Patent ID: 7547481

Claim:
A fuel-circulating fuel cell system comprising: a fuel cell that is supplied with fuel and an oxidizing agent, and generates electricity; a fuel-circulating passage that supplies fuel discharged from the fuel cell to the fuel cell again; a high-pressure hydrogen tank that supplies new fuel to the fuel cell; a fuel-forwarding device disposed in the fuel-circulating passage and provided with: a fuel pump that is powered from an outside source to circulate the fuel in the fuel-circulating passage at a predetermined circulation rate, and an ejector that forwards the new fuel from the high-pressure hydrogen tank to the fuel-circulating passage and circulates the fuel in the fuel-circulating passage at the predetermined circulation rate in combination with the fuel pump, wherein the fuel pump is disposed in the fuel-circulating passage at a location where the fuel discharged from the fuel cell flows away from the fuel cell and toward the ejector; means for monitoring a cell voltage of the fuel cell; means for determining an output instruction value based on the cell voltage of the fuel cell; means for transmitting the output instruction value to the fuel pump of the fuel-forwarding device to control the output of the fuel cell by controlling the fuel-forwarding device according to the output instruction value, thereby regulating a circulation rate of the fuel in the fuel-circulating passage; and means for increasing a rotation speed of the fuel pump based upon the output instruction value during operation of the fuel cell, wherein during operation the means for increasing comprises: means for rotating the fuel pump at a first rotation speed greater than zero when the cell voltage of the fuel cell falls within a predetermined range; and means for increasing the first rotation speed to a second rotation speed greater than the first rotation speed when the cell voltage of the fuel cell falls below the predetermined range.