Solid oxide fuel cell system and method for controlling same

1. A solid oxide fuel cell system comprising:

a fuel cell stack including a fuel electrode and an oxidant electrode;

a reformer configured to reform a fuel gas into a reformed gas and to supply the reformed gas to the fuel electrode of the fuel cell stack;

a combustion unit provided to start the system and configured to supply a combustion gas to the oxidant electrode of the fuel cell stack, the combustion gas containing an inert gas as a component;

a combustion gas flow passage configured to supply part of the combustion gas discharged from the combustion unit to the fuel electrode of the fuel cell stack;

a combustion gas container disposed in the middle of the combustion gas flow passage and configured to contain the combustion gas; and

a control unit programmed to:

supply part of the combustion gas discharged from the combustion unit to the oxidant electrode of the fuel cell stack and cause the combustion gas container to contain the other part of the combustion gas discharged from the combustion unit at the time of starting the system, and

control in such a way as to fill the combustion gas contained in the combustion gas container into the fuel electrode of the fuel cell stack at the time of stopping the system.

2. A solid oxide fuel cell system comprising:

a fuel cell stack including a fuel electrode and an oxidant electrode;

a combustion unit provided to start the system and configured to supply a combustion gas to the fuel electrode of the fuel cell stack, the combustion gas containing an inert gas as a component;

a start flow passage configured to supply the combustion gas discharged from the combustion unit to the fuel electrode of the fuel cell stack at the time of starting the system;

a stop flow passage configured to supply the combustion gas discharged from the combustion unit to the fuel electrode of the fuel cell stack at the time of stopping the system;

a heat exchanger disposed in the middle of the stop flow passage; and

a control unit programmed to select the start flow passage at the time of starting the system and to select the stop flow passage and operate the combustion unit to fill the combustion gas into the fuel electrode of the fuel cell stack at the time of stopping the system;

wherein based on a determination by the control unit that the combustion gas is filled into the fuel electrode of the fuel cell stack at the time of stopping the system, the control unit closes an inlet and an outlet of the fuel electrode of the fuel cell stack.

3. The solid oxide fuel cell system according to claim 1 , further comprising:

a circulation gas flow passage configured to circulate a fuel electrode exhaust gas discharged from the fuel electrode of the fuel cell stack to the reformer; and

a heating gas flow passage configured to mix part of the fuel electrode exhaust gas branched off from the circulation gas flow passage with an oxidant electrode exhaust gas discharged from the oxidant electrode of the fuel cell stack, and to supply the mixture as a heating gas for the reformer.

4. A method for controlling a solid oxide fuel cell system, the system being provided with a fuel cell stack having a fuel electrode and an oxidant electrode, a combustion unit provided to start the system, and a control unit to control the system, the method comprising:

supplying part of a combustion gas discharged from the combustion unit into the oxidant electrode of the fuel cell stack and causing a combustion gas container to contain the other part of the combustion gas discharged from the combustion unit at the time of starting the system, the combustion gas containing an inert gas as a component; and

filling the combustion gas contained in the combustion gas container into the fuel electrode of the fuel cell stack at a time of stopping the system.