MVDC supply technologies for marine electrical distribution systems

The increase in the popularity of the medium voltage dc (MVDC) electrical distribution, as a possible evolution of the medium voltage ac (MVAC) electrical distribution for the ship onboard power systems, arises a need for a comparative evaluation and demonstration of feasible technologies for the MVDC supplies. For designing the MVDC supplies in the range from 5-35 kV, different available technologies can be considered for the designs and have a direct influence on the overall system performance. In this paper, different technologies for prime movers, electrical generators and rectifiers are discussed in terms of feasibility for the MVDC supplies. Different supply configurations can be envisioned from these based on the commercial availability, quality of supply, efficiency, dynamic performance and volume. Multi-phase multipulse supply configurations are identified and proposed for the marine MVDC systems. Combination of multi-phase generators and multi-pulse rectifiers offer reliable, simple and fault tolerant solution with acceptable dynamics. To explore and highlight these benefits, a six-pulse rectifier sub-module is designed and analysed in two arrangements for multi-pulse configurations, namely parallel and series. It has been shown that with appropriate selection of semiconductor devices, coupled with properly selected fast fuses, excellent fault current (thermal) withstand capabilities can be achieved.