Research On Switched Control Of Dynamic Positioning Vessel

With the exploration and development of Marine resources,dynamic positioning has been widely used in all kinds of Marine operation vessels,and the roles played in the offshore development become more and more important.Vessels must be able to conduct continuously and steadily under the constantly changing ocean environment.Obviously,a single controller can't satisfy the control requirements of the ships under the changing sea state.Therefore,this paper proposes a switched control system used for dynamic positioning vessels under the changing sea state.The switched control system mainly uses fuzzy switching logic to add the outputs of the sub-controllers which designed in different sea states according to the corresponding output-weight values,and accordingly produces the control function,not only to improve the control precision of the system,but also to ensure the smoothness of the switch process between the sub-controllers in varying sea state.In this dissertation,the specific research contents as follows:Firstly,establish the low frequency motion mathematical model of the surface ship,and according to the first-order wave,ship's high frequency motion mathematical model is established.In order to better study the motion of surface ship,the corresponding model of the ocean environment disturbances(wind,wave and current)is established respectively.According to the established mathematical model of ship motion,a simulation was carried out on the research object of the ship,and verified the correctness of the established model to provide reliable basis for further research.Secondly,divide the sea states into the calm sea states,the moderate sea states and the high sea states,according to the significant wave height.In three typical sea states,according to the corresponding system model,design the corresponding nonlinear passive observer,and the simulation was carried out to verify the designed observer's correctness respectively.Then design the controller on the basis of the designed nonlinear passive observer in corresponding sea states.Use the conventional multi-output of PID controller under the calm sea states and moderate sea states,and the multi-output PID controller with acceleration feedback under the high sea states,and the effectiveness of the designed controllers was verified through the simulation according to the corresponding sea states.Finally,design the fuzzy supervisor based on T-S fuzzy model and the estimation of the wave peak frequency,and estimate the peak frequency of wave online by using the AR-model parameters estimation.The estimation of the wave peak frequency is used to make the real-time adjustment of the related parameters in the designed nonlinear passive observer under different sea states,thus forming the adaptive nonlinear passive observer.The fuzzy supervisor use the estimation of the wave peak frequency to add the outputs of the sub-controllers which designed in different sea states according to the corresponding output-weight values,so as to form a complete fuzzy switched control system of dynamic positioning.In order to verify the control effect of the fuzzy switch control system of dynamic positioning in constantly changing sea states,a comparative simulation was conducted between the single controller and the switched control system.The simulation results showed that the switched control system of dynamic positioning performed better than the single controller when the vessel was exposed to changes of ocean environmental conditions,and had a smooth transition process.