Research On Sliding Mode Control Of Dynamic Positioning System For Semi-submersible Ocean Drilling Platform

Semi-submersible offshore drilling platform is the main tool of deep-sea oil and gas exploration,and the accuracy and stability of its dynamic positioning system(DPS)is of great significance.Because the working environment of deep water semi-submersible offshore drilling platform is relatively complicated,which requires the high positioning accuracy.Then,the performance of platform control system will be directly related to the status and accuracy of platform dynamic positioning operation.Therefore,the dynamic positioning control system research is particularly necessary and urgent.Based on the semi-submersible drilling platform dynamic positioning process,seven different sliding mode control strategies are designed.The robust adaptive terminal sliding mode control algorithm and the sliding mode state observer are developed to the offshore drilling platform initially.The main work is as follows:According to the platform dynamic positioning system model and three basic assumptions: ? without model uncertainty,? without environmental interference,? system position signal and velocity signal can be measured.This paper designs a linear sliding mode controller SMC,a terminal sliding mode controller TSMC1 and a new terminal sliding mode controller TSMC2.Lyapunov method and simulation test show the stability of the system and the effectiveness of the controllers.By comparing the system’s response speed,robustness and disturbance suppression,the new terminal sliding mode control is the best one.According to the platform dynamic positioning system model,considering system uncertainty and interference from complex external environments,two kinds of controllers are designed by using the robust and disturbance suppression characteristics of sliding mode control: robust terminal sliding mode controller,robust adaptive terminal sliding mode controller.Firstly,a state feedback controller is designed to stabilize the nominal system.An adaptive terminal sliding mode compensator is used to eliminate the effects of uncertain dynamics and input disturbances in the second controller.Lyapunov method and simulation test verify the stability of the two control approaches.Its tracking errors are stabilized to zero in a finite time.The proposed approaches can effectively finish the dynamic positioning task in the presence of the wind,waves,flows and other complex high or low frequency interference.Most of the traditional controller designs are based on the assumption that the position and velocity can be measured.However,due to external interference and complex conditions in actual project,the velocity signal is difficult to be measured in real time.In view of this problem,two kinds of observer with filtering ability are designed: high gain observer and sliding mode observer,so as to estimate the velocity signal state properly.The Lyapunov method verifies the stability of the system.The simulation results show that the sliding mode controller based on state observation can realize the precise dynamic positioning and trajectory tracking control of semi-submersible offshore drilling platform.The velocity estimation issue is successfully solved when the offshore platform is working.