Analytical approach for the optimal design of combined energy storage devices in ship power system

In the last years a great interest has been paid in the relevant literature to the benefits deriving from the use of direct current for ship power systems. This is in compliance with the most recent concept about all-electric-ship and smart electrical distribution for achieving better performances by exploiting as far as possible the potentiality of integrated power systems. In this context the storage devices play a crucial role in improving the reliability, the efficiency and the dynamic performances of the whole electric system. Moreover, compared to conventional ship propulsion plants, this approach has a significant impact on ship design (particularly when combined to azimuthing thruster or podded thrust units) as regards comfortable (noise and vibrations), flexibility (for general plan), consumption and environment protection. The variety of pulsed and intermittent loads also requires a proper choice of the storage devices and of the techniques for the optimal system design. Focusing on DC ship power systems, in this paper two different methodologies for the design of combined storage systems constituted by batteries and supercapacitors are proposed. Based on some typical loads, some relevant case studies are analyzed and discussed.