Depth control of an over-actuated, hover-capable autonomous underwater vehicle with experimental verification

A PI-D based control system is developed for over-actuated, hover-capable AUVs which enables a smooth transition from hover-style to flight-style operation. A system stability and convergence is proven using a Lyapunov-based approach. The performance of the controller is demonstrated by simulation but crucially is proven to provide satisfactory performance experimentally. The approach is able to operate over a range of vehicle ballasting configurations, and to imposed external disturbances. The proposed system is computationally inexpensive and does not require a detailed hydrodynamic model to implement. By monitoring the energy consumption on board, the cost of maintaining depth at a range of forward speeds with different buoyancy conditions can be quantified and their impact on cost of transport is highlighted for future optimisation of energy consumption