Solid oxide fuel cell system

A solid oxide fuel cell system comprising:

• a fuel cell stack that generates electric power through a reaction between a fuel gas and an oxidizing gas;
• a combustor in which anode and cathode off-gases discharged from the fuel cell stack are burned by diffusion combustion;
• a temperature sensor that detects temperature of the anode off-gas flowing into the combustor;
• and
• a controller,
• wherein, when the controller determines that the system is in at least one of the following states (i) or (ii), the controller is programmed to instruct the system to perform a power-generation control action for preventing failed reactions in the diffusion combustion:
• (i) the temperature of the anode off-gas, detected by the temperature sensor while the solid fuel cell system is in power-generating operation, is below a first predetermined temperature for a predetermined continuous period of time;
• and
• (ii) the temperature of the anode off-gas, detected by the temperature sensor while the solid fuel cell system is in power-generating operation, decreases by not less than a predetermined second temperature range during a predetermined period of time, and
• wherein the controller is further programmed to instruct the system to stop the power-generation control action and switch to open circuit voltage (OCV) operation, in which the fuel cell stack does not generate power but remains fed with the fuel and oxidizing gases, when the controller determines, during the power-generation control action, that the temperature of the anode off-gas is below a third predetermined temperature, set lower than the first predetermined temperature, for a predetermined continuous period of time.