FUEL CELL SYSTEM AND OPERATION METHOD THEREOF

1 . A fuel cell system comprising:

a fuel cell including an anode and a cathode;

a fuel gas supply unit configured to supply a fuel gas to the anode, the fuel gas containing at least hydrogen;

an oxidizing gas supply unit configured to supply an oxidizing gas to the cathode, the oxidizing gas containing at least oxygen;

an anode inert gas supply unit configured to supply an inert gas to the anode to replace the fuel gas, at least partially, with the inert gas;

a voltage detector configured to detect a cell voltage of the fuel cell;

a cooling unit configured to cool the fuel cell;

a temperature detector configured to detect a temperature of the fuel cell; and

a controller configured to control operations of the fuel cell, the fuel gas supply unit, the oxidizing gas supply unit, and the anode inert gas supply unit, wherein

the controller:

performs a stop operation of stopping electric power generation by the fuel cell;

then performs an activity recovery operation of stopping the supply of the fuel gas by the fuel gas supply unit to the anode, causing the anode inert gas supply unit to supply the inert gas to the anode, and causing the oxidizing gas supply unit to supply the oxidizing gas to the cathode;

performs control such that the fuel gas supply unit resumes supplying the fuel gas to the anode to resume the electric power generation by the fuel cell after the cell voltage of the fuel cell which is detected by the voltage detector has decreased to a first voltage or lower; and

performs at least one of

control to decrease the temperature of the fuel cell to a first temperature or lower before the activity recovery operation, and

control to decrease the temperature of the fuel cell to a second temperature or lower and cause the fuel cell to perform the electric power generation at a start-up operation of the fuel cell.

2 . The fuel cell system according to claim 1 , wherein

the controller:

performs the stop operation such that the stop operation includes stopping the electric power generation by the fuel cell, stopping the supply of the oxidizing gas by the oxidizing gas supply unit to the cathode, and stopping the supply of the fuel gas by the fuel gas supply unit to the anode; and

performs control to perform the activity recovery operation after the cell voltage of the fuel cell which is detected by the voltage detector has decreased to a second voltage or lower.

3 . The fuel cell system according to claim 1 ,

wherein the controller:

performs the stop operation such that the stop operation includes stopping the electric power generation by the fuel cell and controlling the cooling unit to cool the fuel cell; and

performs control to perform the activity recovery operation after the temperature of the fuel cell which is detected by the temperature detector has decreased to the first temperature or lower.

4 . The fuel cell system according to claim 3 ,

wherein the controller:

performs the stop operation such that the stop operation includes controlling the cooling unit such that the temperature of the fuel cell which is detected by the temperature detector becomes the first temperature or lower, causing the fuel cell to perform the electric power generation for a second period, and then stopping the electric power generation by the fuel cell; and

then performs control to perform the activity recovery operation.

5 . The fuel cell system according to claim 1 ,

wherein

at the start-up operation of the fuel cell, the controller controls the cooling unit such that the temperature of the fuel cell becomes the second temperature or lower, and performs control such that the fuel cell performs the electric power generation for a third period.

6 . The fuel cell system according to claim 1 , wherein the controller performs control to perform the activity recovery operation such that the activity recovery operation includes stopping the supply of the fuel gas by the fuel gas supply unit to the anode, causing the anode inert gas supply unit to supply the inert gas to the anode, and then causing the oxidizing gas supply unit to supply the oxidizing gas to the cathode.

7 . The fuel cell system according to claim 1 , wherein

each time a first period has elapsed, the controller performs the stop operation, then performs the activity recovery operation, and thereafter performs control to resume the electric power generation by the fuel cell.

8 . The fuel cell system according to claim 7 , wherein the first period is controlled by the controller and is a period over which a power generation time cumulative value, which indicates a cumulated power generation time of the fuel cell, reaches a predetermined cumulative power generation time.

9 . The fuel cell system according to claim 1 , wherein

the anode inert gas supply unit includes a desulfurizer configured to desulfurize a raw material gas, and

the inert gas is the raw material gas desulfurized by the desulfurizer.

10 . The fuel cell system according to claim 1 , wherein the anode inert gas supply unit is configured to supply the inert gas to the anode via the fuel gas supply unit.

11 . A method of operating a fuel cell system including a fuel cell including an anode and a cathode, the fuel cell system causing the fuel cell to perform electric power generation by supplying a fuel gas containing at least hydrogen to the anode and supplying an oxidizing gas containing at least oxygen to the cathode, the method comprising:

a stopping step of stopping the electric power generation by the fuel cell;

an activity recovering step of then stopping the supplying of the fuel gas to the anode, supplying the inert gas to the anode, and supplying the oxidizing gas containing at least oxygen to the cathode; and

a resuming step of resuming, after a cell voltage of the fuel cell has decreased to a first voltage or lower, the supplying of the fuel gas to the anode to resume the electric power generation by the fuel cell,

the method further comprising at least one of:

a step of decreasing a temperature of the fuel cell to a first temperature or lower before the activity recovering step; and

a step of decreasing the temperature of the fuel cell to a second temperature or lower and causing the fuel cell to perform the electric power generation at a start-up operation of the fuel cell.

12 . The method of operating the fuel cell system according to claim 11 , wherein

the stopping step includes stopping the electric power generation by the fuel cell, stopping the supplying of the oxidizing gas to the cathode, and stopping the supplying of the fuel gas to the anode, and

after the stopping step, when the cell voltage of the fuel cell has decreased to a second voltage or lower, the activity recovering step is performed.

13 . The method of operating the fuel cell system according to claim 11 , wherein

the stopping step includes stopping the electric power generation by the fuel cell and cooling the fuel cell, and

the activity recovering step is performed after the temperature of the fuel cell has decreased to the first temperature or lower.

14 . The method of operating the fuel cell system according to claim 13 , wherein

the stopping step includes:

cooling the fuel cell such that the temperature of the fuel cell becomes the first temperature or lower; and

causing the fuel cell to perform the electric power generation for the second period, and then stopping the electric power generation by the fuel cell, and

the activity recovering step is performed after the stopping step.

15 . The method of operating the fuel cell system according to claim 11 , comprising

at the start-up operation of the fuel cell, cooling the fuel cell such that the temperature of the fuel cell becomes the second temperature or lower and causing the fuel cell to perform the electric power generation for a third period.

16 . The method of operating the fuel cell system according to claim 11 , wherein

the activity recovering step includes stopping the supplying of the fuel gas by the fuel gas supply unit to the anode, causing the anode inert gas supply unit to supply the inert gas to the anode, and then causing the oxidizing gas supply unit to supply the oxidizing gas to the cathode.

17 . The method of operating the fuel cell system according to claim 11 , wherein

each time a first period has elapsed, the stopping step is performed, then the activity recovering step is performed, and thereafter the resuming step is performed.

18 . The method of operating the fuel cell system according to claim 17 , wherein the first period is a period over which a power generation time cumulative value, which indicates a cumulated power generation time of the fuel cell, reaches a predetermined cumulative power generation time.