Direct Drive Propeller System Modelling and Active Protection

The advancements in power electronics, magnetic materials, and manufacturing technologies have resulted in the revolutionary innovation of direct drive propulsion systems in marine industry. The direct propulsion systems have been characterised with instantaneous torque control, which makes them superb in manoeuvrability and dynamic performance, and have been deployed in extreme applications like ice breakers and arctic tankers. The operations at these extreme sea conditions can affect the healthiness of the bearings in the direct drive systems, and operational limitations have been specified by the shipping industry to ensure proper safety of the ship and the propulsion unit. In addition to these operation limitations, it will be beneficial to have an active protection scheme to improve the reliability. In this paper, an active protection scheme, based on speed difference between motor and propeller, is proposed for the direct drive propulsion system, and controller design is explained. The advanced control can reduce shaft over torque and dynamic mismatch considerably. The control algorithm is tested under both simulations as well as in experimental setup under foreign body impact condition.