A Study On Intelligent PID Control Of Ship Motion

The autopilots have played a very important role in ship maneuvering systems,which is the symbol of the property of ship steering. It has been one of the most important research topics of ship's maneuvering system,so a lot of experts and scholars have worked hard on it. But the conventional PID autopilot systems are lack of adapting to the ship dynamic property and the changes of sea environment, and they need to build up the mathematical model of ship. On the contrary,fuzzy control don't depend on the mathematical model of controlled objects and have the ability to adapt to the changes of system parameters, so it has the potential to overcome the drawbacks of conventional control schemes. The paper is developed under such engineering background.Control method for the early Bang-Bang control,PID control, and then for the adaptive control,optimal control,robust control, nonlinear control,up to now the study of intelligent control. These control methods are applied to the ship course control study, and has formed a PID autopilot,adaptive autopilot and other products,but because of the complexity of ship maneuvering, and that the dynamic characteristics of the ship features of a large inertia, large time-delay, and non-linear, the change of speed and load causes the model parameter perturbation; because of the additional power dynamically caused by the wind,drift of the ship's position caused by the current, the additional high-frequency vibration and low-frequency drift of the angle caused by the waves,the changes of conditions,the interference of environmental parameters and the non-precision of measurements, the ship dynamically has uncertainties in the voyage. And traditional control methods can not effectively control the unmodeled dynamic system, thus the effect of the autopilot control is declined. In order to solve the above problems, the further introduction of intelligent control techniques in autopilot technology is necessary. This article uses the combining of PID and fuzzy control method,in order to adapt to the requirements of ship motion control. First of all,the development of ship control technology and intelligent self-adaptive control technology and the tuning method of PID controller parameters are reviewed. In this paper,ship's mathematical model is researched,in consideration of,the forsces and moments from the environmental disturbances, such as winds, waves, currents, etc. According to nonlinear, time-varying and time-delayed parameters of ship course,the fuzzy controller was first designed based on the analysis of the fuzzy control theory, which is the basis of other high-level controllers. This kind of controller is easy to design and operate,and has improved convergence rates and less over shoot than PID controller,but has stable error. In order to improve the properties of the fuzzy controllers,a fuzzy-PID controller was designed respectively based on the fuzzy controller. The PID parameters on-line by using fuzzy set theory to improve the self-adaptive ability and to realize non-error control.At last,the simulation curve was given,and which show that the desired results were attained.