Modeling, characterization and control of a piston-driven buoyancy system for a hybrid aerial underwater vehicle

This paper proposed the design and stability analysis of a piston variable buoyancy system (PVBS) with integration to a hybrid aerial underwater vehicle (HAUV). The HAUV must be lightweight and maneuverable to have sufficient endurance and reliability of operating in both underwater/air environments. To meet this crucial requirement, we designed a highly compact and lightweight PVBS to regulate the vehicle orientation and depth while operating underwater. A nonlinear motion model is firstly formulated to study the stability and control strategy of the PVBS.Frequency response analysis shows that the PVBS is inherently unstable. Therefore, a computationally affordable PID controller with a preset piston position is further developed to improve its phase response and hence make the PVBS more stable with anti-interference loss. Performance comparison between PID controllers with and without a preset piston position was conducted with simulations based on the nonlinear motion model. The effectiveness of the controller on gliding motion with different linear actuator speed are discussed based on extensive simulations. Field experiments of the designed PVBS with application to a novel HAUV named Nezha III are conducted. Results illustrate that, with the PVBS, Nezha III is able to maintain a desired vehicle pitch and heave velocity, as well as perform stable sawtooth gliding motion.