocity due to the Coriolis matrix was ignored since the vessel operates at low speed in dynamic positioning. Then several types of observer were designed to estimate vessel velocities in surge, sway and yaw. A common feature of the proposed output feedback controller for dynamic positioning is that the observers are first designed such that the observer error is asymptotically stable then the control inputs are designed by using the information from the observers. The output tracking control of surface ships in one degree of freedom has been addressed in literature. Paulsen et al. (1998) derived a passive control law Copyright © 2002 IFAC 15th Triennial World Congress, Barcelona, Spain