Robust Tension Control of the Anchor Chain of the Ship Windlass under Sea Wind

Constant tension control of anchor chains is important for safety of moored ships. The core driving component of an anchor windlass system is an induction motor which is a multi-variables, coupled nonlinear system, and is difficult to control. To surmount this problem, a control scheme based on the inverse system method is introduced to linearize an induction motor into a decoupled linear system, and linear controllers are then designed to complete the control task. In addition, theoretical analysis based on the Lyapnov method is carried out to investigate the influence of the time-varying rotor resistance to the control scheme suggested. Both theoretical analysis and numerical simulations show this control scheme is able to keep anchor chains at desired tension under sea wind at a time-varying rotor resistance.