Transient short circuit analysis in DC on-board distribution systems fed by synchronous generators through 6-pulse diode rectifiers

Recent advancements in power electronics are making it feasible to build high power DC distribution systems. Their adoption is expected to bring new solutions in terms of Power Quality and integration of energy storage systems and electronic drives on board. The increasing interest in high-power onboard applications, such as in ships or railway transportation, led to the rise in voltage levels, which in turn caused an increase in short-circuit currents; therefore, a careful assessment has to be done to design system protections. Moreover, in onboard power systems, a continuous connection to the grid is not feasible (except in rare cases, such as trains), so power generation is usually made using rectified synchronous generators. The absence of a constant-voltage infinite-power bus complicates short-circuit currents calculation, making necessary to consider generators internal dynamics during short circuit transients. In this paper two different approaches to evaluate DC short circuit currents are proposed. A dual validation is done, through a first comparison with IEC 61660-1 Standard and then using time-domain simulation of a circuit model, under the constant supply voltage hypothesis. Then, the synchronous generator supply is considered, and its internal dynamics impact on DC short-circuit currents is assessed. Proper case studies are presented, to show the differences between the proposed approaches.