Fuel cell system including control of rotation speed of a gas pump

A fuel cell system, comprising:

• a fuel cell;
• a circulation passage that is configured to circulate an exhaust gas discharged from the fuel cell, to a supply port of a fuel gas in the fuel cell;
• a hydrogen gas pump that is provided in the circulation passage and is configured to have a rotating body and circulate the exhaust gas discharged from the fuel cell to the fuel cell by rotation of the rotating body;
• a hydrogen gas pump controller that is programmed to control rotation speed of the rotating body of the hydrogen gas pump;
• a demand acquirer that is configured to obtain a power generation demand for the fuel cell;
• and
• a temperature acquirer that is configured to obtain temperature of the fuel cell at which water introduced through the circulation passage into the hydrogen gas pump is generated, at a start-up time of the fuel cell, wherein
• the hydrogen gas pump controller is programmed to:
• obtain a first rotation speed in accordance with the obtained power generation demand when the fuel cell starts power generation,
• control a rotation speed of the rotating body of the hydrogen gas pump to the first rotation speed corresponding to the power generation demand, when the temperature of the fuel cell when the fuel cell starts power generation is higher than a predetermined reference temperature that is not higher than zero degree Celsius, and
• control, only once during each power generation by the fuel cell, the rotation speed of the rotating body of the hydrogen gas pump to a second rotation speed that is greater than zero and is lower than the first rotation speed, when the temperature of the fuel cell when the fuel cell starts power generation is not higher than the reference temperature, wherein
• the reference temperature is a temperature that allows the water to be introduced in a supercooled state into the hydrogen gas pump, and
• the second rotation speed that is a rotation speed in a low rotation speed range that allows the water in the supercooled state introduced into the hydrogen gas pump to be extended between the rotating body and a rotating body-surrounding housing wall.