6. Conclusion
Power electronics plays a key role in MVDC power systems. Technology is nowadays going to become mature enough to make MVDC power systems for AES a realistic alternative to MVAC power systems. Realization costs are still higher than MVAC power systems, but the expected benefits are such to attract the interest of shipbuilders, who want to be ready to provide their ships with MVDC power system when the technology will be mature enough and the scale production will make it affordable.
In this paper a survey has been provided of the most promising technologies for power electronics equipment to be employed in shipboard MVDC power systems. The power electronics equipment has been classified according to the IEEE Std 1709™-2010 into three subsystems, namely power sources, load centers and distribution network.
Regarding power sources, power converters for power generation, energy storage and shore power interface are presented. In particular, different kinds of DC generation systems have been described also making reference to some built and tested full-scale prototypes specifically conceived for MVDC military vessels. It has been highlighted how the choice of the converter is closely connected to the adopted electric generator technology.
Regarding load centers, power converters for propulsion, ship services, dedicated high power loads and pulse loads are presented. Attention is particularly focused on step-down SSTs which interconnect ship services to the MVDC bus. A detailed classification has been presented for the large number of step-down DC/DC converters found in the literature highlighting the features which particularly fit to serve as SSTs. Finally, combining three existing topologies, a new SST architecture has been proposed exhibiting the following benefits: (1) fault tolerance, thanks to the multi-phase and modular structure, (2) design and realization advantages, thanks to the energy flow sharing between multiple converter legs and modules, (3) voltage subdivision, thanks to the NPC legs and modular structure, (4) limited losses, thanks to the resonant AC circuit.
