Patent ID: 7931994

Claim:
A fuel cell system comprising: a fuel cell configured to generate power from fuel gas supplied thereto; a supply system configured to supply fuel gas to the fuel cell; a recirculation system configured to recirculate unused fuel gas from the fuel cell, wherein fuel gas in the recirculation system contains nitrogen; a purge valve configured to purge nitrogen contained in the fuel gas in the recirculation system, wherein the purge valve is configured such that a valve opening degree of the purge valve is controlled to be reduced or increased; and a controller configured to adjust the valve opening degree of the purge valve such that a nitrogen concentration of the fuel gas in the recirculation system is controlled to be maintained at a target nitrogen concentration, wherein the controller is configured to: adjust the valve opening degree of the purge valve to maintain a flow rate of fuel in a fuel gas passing through the purge valve at a threshold set in accordance with operation conditions of the fuel cell system and the valve opening degree of the purge valve, by reducing the valve opening degree of the purge valve if the flow rate of fuel in the fuel gas passing through the purge valve is more than the threshold, and increasing the valve opening degree of the purge valve if the flow rate of the fuel gas passing through the purge valve is less than the threshold.