FUEL CELL SYSTEM AND METHOD FOR CONTROLLING THE SAME

1 . A method for controlling a fuel cell system including a fuel cell and a secondary battery for storing output power of the fuel cell,

the method comprising the steps of:

detecting a remaining capacity of the secondary battery;

determining a rate of change of the remaining capacity, where the rate of change is defined as positive when it increases and negative when it decreases; and

changing an operation state of the fuel cell based on the remaining capacity and the rate of change.

2 . The method for controlling a fuel cell system in accordance with claim 1 , wherein the step of changing the operation state is a step of switching the operation state between a plurality of power generation modes based on the remaining capacity and the rate of change.

3 . The method for controlling a fuel cell system in accordance with claim 2 ,

wherein the power generation modes are switched based on a result of comparison between the remaining capacity and at least one reference value, and

control modes each having the at least one reference value for controlling the operation state of the fuel cell are switched based on a result of comparison between the rate of change and at least one predetermined value.

4 . The method for controlling a fuel cell system in accordance with claim 3 ,

wherein the remaining capacity is divided by N of the at least one reference value into (N+1) ranges where N is an integer of 1 or more, and

each of (N+1) of the power generation modes is set for each of the (N+1) ranges of the remaining capacity such that amounts of power generated by the power generation modes increase as the remaining capacity decreases.

5 . The method for controlling a fuel cell system in accordance with claim 4 ,

wherein the rate of change is divided by M of the at least one predetermined value into (M+1) ranges where M is an integer of 1 or more, and

each of (M+1) of the control modes is set for each of the (M+1) ranges of the rate of change such that the respective (N+1) reference values of the control modes decrease as the rate of change increases.

6 . The method for controlling a fuel cell system in accordance with claim 1 , wherein the remaining capacity is detected based on a voltage of the secondary battery.

7 . The method for controlling a fuel cell system in accordance with claim 6 , wherein the voltage of the secondary battery is detected based on a terminal voltage of a capacitor connected to the secondary battery in parallel.

8 . The method for controlling a fuel cell system in accordance with claim 1 ,

wherein the step of changing the operation state is a step of changing a control mode for controlling the operation state of the fuel cell continuously or in stages, and

the fuel cell is more likely to be operated in a power generation mode for generating a larger amount of power as an absolute value of the positive rate of change decreases or as an absolute value of the negative rate of change increases.

9 . The method for controlling a fuel cell system in accordance with claim 8 , wherein the power generation mode is changed continuously or in stages such that the amount of power generation increases as the remaining capacity decreases.

10 . A fuel cell system comprising:

a fuel cell;

a secondary battery for storing output power of the fuel cell;

a remaining capacity detector for detecting a remaining capacity of the secondary battery; and

a controller for determining a rate of change of the remaining capacity, where the rate of change is defined as positive when it increases and negative when it decreases, and changing an operation state of the fuel cell based on the remaining capacity and the rate of change.

11 . The fuel cell system in accordance with claim 10 , wherein the controller is configured to switch the operation state between a plurality of power generation modes based on the remaining capacity and the rate of change.

12 . The fuel cell system in accordance with claim 11 , wherein the controller is configured to:

switch the power generation modes based on a result of comparison between the remaining capacity and at least one reference value; and

switch control modes, each having the at least one reference value for controlling the operation state of the fuel cell, based on a result of comparison between the rate of change and at least one predetermined value.

13 . The fuel cell system in accordance with claim 12 ,

wherein the remaining capacity is divided by N of the at least one reference value into (N+1) ranges where N is an integer of 1 or more, and

each of (N+1) of the power generation modes is set for each of the (N+1) ranges of the remaining capacity such that amounts of power generated by the power generation modes increase as the remaining capacity decreases.

14 . The fuel cell system in accordance with claim 13 ,

wherein the rate of change is divided by M of the at least one predetermined value into (M+1) ranges where M is an integer of 1 or more, and

each of (M+1) of the control modes is set for each of the (M+1) ranges of the rate of change such that the respective (N+1) reference values of the control modes decrease as the rate of change increases.

15 . The fuel cell system in accordance with claim 10 , wherein the controller changes a control mode for controlling the operation state of the fuel cell continuously or in stages such that the fuel cell is more likely to be operated in a power generation mode for generating a larger amount of power as an absolute value of the positive rate of change decreases or as an absolute value of the negative rate of change increases.

16 . The fuel cell system in accordance with claim 15 , wherein the controller changes the power generation mode continuously or in stages such that the amount of power generation increases as the remaining capacity decreases.