Composite hovering control of underwater vehicles via variable ballast systems
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ORIGINAL ARTICLE
Composite hovering control of underwater vehicles via variable ballast systems Anyuan Bi1 · Zhengping Feng1,2 Received: 21 June 2018 / Accepted: 3 August 2019 © The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2019
Abstract In this paper, a composite hovering control scheme is proposed to improve the disturbance rejection performance of underwater vehicles via variable ballast systems (VBSs). A nonlinear disturbance observer (NDOB) based feedforward controller, which estimates and then compensates the resultant force of external disturbances, is augmented to the conventional proportional plus derivative (PD) based feedback control system. Both stability and convergence of the overall system have been guaranteed via Lyapunov analysis. Simulation results show that the NDOB based composite hovering control system exhibits more desirable performance in disturbance rejection than conventional PD control system. Keywords Underwater vehicles · Hovering control · Variable ballast systems · Nonlinear disturbance observer · Lyapunov stability
1 Introduction Due to the advantages of cost-effectiveness, mobility and ease in operation, underwater vehicles of various types have become indispensable tools for deep-sea exploration and exploitation such as inspection, sampling and so on. Refer to, for example [1–5], and references therein. With underwater missions becoming more varied and complex [6–8], high-performance motion control, especially hovering control, i.e., reaching or maintaining desired depths without forward velocity, is essential [9]. Several different hovering control schemes have been developed by researchers over the past few years. Model predictive control (MPC) is used to provide hoverability for an autonomous underwater vehicle with two vertical tunnel thrusters [10]. Sliding mode control (SMC) of a nonlinear system by input–output linearization is applied via a blowing/venting variable ballast system [9]. However, either accurate model for MPC [11] or exact bounds of parametric * Zhengping Feng [email protected] 1
School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Collaborative Innovation Center for Advanced Ship and Dee‑Sea Exploration, Shanghai Jiao Tong University, Shanghai 200240, China
2
uncertainty and disturbances for SMC [12] is required. Due to its independence on plant model, proportional plus derivative (PD) control has been widely used in various hovering control systems [13–16]. And for known vertical imbalanced forces, they can also be perfectly rejected by PD control [17]. Although underwater vehicles operating at deep submergence can be considered to be in a wave-free environment, which means vertical imbalanced forces caused by unknown and time-varying wave disturbances are not present, the imbalance of vehicle gravity and buoyancy, yet constant within small-scaled operation zones, could still be unknown a priori. This is due to the fact that the density of seawater varies signific
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