PIDA Control of Buoyancy Device Enabled by Water Electrolysis

In this article, a variable buoyancy system operated by water electrolysis with feedback depth control is developed. The system varies its buoyancy based on the collection of produced gases from water electrolysis and the release of these gases using solenoid valves. The system has advantages from the perspective of compact design and stealth because it does not need to carry pistons, motors, or air resources to control buoyancy force. Instead, it electrolyzes the freshwater surrounding the device with no noise. Further, since it is small and lightweight, the device facilitates smooth integration with other underwater robots for buoyancy control. A dynamic model is constructed for the buoyancy varying system. Then, a proportional-integral-derivative-acceleration feedback controller is designed to regulate the generation and release of gases to position and stabilize the device at a certain depth for the survey and data collection. Finally, the effectiveness of the controller is verified with simulations and experiments. The real-time experiment shows that the controller can stabilize the buoyancy device at any depth underwater with a settling time of 60 s for at least 5 min.