Method for controlling fuel cell system

A method for controlling a fuel cell system having a fuel cell to generate power according to an electrochemical reaction of an oxide gas supplied to a cathode side with a fuel gas supplied to an anode side, an oxide-gas supply apparatus to supply the oxide gas to the fuel cell, a fuel-gas supply apparatus to supply the fuel gas to the fuel cell, and a scavenging apparatus to execute an in-soak-mode scavenging gas replacing process of scavenging the anode side with a scavenging gas at a time of soaking after power generation of the fuel cell is stopped, the fuel cell system being configured to execute an upon-startup fuel gas replacing process of supplying the fuel gas to the anode side to discharge an anode-off gas when the fuel cell is started, the method comprising:

• determining whether an in-stop-mode power generating process is executed since an operation stop instruction to stop an operation of the fuel cell is detected until the fuel cell system is stopped, the in-stop-mode power generating process including stopping supply of the fuel gas, stopping supply of the oxide gas to the fuel cell to generate power from the oxide-gas supply apparatus after the stopping of supply of the fuel gas, and stopping power generation of the fuel cell after the stopping of supply of the oxide gas;
• setting, as a first amount, an amount of the fuel gas to be used in case of executing the upon-startup fuel gas replacing process before an in-soak-mode scavenging gas replacing process is executed by the scavenging apparatus when it is determined that the in-stop-mode power generating process is executed, if the operation stop instruction to stop the operation of the fuel cell is detected;
• and
• setting, as a second amount, an amount of the fuel gas to be used in case of executing the upon-startup fuel gas replacing process before the in-soak-mode scavenging gas replacing process is executed by the scavenging apparatus when it is determined that the in-stop-mode power generating process is not executed, if the operation stop instruction to stop the operation of the fuel cell is detected, the first amount being larger than the second amount;
• and
• determining whether or not an elapsed time since the stopping of the power generation of the fuel cell until an operation start instruction to start the fuel cell system is detected is shorter than a specified time, if the operation start instruction to start the fuel cell system is detected after the power generation of the fuel cell is stopped, wherein the setting of the first amount includes setting the first amount if it is determined that the elapsed time is shorter than the specified time, and
• the setting of the second amount includes setting the second amount if it is determined that the elapsed time is shorter than the specified time;
• wherein the specified time is defined as a period of time from a point of time when operation of the fuel cell system is stopped after the in-stop-mode power generating process is executed to a point of time when hydrogen concentration drops down to a predetermined threshold concentration.