Fuel cell system and control method thereof

A control method of a fuel cell system for generating electric power by supplying fuel gas to an anode of a fuel cell via a fuel gas supply flow path and supplying an oxygen-containing gas to a cathode of the fuel cell via an oxygen-containing gas supply flow path, the control method comprising:

• a freezing judgment step of judging whether a drain valve configured to discharge a discharge fluid from a liquid discharge port of a gas-liquid separator is frozen, the gas-liquid separator being configured to separate fuel exhaust gas discharged from the anode into a gas and a liquid, the discharge fluid including the liquid, wherein
• in the freezing judgment step, if it is judged that the drain valve is not frozen, the drain valve is kept in an open state and an unconsumed portion of the fuel gas contained in the discharge fluid is supplied along with the oxygen-containing gas to the cathode, and
• in the freezing judgment step, if it is judged that the drain valve is frozen, an opening and closing valve of a distribution flow path is kept in an open state, the distribution flow path being configured to distribute a discharge gas that is discharged from a gas discharge port of the gas-liquid separator or a mixed gas containing the discharge gas and the fuel gas supplied to the fuel gas supply flow path, to a downstream side of the drain valve in a connecting flow path configured to cause the liquid discharge port and the oxygen-containing gas supply flow path to be in communication with each other via the drain valve.