Reducing energy consumption in underwater vehicle hovering operations using a variable structure controller

Autonomous underwater vehicles and sensor platforms play a crucial role in the long-term monitoring of marine environments; however, their operational endurance is limited by energy constraints. Effective energy management is therefore essential, particularly with regard to actuation mechanisms, which are among the primary consumers of onboard energy. Consequently, control laws that reduce energy consumption while maintaining performance are of significant importance, as they contribute to more efficient energy utilization. The main contribution of this paper is the proposal of a novel depth control law that exploits the passive dynamics of buoyancy-controlled vehicles to save energy during hovering tasks. The proposed control strategy expends energy only in two situations: 1) to counteract conditions in which the system’s natural dynamics is detrimental to control objectives, and 2) to drive the system to rest when it is near the target depth. Both simulation and experimental results show that this approach reduces energy consumption compared to PID-based controllers and to recently reported energy-efficient strategies. Against the latter, the proposed method achieves energy savings of up to 13% while simultaneously reducing the average depth control error by 50%.