Adaptive Autopilot System for Small Ships Employing E-TOP Method and SOM

Abstract

A phase diagram of error and its derivative is useful to illustrate the state of the control system, where a fixed point at origin stands for a stable state, a point leaving origin an unstable state, a point moving round the origin an oscillatory state, etc. Thus the state of the control system is estimated by the motion of the point in the diagram. When the control system is under a strong or periodic disturbance, the state point moves round the origin staggeringly or periodically. It is difficult to evaluate the state of the control system in such conditions and the appropriate control is hardly realized. The E-TOP (evaluation with trajectory on phase diagram) method, presented by the authors, facilitates extracting the feature parameters from the trajectory in the phase diagram. The feature parameters characterize the behaviour of the control system. The adaptive PID autopilot system employing the E-TOP method is very efficient to evaluate the behaviour of small ships, the attitude of which is easily varied by the waves. However, when the attitude of the ship body is strongly staggering, the adaptive autopilot system cannot work appropriately. To cope with this problem, we propose the advanced E-TOP adaptive PID autopilot system, which employs the self-organizing maps (SOM)[2]. The advantage of this autopilot system to the conventional one is shown by the software simulation.