Fuel cell system

Abstract

The invention provides a fuel cell system which can perform appropriate control according to negative voltage caused by cross leakage and negative voltage caused by hydrogen deficiency. A fuel cell system is provided with: a fuel cell stack in which a plurality of fuel cell cells are stacked; an oxidant gas supply unit that supplies an oxidant gas to the fuel cell stack; a fuel gas supply unit that supplies fuel gas to the fuel cell stack; a negative voltage detection unit that detects the generation of a negative voltage in at least one of the plurality of fuel cell cells; a current measurement unit that measures the output current of the fuel cell stack; and a control unit. The control unit controls the oxidant gas supply unit and the fuel gas supply unit such that the flow rates of the oxidant gas and the fuel gas increase when the generation of the negative voltage is detected and the output current is less than a predetermined threshold current, and controls the oxidant gas supply unit and the fuel gas supply unit such that the flow rates of the oxidant gas and the fuel gas increase when the generation of the negative voltage is detected and the output current is equal to or greater than the threshold current. The control unit limits the output current while controlling the fuel gas supply unit so that the flow rate of the fuel gas increases.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a fuel cell system. BACKGROUND

[0002] In a fuel cell stack in which a plurality of fuel cell units are stacked, there is a case where a negative voltage is generated in a part of the fuel cell units due to a lack of hydrogen. In Patent Literature 1, there is described a technique in which, in a case where a negative voltage is detected, the current taken out from the fuel cell stack is stopped.

[0003] Patent Literature 1: Japanese Patent Application Publication No. 2009-283138

[0004] As a cause of the negative voltage, in addition to the lack of hydrogen, there is a cross leakage in which hydrogen supplied to the anode side of the fuel cell leaks to the cathode side through the electrolyte membrane. In a case where the negative voltage is caused by the cross leakage, there is a problem that the negative voltage cannot be eliminated due to current limitation. SUMMARY

[0005] The present disclosure is achieved in order to solve the above-described problems, and can be implemented as the following technical solution.

[0006] According to the technical solution of the present disclosure, there is provided a fuel cell system. The fuel cell system includes: a fuel cell stack in which a plurality of fuel cell units are stacked; an oxidant gas supply portion that supplies an oxidant gas to the fuel cell stack; a fuel gas supply portion that supplies a fuel gas to the fuel cell stack; a negative voltage detection portion that detects generation of a negative voltage in at least one of the plurality of fuel cell units; a current measurement portion that measures an output current of the fuel cell stack; and a control portion that is capable of performing limitation of the output current of the fuel cell stack and control of the oxidant gas supply portion and the fuel gas supply portion. In a case where the generation of the negative voltage is detected and the output current is smaller than a threshold current decided in advance, the control portion controls the oxidant gas supply portion and the fuel gas supply portion in a manner that the flow rates of the oxidant gas and the fuel gas are increased, and in a case where the generation of the negative voltage is detected and the output current is equal to or larger than the threshold current, the control portion controls the fuel gas supply portion in a manner that the flow rate of the fuel gas is increased while limiting the output current.

[0007] According to the fuel cell system of this manner, in a case where a negative voltage occurs, the control content is switched depending on whether the output current is smaller than the threshold current, and thus appropriate control can be performed for the negative voltage caused by the cross leakage and the negative voltage caused by the lack of hydrogen, respectively.

[0008] Further, the present disclosure can be implemented in various ways, for example, as a power generation device provided with a fuel cell system, a vehicle provided with a fuel cell system, a control method for a fuel cell system, and the like. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a diagram showing a brief configuration of a fuel cell system.

[0010] Figure 2 is a flowchart showing one example of negative voltage processing.

[0011] EXPLANATION OF REFERENCE NUMERALS

[0012] 10…fuel cell stack; 11…fuel cell cell; 21…current measurement section; 22…voltage measurement section; 30…oxidant gas supply section; 40…fuel gas supply section; 50…control section; 51…negative voltage detection section; 100…fuel cell system. DETAILED DESCRIPTION

[0013] A. First Embodiment:

[0014] Figure 1 is a diagram showing a brief configuration of a fuel cell system 100 in one embodiment of the present disclosure. The fuel cell system 100 is provided with a fuel cell stack 10, a current measurement section 21, a voltage measurement section 22, an oxidant gas supply section 30, a fuel gas supply section 40, and a control section 50. The fuel cell system 100 of the present embodiment is mounted on a fuel cell vehicle, for example.

[0015] The fuel cell stack 10 is a solid polymer fuel cell that generates electricity by accepting supply of a fuel gas (for example, hydrogen) and an oxidant gas (for example, air) as reaction gases. The fuel cell stack 10 is configured by stacking a plurality of fuel cell cells 11.

[0016] The current measurement section 21 measures a current value of an output current of the fuel cell stack 10. The current measurement section 21 transmits the measured current value to the control section 50. The voltage measurement section 22 is connected to each fuel cell cell 11 of the fuel cell stack 10, and measures a voltage of each fuel cell cell 11, that is, a cell voltage. The voltage measurement section 22 transmits the measurement result to the control section 50. In the present embodiment, the voltage measurement section 22 transmits only the lowest cell voltage among the measured cell voltages to the control section 50.

[0017] The oxidant gas supply section 30 performs supply of an oxidant gas to the fuel cell stack 10. In the present embodiment, the oxidant gas supply section 30 supplies air taken in from the outside to the fuel cell stack 10. The oxidant gas supply section 30 has a pipe through which air flows, an air flow meter, a compressor, an on-off valve, and the like, for example.

