Optimal Trajectory Planning and Control of Buoyancy Control Device Enabled by Water Electrolyzer

Buoyancy control device (BCD) is an essential component for the underwater vehicle to achieve its vertical maneuvering. Previously, a proportional-integral-derivative (PID) controller was developed for a buoyancy device enabled by ionic polymer-metal composite (IPMC) water electrolyzer. With the help of a fluid pressure sensor, the buoyancy device can be stabilized at a specific depth. However, due to the slow gas generation rate, a transition period had to be added into the depth control in order to avoid saturating the control input to the IPMC electrolyzer. In this paper, to systematically obtain the transition period, an optimal trajectory planning is developed for the BCD with consideration of slow gas generation rate. An optimal trajectory is obtained by solving a bang-off-bang minimum time optimal control problem with the control input and velocity constraints. Then a state feedback tracking control is developed to track the optimal trajectory. Simulation results have shown that the BCD is stable during the tracking and the control input and velocity are always bounded within the allowable ranges.