Possible applications of plug-in hybrid electric ships

This paper presents the evolution of hybrid electric ships and the upcoming changes in hybrid electric propulsions by the addition of a battery based ESS. The inverter topology most suited for the expansion of the hybrid electric drive is the VSI inverter because this topology allows a DC/DC converter to control the power flow between the battery and the DC-bus of the propulsion motor. Different battery technologies are discussed by comparing the specifications of a 1 MWh reference battery. The impact of the addition of the batteries on the propulsion system is discussed. The battery allows the diesel generators to operate closer to their optimal efficiency by charging the battery when load is below optimal and by discharging the battery when load is above optimal. During anchoring, harbour docking, maneuvering and low speed cruising, the required power drops significantly and battery can take over from the diesel generators. The limited all-electric range allows the ship to shut off its engines some tens of km away from the harbour, improving local air quality. A large capacity battery can also improve safety by offering a few hours of all-electric low-speed cruising. In naval applications the all-electric range improves the stealth capabilities of the ship by reducing its acoustic and thermal signature. In the CODLAG configuration top speeds can be achieved with less prime movers by installing larger electric motors that are fed from both normal generators as well as the battery.