Fuel cell system and control method therefor

A fuel cell system that outputs electric power in response to a request from an external load, comprising:

• a fuel cell that has at least one power generating element;
• a reaction gas supply unit that supplies reaction gas to the fuel cell;
• a negative voltage detecting unit that detects negative voltage in the at least one power generating element;
• a control unit that controls electric power output from the fuel cell;
• and
• an accumulated current value measuring unit that measures an accumulated current value that is obtained by time integration of current output from the fuel cell, wherein
• when negative voltage is generated in the at least one power generating element, the control unit executes recovery process of increasing an amount of supplied reaction gas in order to recover from the negative voltage,
• the control unit prestores a correlation between an accumulated current value in a negative voltage generation period during which the negative voltage is generated in the at least one power generating element and a current density at or below which the at least one power generating element can recover from the negative voltage through the recovery process, and
• when negative voltage has been detected in the at least one power generating element, the control unit uses the correlation to execute output restricting process of causing the fuel cell to output electric power at a current density that is lower than or equal to a current density obtained in correspondence with the accumulated current value in the negative voltage generation period.

A fuel cell system that outputs electric power in response to a request from an external load, comprising:

• a fuel cell that has at least one power generating element;
• a negative voltage detecting unit that detects negative voltage in the at least one power generating element;
• a control unit that controls electric power output from the fuel cell;
• and
• an accumulated current value measuring unit that measures an accumulated current value that is obtained by time integration of current output from the fuel cell, wherein
• when negative voltage has been detected in the at least one power generating element, the control unit interrupts electrical connection between the external load and the fuel cell and then executes reconnection process of electrically connecting the fuel cell to the external load again, and
• in the reconnection process, the control unit sets an interval time from when electrical connection between the fuel cell and the external load is interrupted to when the fuel cell is connected to the external load again on the basis of an accumulated current value in an oxygen generation period during which negative voltage is generated in the at least one power generating element and oxygen is produced by water-splitting reaction in the anode of the at least one power generating element.

A fuel cell system that outputs electric power in response to a request from an external load, comprising:

• a fuel cell that has at least one power generating element;
• a negative voltage detecting unit that measures a voltage of the at least one power generating element to detect negative voltage;
• a control unit that controls electric power output from the fuel cell;
• an accumulated current value measuring unit that measures an accumulated current value that is obtained by time integration of current output from the fuel cell;
• and
• a reaction gas supply unit that supplies reaction gas to the fuel cell, wherein
• when negative voltage has been detected in the at least one power generating element, the control unit decreases a current density of the fuel cell within a preset range and detects a variation in voltage of the at least one power generating element, in which negative voltage is generated, before and after the current density is decreased, and, when the variation in voltage falls within a predetermined allowable range, the control unit further decreases the current density of the fuel cell and increases an amount of reaction gas supplied to the fuel cell;
• whereas, when the variation in voltage falls outside the predetermined allowable range, the control unit increases the amount of reaction gas supplied to the fuel cell without decreasing the current density of the fuel cell.

A control method for a fuel cell system that has a fuel cell having at least one power generating element, comprising:

• determining whether there is a possibility that negative voltage is generated in the at least one power generating element;
• measuring an accumulated current value in an oxygen generation period during which there is a possibility that negative voltage is generated in the at least one power generating element and oxygen is produced by water-splitting reaction in an anode of the at least one power generating element;
• consulting a preset first correlation between a predetermined value based on the accumulated current value in the oxygen generation period and an oxygen consumption rate at which oxygen is recombined with hydrogen to be consumed in the anode of the at least one power generating element in which negative voltage is generated and a preset second correlation between a current density of the fuel cell in the oxygen generation period and an oxygen production rate at which oxygen is produced in the anode of the at least one power generating element in which negative voltage is generated in the oxygen generation period;
• and
• obtaining an oxygen consumption rate using the first correlation and obtaining a current density corresponding to an oxygen production rate equivalent to the oxygen consumption rate obtained from the first correlation using the second correlation, and executing output restricting process of causing the fuel cell to output electric power at a current density that is lower than the obtained current density corresponding to the oxygen production rate.