Double-Loop Sliding Mode Controller with An Ocean Current Observer for the Trajectory Tracking of ROV

Yuxue Wang,Guijie Liu,Hailiang Sun,Weilei Mu

doi:10.3390/jmse9091000

Abstract

To solve the trajectory tracking problem of insufficient response and the large tracking error of remotely operated vehicles (ROVs) under the interference of large ocean currents, this paper proposes a double-loop sliding mode controller with an ocean current observer. The designed controller consisted of an outer-loop controller (the position controller) and an inner-loop controller (the velocity controller): the outer controller was designed by the position error, and a reference velocity was created for the inner loop to achieve accurate positioning and attitude tracking. The reference control input was treated as a new target to design the inner-loop controller, enabling the ROV to achieve accurate reference velocity tracking. Based on the theoretical idea of active disturbance rejection control, a kinematic equation-based ocean current observer was designed to estimate and compensate for large unknown currents to ensure accurate trajectory tracking performance under large currents. The simulation results proved that the double-loop sliding-mode control scheme with an ocean current observer always showed good tracking performance, demonstrating the excellent control performance and high robustness of the scheme. Compared with the high-complexity control schemes such as neural network-based PID control or fuzzy sliding mode control, it effectively improves the robustness to ocean current disturbances without increasing the computational effort excessively, and is more practical in ROV systems with limited computational power.

Highlights

With the explore and exploit process of marine resources, remote operation vehicles (ROVs) play an important role in many marine production activities
Among the mentioned control methods, sliding mode control (SMC) is increasingly used for the trajectory tracking control of ROVs under complex sea conditions because of its robustness to parameter changes and good suppression of external disturbances
To achieve the effective control of ROV systems, Rojsiraphisal and Vu [38] et al proposed the idea of combining the state observer and terminal sliding mode control, which greatly inspired the present scheme

Summary

Introduction

With the explore and exploit process of marine resources, remote operation vehicles (ROVs) play an important role in many marine production activities. Among the mentioned control methods, SMC is increasingly used for the trajectory tracking control of ROVs under complex sea conditions because of its robustness to parameter changes and good suppression of external disturbances. Xu et al [16] proposed a novel adaptive dynamical sliding mode control model, which combines backstepping control with traditional SMC This model enhances the robustness of ROVs under the conditions of systematical uncertainty and environmental disturbances. The scheme applies the multiple surfaces to approximate the unknown lumped perturbations simultaneously influencing a nonlinear system This demonstrates the great significance of state observers to improve the control performance of the system. To achieve the effective control of ROV systems, Rojsiraphisal and Vu [38] et al proposed the idea of combining the state observer and terminal sliding mode control, which greatly inspired the present scheme.

Ocean Currents

Ocean Current Observer

Simulation Results and Discussion

Controller Performance Comparison

Controller Robustness