Heading Control of ROV ROSUB 6000 using Non-linear Model-aided PD approach

A non-linear model-aided PD approach for implementing heading control algorithms in the 6000 m depth rated Remotely Operated Vehicle (ROSUB 6000) has been developed by National Institute of Ocean Technology, India is presented in this paper. ROSUB 6000 is developed for carrying out gas hydrate surveys, poly-metallic nodule exploration, deep water interventions, bathymetric surveys and salvage operations. A proper hydrodynamic model is required in the design of efficient guidance, navigation and control systems of ROV. Hydrodynamic modeling normally involves determination of added mass and drags coefficients from basic principles or scaled down models which are prone to inaccuracies. The proposed methodology makes use of vehicle onboard sensors and thrusters for identifying the vehicle hydrodynamic model parameters. This method is best suited for variable configuration ROV, where payload and shape changes with the mission objective. Experiments have been carried out to identify the hydrodynamic parameters in heading degree of freedom (DOF). The values are implemented in the model-based control algorithm aided by PD control. The heading control loop is found to perform with a heading maintenance with accuracy better than 2 deg. in the test environment. The closed loop heading motion is found to have a time constant of less than 30 seconds. Keywords— Dynamic modeling, Hydrodynamic modeling, ROV, ROV Cybernetics, Underwater heading control.