Fuel cell system and control method thereof

1 . A fuel cell system comprising:

a fuel cell stack comprising an anode and a cathode;

a nitrogen tank configured to store nitrogen drained from the cathode, and to supply the stored nitrogen to the anode; and

a controller configured to control the storing of the nitrogen and the supplying of the nitrogen, based on one or more of a pressure and a filling amount of the nitrogen tank,

wherein the controller is configured to store the nitrogen into the nitrogen tank based on a preset condition being satisfied,

wherein the preset condition is varied corresponding to operating state of the fuel cell stack,

wherein the operating state of the fuel cell stack is a lower-output operating state and a higher-output operating state.

2 . The fuel cell system of claim 1 , wherein the nitrogen tank comprises an input valve and an output valve, and

wherein the controller is further configured to control opening or closing of the input valve and the output valve to control the storing and the supplying of the nitrogen.

3 . The fuel cell system of claim 2 , wherein the controller is further configured to open the input valve and to close the output valve, in response to a first condition being satisfied during the lower-output operation of the fuel cell stack, and to close the input valve and the output valve, in response to the first condition not being satisfied.

4 . The fuel cell system of claim 3 , wherein the first condition is at least one of the filling amount of the nitrogen tank being less than a first value, or the pressure of the nitrogen tank being equal to or less than a pressure of the cathode.

5 . The fuel cell system of claim 4 , wherein the controller is further configured to:

open the input valve and close the output valve, in response to a second condition being satisfied during the higher-output operating state of the fuel cell stack; and

close the input valve and the output valve, in response to the second condition not being satisfied.

6 . The fuel cell system of claim 5 , wherein the second condition is at least one of the filling amount of the nitrogen tank being less than a second value, or the pressure of the nitrogen tank being equal to or less than the pressure of the cathode.

7 . The fuel cell system of claim 2 , wherein the controller is further configured to:

open the input valve and close the output valve, in response to the pressure of the nitrogen tank being less than a third value after an operation of the fuel cell stack is terminated; and

close the input valve and the output valve, in response to the pressure of the nitrogen tank being equal to or greater than the third value.

8 . The fuel cell system of claim 7 , wherein the controller is further configured to:

open the output valve, in response to a first time elapsing after the operation of the fuel cell stack is terminated and after the input valve is closed.

9 . The fuel cell system of claim 8 , wherein the controller is further configured to control to close the output valve and to enter into a power saving mode, in response to a pressure drop of the nitrogen tank being stopped.

10 . The fuel cell system of claim 9 , wherein the controller is further configured to

open the output valve, in response to a second time being elapsed without the operation of the fuel cell stack, after entering into the power saving mode.

11 . A processor-implemented method of controlling a fuel cell system including a fuel cell stack comprising an anode and a cathode, the method comprising:

storing nitrogen drained from the cathode in a nitrogen tank, and supplying the stored nitrogen to the anode;

determining pressure and a filling amount of the nitrogen tank; and

controlling the storing and the supplying of the nitrogen, based on one or more of the pressure and the filling amount of the nitrogen tank,

wherein the controlling the storing the nitrogen includes storing the nitrogen into the nitrogen tank based on a preset condition being satisfied,

wherein the preset condition is varied corresponding to operating state of the fuel cell stack,

wherein the operating state of the fuel cell stack is a lower-output operating state and a higher-output operating state.

12 . The control method of claim 11 , wherein the nitrogen tank comprises an input valve and an output valve, and

wherein the controlling of the storing and the supplying of the nitrogen comprises controlling opening and closing of the input valve and the output valve to control the storing and the supplying of the nitrogen.