Fixed-time dynamic threshold event-triggered anti-windup collaborative control for multi-tug towing of unactuated offshore floating platform
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This paper proposes a fixed-time event-triggered anti-windup collaborative controller for a towing system consisting of an unactuated offshore platform and multiple tugs. Firstly, a fixed-time virtual controller is proposed to acquire required towing force for the platform to track expected trajectory. Subsequently, the required towing force is allocated as desired towline tensions by quadratic programming algorithm, and corresponding desired length of each towline is calculated through towline catenary model. Based on desired towline tensions and lengths, a fixed-time collaborative controller is constructed for tugs with following key components: the input saturation of tugs is approximated by a Gaussian error function; a fixed-time extended state observer is employed to rapidly estimate compound disturbances including saturation approximation errors; a novel dynamic threshold event-triggered mechanism is designed to decrease the control input update frequency while maintaining the convergence performance of entire control system. Finally, simulation results demonstrate the effectiveness of proposed control method.
Abstract
This paper proposes a fixed-time event-triggered anti-windup collaborative controller for a towing system consisting of an unactuated offshore platform and multiple tugs. Firstly, a fixed-time virtual controller is proposed to acquire required towing force for the platform to track expected trajectory. Subsequently, the required towing force is allocated as desired towline tensions by quadratic programming algorithm, and corresponding desired length of each towline is calculated through towline catenary model. Based on desired towline tensions and lengths, a fixed-time collaborative controller is constructed for tugs with following key components: the input saturation of tugs is approximated by a Gaussian error function; a fixed-time extended state observer is employed to rapidly estimate compound disturbances including saturation approximation errors; a novel dynamic threshold event-triggered mechanism is designed to decrease the control input update frequency while maintaining the convergence performance of entire control system. Finally, simulation results demonstrate the effectiveness of proposed control method.