Continuous adaptive sliding-mode control scheme for an autonomous underwater vehicle with region-based approach

Abstract

Set point method has been typically used for trajectory tracking of Autonomous Underwater Vehicle (AUV). However, this method has several limitations. In this regard, region based method has been applied in trajectory tracking of AUV in order to solve the limitations of set point method. The main idea behind the region-based method is the tracking target of an AUV set as a region, so that the AUV will maintain its position under weak ocean current. This method uses lower energy compared to set point method because the AUV will not turn on its thrusters as long as it maintains its position within the region. Realistically, there is also strong current that can drift vehicle away from the required region. The purpose of the thesis is to develop a robust controller with region-based method. Robust control enables an AUV to reject the disturbance and re-enter the region even under the influence of external disturbance. Based on the literature review, adaptive sliding mode control was chosen as the proposed controller in this study. Sliding mode control is known for its insensitivity towards uncertainty and external disturbance. Adaptive component was introduced to replace switching component. This substitute enables AUV to reject external disturbance better compared to conventional sliding mode control. The stability of the proposed controller was analyzed using Lyapunov function. The energy consumption of region based method was compared with the set point tracking method. It has been shown from this study that the energy consumption for region-based method is indeed lower than set point method. The effectiveness of the proposed controller was compared with adaptive controller using simulation under the influence of ocean current. Underwater vehicle model used in the simulation was Omni Directional Intelligent Navigator (ODIN). It has been proven that the proposed controller performed better compared to adaptive controller. The proposed controller had managed to handle ocean current and re-enter the region.