Solid oxide fuel cell system

A solid oxide fuel cell system for generating electricity by steam reforming fuel and reacting the resulting hydrogen with oxidant gas, comprising:

• a fuel cell module that includes a fuel cell stack;
• a fuel supply apparatus that supplies fuel to the fuel cell module;
• a water supply apparatus that supplies water for steam reforming to the fuel cell module;
• an oxidant gas supply apparatus that supplies oxidant gas to an oxidant gas electrode side of the fuel cell stack;
• a reformer disposed inside the fuel cell module that performs steam reforming of fuel supplied from the fuel supply apparatus using water supplied from the water supply apparatus and supplying the reformed fuel to a fuel electrode side of the fuel cell stack;
• and
• a controller programmed to control the fuel supply apparatus, water supply apparatus, and oxidant gas supply apparatus, as well as the extraction of power from the fuel cell module;
• wherein the controller includes a shutdown stop circuit that executes a shutdown stop in which the fuel supply and the electrical generation are stopped in a state whereby the fuel cell stack is at or above an oxidation suppression temperature;
• and
• wherein the shutdown stop circuit, by activating an oxidant gas supply apparatus, executes a temperature drop operation for discharging high temperature oxidant gas remaining on the oxidant gas electrode side within the fuel cell module after execution of a shutdown stop during a period in which the pressure on the fuel electrode side of the fuel cell stack is sufficiently higher than the pressure on the oxidant gas electrode side, and no reverse flow of oxidant gas to the fuel electrode side occurs.