Complementary Control Allocation For Over-Actuated Depth Control In Underwater Vehicles

Some underwater vehicles utilize multiple types of depth actuators to achieve depth control to take advantage of desirable properties of each actuator in different situations. The Lagrangian Float developed at URI uses both a piston style variable buoyancy system (VBS) and a thruster to achieve depth control. The purpose of this work is to develop a single control system to intelligently balance actuation between the thruster and VBS that takes advantage of the properties of each actuator. A three part state feedback controller was developed. The controller calculates a control force, uses a pair of complementary filters to allocate the control, and translates the control forces into actuator inputs using actuator models. The filters were designed to apply low-frequency control inputs with the VBS and high-frequency control inputs with the thruster. The controller was tested both in simulation and in the field, and was able to provide a robust method of tracking reference trajectories while allocating the desired control between the two actuators