Abstract
This article is concerned with the close formation problem of multiple underactuated surface vessels in the presence of model uncertainties, roll motion, and environmental disturbances. To effectively address these issues, a novel control scheme considering roll stabilization is designed by combing terminal hierarchical sliding mode control with Lyapunov direct method, which can quickly ensure a small formation error in a finite-time for vessels. Meanwhile, a new switching gain adaptation mechanism is utilized to reduce chattering and acquire faster adaptive rate without the excessive temporary tracking errors. Radial basis function neural network and finite-time observer are employed to deal with model uncertainties and disturbances, respectively. Furthermore, dynamic surface control technology is introduced to reduce the complexity of control law. Various simulations and comparison results are conducted to verify the effectiveness of theoretical results.
Highlights
Close formation control is receiving a considerable attention due to its important applications, such as cooperative exploration of ocean resources, underwater pipe-laying, and marine replenishment.[1]
Since the relative distance among vessels is small in close formation, the vessels are subjected to this kind of nonlinear complex disturbances from adjacent vessels and ocean simultaneously, resulting in serious roll motion, which will affect the navigation of vessels and the operation of instruments
Researchers have done a lot of scientific research on the formation control of underactuated surface vessels (USVs), we found that, only few research results have studied the close formation control of USVs and the effect of rolling for formation
Summary
Close formation control is receiving a considerable attention due to its important applications, such as cooperative exploration of ocean resources, underwater pipe-laying, and marine replenishment.[1]. THSMC includes two parts: hierarchical sliding mode control and terminal sliding mode control The former is coped with the underactuation of vessel, and the latter ensure the finite time convergence of the formation errors. The second first-order sliding surface is chosen as ðt s2 1⁄4 c5rbe 3 þ c6 redt where c5; c6; b3 are positive constants and 1 < b3 < 2. The switching gain employs a new adaptive law as follows h^_3 1⁄4 k 6swsignðS3ÞjjS3jj[1] À e3signðjjS3jj1Àe3ÞeðjjS3jj1Àe3Þ ð22Þ where k6sw; e3 are positive parameters and e3 represents sliding mode boundary threshold. O z zjV lðzÞ > 1⁄2D=ð1 À $ÞrV , and 0 < $ < 1
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