Tech Briefs

Faults would be isolated, and systems would route power past damaged parts.

A research program has made progress toward the development of schemes for protection against faults in next-generation DC zonal shipboard electrical systems (DC SESs) and for configuration management in these systems to enable surviving parts of the systems to continue to distribute electric power to critical loads. Computational simulations of a representative prototype DC SES have shown that these schemes could afford protection at a system level (in contradistinction to a local level), thereby imparting, to the DC SES, an intended capability for self-healing.

Within a Zone, each of the non-critical loads would be connected to either the main or the alternate secondary DC bus, but not both. The critical loads would be connected to both buses via auctioneering diodes. During normal operation, the voltage on the main secondary bus would be somewhat higher than that on the alternate secondary bus, so the diodes would steer power from the main secondary bus to the critical loads. In the event of low voltage on the main secondary bus, the diodes would steer power from the alternate secondary bus to the critical loads

One basic principle of this research is that the DC SESs in question will incorporate voltage-source converters (VSCs) and other power electronic building blocks (PEBBs) so as to realize the potential advantages of DC power distribution over AC power distribution. Another basic principle is that many or perhaps all of the PEBBs could incorporate or be associated with computer-based electronic control subsystems that would cause the PEBBs to function as agents in an agent-based protection scheme. In the emerging discipline of agent-based design, which borrows heavily from the discipline of artificial intelligence, “agents” signifies, more specifically, agents that act autonomously in such a manner as to achieve a desired effect (e.g., zonal or system-wide protection).

The research program encompassed three parts: one focused on protection devices, one focused on the agent-based protection scheme, and one focused on the configuration-management scheme.

Protection Devices

In this part of the program, the focus was on the development of new protection devices that can rapidly limit fault (overload or short-circuit) currents and/or rapidly interrupt the distribution of power in zones containing faults. Two types of protection devices were found to be suitable:

VSCs could be used for limiting and interrupting fault currents. With suitable revisions of prior VSC designs, VSCs could be made to limit and interrupt fault currents within response times as short as a few microseconds.