Patent ID: 8159083

Claim:
Apparatus comprising: a main bus; an engine-driven electrical-energy source that is configured to supply electrical energy to the main bus; a secondary bus; a first electrical load electrically coupled to the secondary bus; a battery electrically coupled to the secondary bus; a first bi-directional direct-current-to-direct-current (“DC-DC”) converter that is configured to electrically couple the main bus to the battery and to the first electrical load; a second bi-directional DC-DC converter that is configured to electrically isolate the main bus from an ultracapacitor; at least one additional electrical load electrically coupled to the main bus other than through the first bi-directional DC-DC converter; wherein the first bi-directional DC-DC converter is configured to control current flow between the main bus and the secondary bus in response to a main-bus voltage level and a secondary-bus voltage level; and wherein the first bi-directional DC-DC converter is configured to electrically isolate the battery and the first load from the main bus upon the first load drawing a transient current that exceeds a threshold level.