Motion control of marine electrical drives: Technical assessment and perspectives

Several different models for the propulsive shaft system have been proposed in literature. In this paper, the so called thruster level model is considered. Basically the system is composed of a propulsion motor, a transmission device (a shaft) and a propeller. In all-electric ships, propulsion is realized utilizing electrical drives. Time varying propeller loading induced by waves, hydrodynamics effects like cavitation, ventilation, variations in submerged level of the propeller interacts with the multi-mass system composed by the electrical motor, the shaft and the propeller. It is therefore important to investigate the resonance frequency of such system.