Fuel cell system

A method for improving fuel gas consumption in power generation of fuel cells, wherein the fuel gas unused for the power generation is resupplied to the fuel cells through a fuel gas circulation system which includes a variable flow rate circulation pump operative to adjust a flow rate of the fuel gas circulating through the fuel gas circulation system and a valve for discharging the fuel gas in the fuel gas circulation system to the outside thereof, the method comprising:

• monitoring output voltages of the respective fuel cells;
• determining whether to increase the flow rate of the fuel gas in the fuel gas circulation system or to open the valve based on the monitored output voltages;
• controlling the variable flow rate circulation pump to increase flow rate of the fuel gas in the fuel gas circulation system, if some of the monitored output voltages are out of a predetermined range which includes an average value of the output voltages of the respective fuel cells;
• and
• opening the valve to discharge the fuel gas out of the fuel gas circulation system, if some of the monitored output voltages are within the predetermined range and the average value of the output voltages of the respective fuel cells is lower than a predetermined value.

A fuel cell system comprising:

• a fuel cell to be supplied with a gas for power generation, the gas unused for the power generation to be discharged out of the fuel cell;
• a circulation flow path through which the gas discharged out of the fuel cell is resupplied to the fuel cell;
• a variable flow rate circulation pump for circulating the gas through the circulation flow path, which is operative to adjust a flow rate of the gas in the circulation flow path;
• a valve for discharging the gas in the circulation flow path to the outside of the circulation flow path;
• a voltage sensor for measuring voltage of the fuel cell;
• and
• a controller for controlling the circulation pump and the valve,
• wherein the controller is configured to control the circulation pump to increase the flow rate of the gas in the circulation flow path if the voltage measured by the voltage sensor becomes lower than a predetermined value, and to open the valve thereafter if the voltage measured by the voltage sensor does not recover to the predetermined value.

A method of controlling a fuel cell system comprising:

• a fuel cell to be supplied with a gas for power generation, the gas unused for the power generation to be discharged out of the fuel cell;
• a circulation flow path through which the gas discharged out of the fuel cell is resupplied to the fuel cell;
• a variable flow rate circulation pump for circulating the gas through the circulation flow path, whose speed is adjustable to adjust a now rate of the gas in the circulation flow path;
• a valve for discharging the gas in the circulation flow path to the outside of the circulation flow path;
• and
• a voltage sensor for measuring voltage of the fuel cell;
• the method comprising:
• determining whether to increase the speed of the circulation pump or to open the valve based on the voltage measured by the voltage sensor.

A method of controlling a fuel cell system comprising:

• a fuel cell to be supplied with a gas for power generation, the gas unused for the power generation to be discharged out of the fuel cell;
• a circulation flow path through which the gas discharged out of the fuel cell is resupplied to the fuel cell;
• a variable flow rate circulation pump for circulating the gas through the circulation flow path, whose speed is adjustable to adjust a flow rate of the gas in the circulation flow path;
• a valve for discharging the gas in the circulation flow path to the outside of the circulation flow path;
• and
• a voltage sensor for measuring voltage of the fuel cell,
• the method comprising:
• increasing the speed of the circulation pump if the voltage measured by the voltage sensor becomes lower than a predetermined value;
• and
• opening the valve thereafter if the voltage measured by the voltage sensor does not recover to the predetermined value.