A fuel cell system determines each of a battery charging current error, a battery voltage error, and a stack current error. The fuel cell system regulates current through a series pass element in response to a greater of the determined errors, operating in three modes: battery voltage limiting mode,...http://www.google.co.uk/patents/US6573682?utm_source=gb-gplus-sharePatent US6573682 - Fuel cell system multiple stage voltage control method and apparatus
