A novel fault-tolerant high-thrust inverter-controlled permanent magnet linear actuator as a direct-drive for shipboard loads

In today's large ships a wide use is made of hydrostatic transmission systems combined with traditional hydraulic machinery, such as piston-, rotary-vane- and screw-motors and pumps, to operate high-torque low-speed onboard actuators like rudders, stabilizing fins and bow thrusters. Such mechanical drives are very cumbersome and suffer from serious maintenance and reliability issues. In this paper, a novel all-electric direct-drive oil-free drive solution is proposed based on an inverter-fed permanent magnet linear synchronous motor (PMLSM). The PMLSM is coupled to shipboard rotary equipment through an innovative kinematic chain, consisting of a tiller and a prismatic-rotoidal joint, that performs force to torque conversion. The advantages of the PMLSM solution are presented in the paper in terms of compactness, robustness, reliability, efficiency and maintenance. Furthermore, the design optimization of a technology demonstrator which is presently under construction is addressed.