Fuel cell system and method for controlling purge thereof

1. A fuel cell system comprising:

a purge valve configured to discharge hydrogen on a hydrogen supply line that passes a fuel cell stack;

an operation state monitoring device configured to monitor an operation state of the fuel cell stack; and

a controller configured to determine a purge frequency based on the operation state, and to control the purge valve based on the determined purge frequency,

wherein the controller is further configured to:

determine a first purge frequency, at which the power generation efficiency of the fuel cell stack reaches a maximum efficiency point,

wherein the controller is further configured to:

search for a second purge frequency, at which a changed maximum efficiency point is reached, while the purge frequency is adjusted in unit of a specific time period, when the maximum efficiency point for the power generation efficiency of the fuel cell stack is changed to the changed maximum efficiency point during an operation thereof.

2. The fuel cell system of claim 1 , wherein the operation state monitoring device is configured to:

monitor at least one of a current, a voltage, a power generation efficiency, or a hydrogen supply amount of the fuel cell stack, or a combination thereof.

3. The fuel cell system of claim 2 , wherein the operation state monitoring device is further configured to:

monitor the operation state based on an average value for the operation state.

4. The fuel cell system of claim 1 , wherein the controller is further configured to:

increase or decrease the purge frequency in unit of the specific time period, based on a change in the power generation efficiency and a change in a voltage of the fuel cell stack.

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

increase the purge frequency when the power generation efficiency and the voltage of the fuel cell stack become higher than a power generation efficiency and a voltage at a previous time point.

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

decrease the purge frequency when the voltage of the fuel cell stack becomes lower than that at a previous time point while the power generation efficiency of the fuel cell stack becomes higher than that at the previous time point.

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

increase the purge frequency when the power generation efficiency and the voltage of the fuel cell stack become lower than a power generation efficiency and a voltage at a previous time point.

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

decrease the purge frequency when the voltage of the fuel cell stack becomes higher than that at a previous time point while the power generation efficiency of the fuel cell stack becomes lower than that at the previous time point.

9. A method for controlling purge of a fuel cell system, the method comprising: monitoring an operation state of a fuel cell stack;

determining a purge frequency based on the operation state; and

controlling a purge valve based on the determined purge frequency, the purge valve being configured to discharge hydrogen on a hydrogen supply line that passes the fuel cell stack,

wherein the controlling of the purge valve includes:

determining a first purge frequency, at which the power generation efficiency of the fuel cell stack reaches a maximum efficiency point,

wherein the controlling of the purge valve further includes:

searching for a second purge frequency, at which a changed maximum efficiency point is reached, while the purge frequency is adjusted in unit of a specific time period, when the maximum efficiency for the power generation efficiency of the fuel cell stack is changed to the changed maximum efficiency point during an operation thereof.

10. The method of claim 9 , wherein the monitoring of the operation state of the fuel cell stack includes:

monitoring at least one of a current, a voltage, a power generation efficiency, or a hydrogen supply amount of the fuel cell stack, or a combination thereof.

11. The method of claim 10 , wherein the monitoring of the operation state of the fuel cell stack further includes:

monitoring the operation state based on an average value for the operation state.

12. The method of claim 9 , wherein the searching of the second purge frequency includes:

adjusting the purge frequency while increasing or decreasing the purge frequency in unit of the specific time period based on a change in the power generation efficiency and a change in a voltage of the fuel cell stack.

13. The method of claim 12 , wherein the adjusting of the purge frequency includes:

increasing the purge frequency when the power generation efficiency and the voltage of the fuel cell stack become higher than a power generation efficiency and a voltage at a previous time point.

14. The method of claim 12 , wherein the adjusting of the purge frequency includes:

decreasing the purge frequency when the voltage of the fuel cell stack becomes lower than that at a previous time point while the power generation efficiency of the fuel cell stack becomes higher than that at the previous time point.

15. The method of claim 12 , wherein the adjusting of the purge frequency includes:

increasing the purge frequency when the power generation efficiency and the voltage of the fuel cell stack become lower than a power generation efficiency and a voltage at a previous time point.

16. The method of claim 12 , wherein the adjusting of the purge frequency includes:

decreasing the purge frequency when the voltage of the fuel cell stack becomes higher than that at a previous time point while the power generation efficiency of the fuel cell stack becomes lower than that at the previous time point.