Under-actuated surface vessels (USVs) are universally used. With the characteristics of multi-variable, nonlinear and under-actuation, control problems of USVs remain challenging, especially the full-state stabilization of the USVs is theoretically the most difficult.
Since digital devices are used to control the USVs, the new control value is computed periodically at each sampling time, which may result in unnecessary high workloads and utilization of resources.
Moreover, the mechanism of periodic implementations requires renewing the actuator state at every sampling instant, leading to unnecessary energy consumptions and even actuator attritions.
Recently, researchers from the Institute of Acoustics of the Chinese Academy of Sciences (IACAS) proposed a global event-triggered stabilization design method for USV, which reduced communication time and the actuator burden while providing stable and accurate control performance.
Based on an inner-outer loop structure with Lyapunov control design technique, researchers separated the USV dynamics into two subsystems to facilitate the design and stability analysis. They constructed a time-varying variable to design the desired velocities used as virtual control inputs to stabilize the under-actuated outer loop subsystem.
For the fully-actuated inner loop subsystem, they designed the actual control force and moment inputs using a switching threshold event-triggering mechanism to drive the actual velocities to the desired ones, thereby stabilizing the inner loop subsystem and the closed-loop system.
The proposed event-triggered controller guaranteed global asymptotical convergence of the stabilization error by choosing proper control parameters.
Numerical simulation results indicated that the proposed control scheme had features of higher control accuracy, lower energy consumption and less communication time, compared with the traditional control methods.
The research, published in Ocean Engineering, was supported by the National Natural Science Foundation of China.
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