Compound Active Disturbance Rejection Control For Dynamic Positioning Of Semi-submersible Offshore Platforms

Dynamic positioning technologies are developing continuously with the development of exploring marine resources,and widely used in semi-submersible offshore platforms and ships.The pros and cons of control methods for dynamic positioning systems(DPSs)is crucial,however,semi-submersible offshore platforms are nonlinear and uncertain systems,resulting that there are no precise system models of them.At the same time,the interference of the marine environment is very complex,so people need to find more effective control methods to improve the dynamic positioning accuracy.Active disturbance rejection control(ADRC)is a kind of advanced control technology which developed in recent years.It has significant effect on the control of nonlinear systems and large delay controlled objects.However,there are still some drawbacks in ADRC,which need to be improved.Therefore,this thesis focuses on that introduce other control methods and ADRC to form composite active disturbance rejection control strategies,and apply them to the dynamic positioning field.The main contents are as follows:1.A three-degree-of-freedom low-frequency model of semi-submersible offshore platforms and the models of external wind,wave and current disturbance are discussed.In order to design controllers conveniently,the low-frequency model of platforms is transformed.And the simulation analysis is done to test whether the model is consistent with the general movement of the platform.2.This thesis introduces the basic principle of ADRC,and points out that ADRC is effective to control multivariable coupling systems.On this basis,the model of platforms is decoupled.In addition,the simulation analyses of PID control and ADRC are carried out on the dynamic positioning system of the offshore platform,then the advantages of ADRC relative to PID and the shortcomings of ADRC itself are expounded intuitively.3.Aiming at the shortcoming of the disturbance estimation ability of ADRC,a new type of continuous and smooth nonlinear function is introduced to improve the extended state observer(ESO).At the same time,non-singular terminal sliding mode control is used to replace the nonlinear state error feedback control law(NLSEF)to improve the response time and stability of systems.The effectiveness of the sliding mode active-disturbance rejection dynamic positioning controller is verified by simulation analyses,and the requirement is low to the thrust system and the economy is better.4.In order to improve the estimation ability of the dynamic positioning controller once again,the dynamic surface control is introduced to reconstruct the ESO.The simulation results show that,comparing with the traditional idea which introducing the continuous and smooth nonlinear function into the ESO,the dynamic surface extended state observer scheme can greatly improve the disturbanceestimation ability of the controller,The adaptive ability of the controller to the disturbance of the complex ocean environment is enhanced.