A PID-backstepping Hybrid Position and Attitude Control of a Bi-copter AUV with a Moving Mass

This research aims to design a bi-copter AUV and evaluate its feasibility. Autonomous Underwater Vehicles (AUVs) that sail independently without cables and human operators are in the spotlight as an alternative to human divers. To miniaturize AUVs to operate in narrow spaces, we propose an AUV with two thrusters and two pitch angle servo motors: a 'bi-copter' AUV. The bi-copter is expected to be power efficient, and have high turning performance. However, precise and robust control performance is required to overcome its underactuated characteristics and disturbances. To enhance pitch motion stability, a Pitch Motion Compensator (PMC) with a Pitch Angle Disturbance Observer (PADO) is implemented and controls the position of a moving mass inside the AUV body. We propose a PID-Backstepping Hybrid (PBH) control composed of the PID position controller and the backstepping attitude (roll and yaw motion) controller for the position and attitude control. In addition, We propose the yaw angle reference value calculation methodology to control the y position indirectly. Our proposed method is evaluated by the simulations using MATLAB/Simulink and Simscape including wave disturbance and its feasibility is confirmed.