Fuel cell system and valve control method for fuel cell system

A valve control method for a fuel cell system, the fuel cell system comprising:

• a fuel cell stack configured to generate electric power using an anode gas in an anode flow field and a cathode gas in a cathode flow field;
• an anode supply flow path configured to supply the anode gas to the anode flow field;
• a cathode supply flow path configured to supply the cathode gas to the cathode flow field;
• a circulation flow path configured to return an exhaust fluid discharged from the anode flow field to the anode supply flow path;
• a connection flow path configured to supply the exhaust fluid discharged from the anode flow field to the cathode supply flow path;
• a valve configured to open and close the connection flow path;
• and
• a computer configured to control opening and closing of the valve,
• the valve control method comprising
• causing the computer to:
• store a first threshold amount of nitrogen on a basis of which whether to perform control for reducing nitrogen in the anode flow field is determined and a second threshold pressure on a basis of which opening and closing of the valve is determined;
• measure or estimate an amount of nitrogen in the anode flow field;
• perform a first comparison by comparing the first threshold amount with the amount of nitrogen;
• perform a second comparison by comparing the second threshold pressure with a differential pressure calculated by subtracting a cathode pressure value indicating a pressure inside the cathode flow field from an anode pressure value indicating a pressure inside the anode flow field in a case where the amount of nitrogen in the anode flow field is greater than the first threshold amount in the first comparison;
• and
• control opening and closing of the valve based on a result of the first comparison and a result of the second comparison, and
• the computer opens the valve in a case where the differential pressure is greater than the second threshold pressure in the second comparison, and closes the valve in a case where the differential pressure is lower than the second threshold pressure.