Considerations when diode auctioneering multiple DC buses in a non-isolated DC distribution system

Power continuity is maintained to critical loads in shipboard DC distribution systems by diode auctioneering the outputs of DC/DC power converters fed from separate main DC buses. In order to minimize the size/weight of power conversion non-isolated three-level buck converters are used to convert voltage from a higher main bus voltage level (typically 1000VDC) to lower ship load DC voltages (i.e. 650VDC, 850VDC, etc.). Two buses of the same voltage level are paralleled without issue. However if more than one buck converter or group of paralleled buck converters are used to create more than one voltage feed that is paralleled with similar converters connected to the opposite main bus through auctioneering diodes then paths for circulating currents may be created during the unsynchronized commutation states of opposite bus power semiconductors. In addition, the auctioneering of two or more buses presents particular challenges to maintaining power continuity throughout the ship when more than one ground fault is applied. This paper documents the lessons learned based on simulation and tests on a 3MW system and identifies measures that can be taken to ensure robust operation during normal modes of operation and survive multiple ground fault scenarios.