Abstract
The deep-sea autonomous underwater vehicle (AUV) is equipment of vital importance for ocean exploration, monitoring, and surveying. With a variable buoyancy system (VBS), AUV can achieve rising, diving, and hovering in the water column. This paper proposes a deep-sea AUV with an oil bladder type hydraulic VBS, which controls the oil flow rate with a proportional valve. However, the implementation of accurate depth control for AUV faces various challenges due to the varying water density with depth, the non-linear feature of the hydraulic system, and the disturbance from sea flows and currents. To tackle these problems, a third-order linear active disturbance rejection controller (LADRC) and its fuzzy adaptive version were designed and implemented in MATLAB/Simulink based on the state-space function of the proposed AUV system. Compared with the conventional PID controller, the simulation results indicate that the proposed LADRC controller shows strong robustness to disturbance, with other advantages including smaller steady-state error, overshoot, settling time, and response time. Moreover, the proposed fuzzy LADRC controller could further decrease the overshoot caused by the increasing target distance. The results prove that the designed depth controllers can meet the control requirements of the proposed deep-sea AUV.
Highlights
Academic Editors: Zheng Chen andThe ocean contains abundant resources and is of much research value [1]
The simulation results indicate that in the depth control of the autonomous underwater vehicle (AUV) without disturbance, the performance of the active disturbance rejection control (ADRC) type controllers is significantly better than the conventional proportional integral and derivative (PID) controller
This paper proposes a deep-sea AUV with oil bladder type variable buoyancy system (VBS)
Summary
The ocean contains abundant resources and is of much research value [1]. With the continuous exploration of the ocean, humans have made many discoveries leading to significant achievements [2,3]. There are three main types to change buoyancy: mass discarding, ballast water, and oil bladder [9]. To overcome external water pressure [15], the ballast water VBS requires a complex valve system and a high-pressure seawater pump [16], which results in structural complexity It is commonly used as the main VBS for most HOVs, like Shenhai Yongshi [17]. VBS is a closed system whose total mass is unchanged It adjusts the drainage volume of the vehicle by pumping oil in or out of an external flexible bladder. In [26], a hybrid oil bladder VBS with a passive accumulator was developed for deep-sea gliders, which can effectively utilize the ocean pressure differential energy to realize buoyancy compensation. Due to the advantages of oil bladder VBS, this paper proposes a deep-sea AUV using an oil bladder VBS with an electro-hydraulic proportional valve to achieve high depth control performance
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