Iterative Sliding Mode-Based Output Feedback Control for the Dynamic Positioning of Ships

Abstract

Abstract Because the velocities of a ship are unmeasured, a novel iterative sliding mode (ISM)-based output feedback control scheme is proposed for the dynamic positioning (DP) of a ship subjected to external environmental disturbances. First, the finite-time state observer is addressed, guaranteeing that estimated errors converge to a small neighborhood of zero in finite time with high precision. Furthermore, based on the outputs of the state observer, an ISM function is given. Then, the output feedback control scheme is designed for the DP of the ship with two remarkable features: (1) an integral item of the sign function exists in the control scheme, which inherently eliminates the chattering of the traditional sliding mode control (SMC), and (2) an integral term of the sliding mode is added to the control scheme, which is helpful in strengthening the transient response with lower overshooting. Finally, simulation studies and quantitative analysis are carried out to demonstrate the superior advantages of the proposed control scheme compared to the proportional-integral-derivative (PID) control scheme and the traditional SMC scheme.