Experimental Validation of Underwater Depth and Orientation Control Using Reversible Fuel Cell Electrolysis

In this article, we present the experimental validation of our previous research on buoyancy control devices (BCDs) that are based on proton exchange membrane (PEM) electrolysis. These devices are used to control the buoyancy and orientation of autonomous underwater vehicles by volume adjustments of the output gases (hydrogen and oxygen) from PEM electrolysis. Two different devices are designed. Using the first device, we performed experiments to demonstrate the effectiveness of using regular (hard) thrusters and (soft) PEM electrolysis for depth control. We utilized a model predictive control law for this purpose. The experimental results showed that the addition of the soft actuator brings a significant amount of energy savings. Furthermore, we designed a second device to validate the simultaneous control of the depth and orientation of BCDs that use only PEM electrolysis. Two different closed-loop controllers are designed to use two PEM electrolyzers. The experimental results demonstrated their ability to control both vertical movement and orientation simultaneously. A feasibility study on deep ocean application has been conducted and simulation results have shown that an industrial PEM-based BCD can save up to 90% of energy when an underwater vehicle operates a payload of 5 kg under 300 bar water pressure.