Fuel cell system and method of controlling fuel cell system

1. A fuel cell system comprising:

a fuel cell to generate electric power with heat;

a cathode off-gas discharge passage connected to the fuel cell, cathode off-gas discharged from the fuel cell to flow through the cathode off-gas discharge passage;

a sealing valve which is provided in the cathode off-gas discharge passage and to which the heat is transmitted from the fuel cell;

a first temperature sensor to detect a valve temperature of the sealing valve;

a refrigerant circulation circuit in which a refrigerant is to be circulated to cool the fuel cell;

a second temperature sensor provided in the refrigerant circulation circuit to detect a fuel cell temperature of the fuel cell through the refrigerant; and

circuitry configured:

to calculate a sealing valve estimated temperature by subtracting a correction value from the fuel cell temperature detected by the second temperature sensor after the fuel cell stops generating the electric power and after the sealing valve is closed;

to determine whether at least one of the valve temperature and the sealing valve estimated temperature is lower than a predicted freezing temperature; and

to open the sealing valve when it is determined that the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature.

2. The fuel cell system according to claim 1 , wherein the circuitry is configured

to calculate a difference value by subtracting the valve temperature from the fuel cell temperature before the fuel cell stops generating the power,

to determine whether the difference value is larger than an abnormality determination threshold,

to calculate the sealing valve estimated temperature after the fuel cell stops generating the power and after the sealing valve is closed, when it is determined that the difference value is larger than the abnormality determination threshold,

to determine whether the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature, when it is determined that the difference value is larger than the abnormality determination threshold, and

to determine whether the valve temperature is lower than the predicted freezing temperature after the fuel cell stops generating the power and after the sealing valve is closed, when it is determined that the difference value is not larger than the abnormality determination threshold.

3. The fuel cell system according to claim 1 , wherein the circuitry is configured

to determine whether or not the temperature of the sealing valve and the temperature of the fuel cell are correlated with each other upon receipt of a system stop signal,

to control the fuel cell to stop generating the power and to close the sealing valve to monitor at least one of the valve temperature and the sealing valve estimated temperature when it is determined that the temperature of the sealing valve and the temperature of the fuel cell are correlated with each other, and

to control the fuel cell to continue generating the power when it is determined that the temperature of the sealing valve and the temperature of the fuel cell are not correlated with each other.

4. The fuel cell system according to claim 1 , wherein the circuitry is configured to drive an air pump when the sealing valve is opened when it is determined that the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature.

5. The fuel cell system according to claim 1 ,

wherein the refrigerant circulation circuit supplies the refrigerant discharged from the fuel cell to the sealing valve, and

wherein the heat of the fuel cell is supplied to the sealing valve through the refrigerant.

6. The fuel cell system according to claim 1 , wherein the temperature of the sealing valve and the temperature of the fuel cell are correlated with each other.

7. A method of controlling a fuel cell system, comprising:

detecting a valve temperature of a sealing valve, the sealing valve being provided in a cathode off-gas discharge passage through which cathode off-gas discharged from a fuel cell is to flow, the fuel cell being to generate power with heat which is transmitted to the sealing valve;

detecting a fuel cell temperature of the fuel cell through a refrigerant to cool the fuel cell;

calculating a sealing valve estimated temperature that is an estimated temperature of the sealing valve by subtracting a correction value from the fuel cell temperature after the fuel cell stops generating the power and after the sealing valve is closed; and

determining whether at least one of the valve temperature and the sealing valve estimated temperature is lower than a predicted freezing temperature; and

opening the sealing valve when it is determined that the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature.

8. The method of controlling the fuel cell system according to claim 7 , further comprising:

calculating a difference value by subtracting the valve temperature from the fuel cell temperature before the fuel cell stops generating the power;

determining whether the difference value is larger than an abnormality determination threshold;

calculating the sealing valve estimated temperature after the fuel cell stops generating the power and after the sealing valve is closed, when it is determined that the difference value is larger than the abnormality determination threshold;

determining whether the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature, when it is determined that the difference value is larger than the abnormality determination threshold; and

determining whether the valve temperature is lower than the predicted freezing temperature after the fuel cell stops generating the power and after the sealing valve is closed, when it is determined that the difference value is not larger than the abnormality determination threshold.

9. The method of controlling the fuel cell system according to claim 7 , further comprising:

determining whether or not the temperature of the sealing valve and the temperature of the fuel cell are correlated with each other upon receipt of a system stop signal;

controlling the fuel cell to stop generating the power and to close the sealing valve to monitor at least one of the valve temperature and the sealing valve estimated temperature when it is determined that the temperature of the sealing valve and the temperature of the fuel cell are correlated with each other; and

controlling the fuel cell to continue generating the power when it is determined that the temperature of the sealing valve and the temperature of the fuel cell are not correlated with each other.

10. The method of controlling the fuel cell system according to claim 7 , further comprising driving an air pump when the sealing valve is opened when it is determined that the at least one of the valve temperature and the sealing valve estimated temperature is lower than the predicted freezing temperature.

11. The method of controlling the fuel cell system according to claim 7 ,

wherein the refrigerant circulation circuit supplies the refrigerant discharged from the fuel cell to the sealing valve, and

wherein the heat of the fuel cell is supplied to the sealing valve through the refrigerant.