Patent ID: 8232013

Claim:
A fuel cell system comprising: a fuel cell configured to generate power by electrochemical reaction between a fuel gas supplied to a fuel electrode and an oxidizer gas supplied to an oxidizer electrode; a fuel gas supply channel through which the fuel gas is supplied to the fuel electrode; a circulation channel through which a gas discharged from the fuel electrode of the fuel cell is fed to the fuel gas supply channel; a circulator unit configured to circulate the fuel gas, the circulator unit being provided in the circulation channel; a discharge channel through which a gas flowing in the circulation channel is discharged; a discharge amount-adjusting unit configured to adjust an amount of an impurity to be discharged through the discharge channel; a mode switching unit programmed to switch a driving mode between a normal power generation mode in which power required by the system is supplied through power generation in the fuel cell and an idle mode in which power generation in the fuel cell is stopped and power required by the system is supplied from a power storing unit; a mode switching probability unit programmed to determine a switching probability based on a switching condition; a setting unit programmed to variably set a target control value of an impurity content in at least one of the circulation channel and the fuel electrode based on the switching probability; and a controller programmed to control the discharge amount-adjusting unit based on the target control value.