A converter to interface ultra-capacitor energy storage to a fuel cell system

This paper describes a DC-DC power converter for charging and discharging an ultra-capacitor module within a small, sustainable energy system. The energy source in the system is a fuel cell, and a bidirectional grid-connected inverter supplies local AC loads, exports excess energy to the grid, and can import energy if required to charge the capacitors. The capacitor charger provides an interface between the near-constant voltage of a common DC bus and the widely varying ultra-capacitor voltage. The fuel cell system is normally operated with a battery bank at it´s output. Therefore, the particular feature of the converter is that it provides closed-loop voltage control of the common DC bus. in order to emulate simplified voltage-current terminal characteristics of batteries.