Fuel cell system and control method thereof

A fuel cell system, comprising:

• a fuel cell stack that is configured to have a cooling medium supply port and a cooling medium discharge port;
• a circulation flow path that is arranged to return a cooling medium which is discharged from the cooling medium discharge port, to the cooling medium supply port;
• a pump that is provided to drive the cooling medium in the circulation flow path and thereby circulate the cooling medium to inside of the fuel cell stack, the pump being configured to vary a circulation volume of the cooling medium;
• a supply-side temperature sensor that is configured to detect a supplied cooling medium temperature which is temperature of the cooling medium supplied to the cooling medium supply port;
• a discharge-side temperature sensor that is configured to detect a discharged cooling medium temperature which is temperature of the cooling medium discharged from the cooling medium discharge port;
• and
• a cold-start controller that is configured to control the circulation volume of the cooling medium by the pump at a cold start of the fuel cell stack, wherein
• the cold-start controller is configured to
• obtain a fuel cell internal temperature which is temperature inside of the fuel cell stack,
• selectively set the circulation volume of the cooling medium between a first circulation volume and a second circulation volume that is greater than the first circulation volume, based on a magnitude relationship between the fuel cell internal temperature and the discharged cooling medium temperature, and
• set the circulation volume of the cooling medium to a third circulation volume that is greater than the second circulation volume, when the supplied cooling medium temperature becomes equal to the discharged cooling medium temperature after setting the circulation volume.