FUEL CELL SYSTEM AND CONTROL METHOD OF FUEL CELL SYSTEM

Provided is a fuel cell system including: a fuel cell; an anode gas supply device; a pressure sensor; a discharge valve; an estimation unit that estimates an anode gas concentration; and a control unit. The control unit performs first control of opening the discharge valve when a first valve opening condition is established in which the estimated anode gas concentration is equal to or lower than a first concentration, and closing the discharge valve when a first valve closing condition is established in which the estimated anode gas concentration is equal to or higher than a second concentration higher than the first concentration, and performs second control of closing the discharge valve when a deviation between the target pressure value and a value of the pressure sensor is continuously equal to or larger than a predetermined threshold for a predetermined period, and opening the discharge value when a second valve opening condition is established in which the estimated anode gas concentration is equal to or lower than a third concentration lower than the first concentration, or in which a value obtained by multiplying the estimated anode gas concentration by a predetermined coefficient so that the anode gas concentration is estimated to be high is equal to or lower than the first concentration.