[0018] The fuel gas supply portion 40 performs supply of fuel gas to the fuel cell stack 10. In the present embodiment, the fuel gas supply portion 40 supplies hydrogen gas to the fuel cell stack 10 from a fuel gas tank. The fuel gas supply portion 40 has, for example, a pipe through which hydrogen gas flows, an opening and closing valve, a regulator, an injector, and the like.

[0019] The control portion 50 is configured as a computer that has a CPU, a memory, and an interface circuit to which the respective portions in the fuel cell system 100 are connected. The control portion 50 outputs a signal for controlling the oxidant gas supply portion 30 and the fuel gas supply portion 40 and a signal for limiting the output current of the fuel cell stack 10. The control portion 50 controls the oxidant gas supply portion 30 and the fuel gas supply portion 40 by executing a control program stored in the memory, and performs control of the flow rates of the oxidant gas and the fuel gas. In addition, the control portion 50 performs limitation of the output current of the fuel cell stack 10. In addition, the control portion 50 realizes the function as the negative voltage detection portion 51. However, a part or all of the functions of the respective portions described above can also be realized by a hardware circuit.

[0020] The negative voltage detection portion 51 detects generation of a negative voltage in at least one of the plurality of fuel cell cells 11. More specifically, in a case where the cell voltage acquired from the voltage measurement portion 22 is equal to or lower than a threshold voltage decided in advance, the negative voltage detection portion 51 determines that a negative voltage is generated. The threshold voltage decided in advance is a negative voltage, for example, -0.3 V.

[0021] Figure 2 is a flowchart showing one example of negative voltage processing. This processing is processing performed by the control portion 50 in a case where a negative voltage is detected by the negative voltage detection portion 51. The negative voltage processing is repeatedly performed, for example, during operation of the fuel cell system 100. It is preferable that the negative voltage processing be performed even if the output current is 0 A. In addition, it is preferable that the negative voltage processing not be performed in a state where an ignition switch of a vehicle on which the fuel cell system 100 is mounted is turned off (ignition is turned off).

[0022] In step S100, the control portion 50 determines whether or not the output current measured by the current measurement portion 21 is less than a threshold current decided in advance. The threshold current is a current value of the output current by which it is possible to determine whether or not a cause of a negative voltage is cross leakage. The threshold current can be determined in advance through experiments or experience, for example, 0 A or more and 5 A or less. In a case where the output current is less than the threshold current, the control portion 50 proceeds to the processing of step S110. On the other hand, in a case where the output current is the threshold current or more, the control portion 50 proceeds to the processing of step S115.

[0023] In step S110, the control section 50 performs cross leakage countermeasure processing. More specifically, the control section 50 controls the oxidant gas supply section 30 in such a manner that the flow rate of the oxidant gas increases. For example, the control section 50 sends a control signal to the compressor in the oxidant gas supply section 30 in such a manner that the rotational speed increases, and sends a control signal in such a manner that the opening degree of the valve in the oxidant gas supply section 30 increases. In addition, the control section 50 controls the fuel gas supply section 40 in such a manner that the flow rate of the fuel gas increases. For example, the control section 50 sends a control signal in such a manner that the driving period of the injector, the valve opening time in the fuel gas supply section 40 lengthens. With the cross leakage countermeasure processing, the cross leakage can be eliminated, and thus the negative voltage can be eliminated.

[0024] In step S115, the control section 50 performs hydrogen deficiency countermeasure processing. More specifically, the control section 50 controls the fuel gas supply section 40 in such a manner that the flow rate of the fuel gas increases. In addition, the control section 50 limits the output current of the fuel cell stack 10. More specifically, regardless of the required output from the external load, the control section 50 reduces the output current of the fuel cell stack 10 to a predetermined current limit value. With the hydrogen deficiency countermeasure processing, the hydrogen deficiency can be eliminated, and thus the negative voltage can be eliminated.

[0025] In step S120, the control section 50 determines whether the negative voltage is eliminated. In the case where the negative voltage is eliminated, more specifically, in the case where the negative voltage detection section 51 does not detect the negative voltage, the control section 50 ends the negative voltage processing. On the other hand, in the case where the negative voltage is not eliminated, more specifically, in the case where the negative voltage detection section 51 detects the negative voltage, the control section 50 returns to the processing of step S100. That is, the control section 50 repeatedly performs the processing of steps S100 to S120 until the negative voltage is eliminated.

[0026] According to the fuel cell system 100 of the above-described embodiment, the control section 50 switches the control content depending on whether the output current is equal to or greater than the threshold value in the case of the negative voltage, and thus can perform appropriate control for the negative voltage caused by the cross leakage and the negative voltage caused by the hydrogen deficiency, respectively. In the case where the cause of the negative voltage is the hydrogen deficiency, the control section 50 performs the current limitation, and thus the negative voltage can be eliminated. On the other hand, in the case where the cause of the negative voltage is the cross leakage, the negative voltage cannot be eliminated by the current limitation, and thus the control section 50 does not perform the current limitation. In addition, in the case where the cause of the negative voltage is the cross leakage, the control section 50 controls the oxidant gas supply section 30 and the fuel gas supply section 40 in such a manner that the flow rates of the oxidant gas and the fuel gas increase, and thus the cross leakage is eliminated, and the negative voltage can be eliminated. Therefore, regardless of whether the cause of the negative voltage is the hydrogen deficiency or the cross leakage, the negative voltage can be eliminated.

[0027] B. Other Embodiments:

[0028] In the above-described embodiment, the voltage measurement section 22 transmits only the lowest cell voltage among the measured cell voltages to the control section 50. This is not restrictive, and the voltage measurement section 22 can transmit all of the measured cell voltages to the control section 50. In this case, in a case where the negative voltage detection section 51 detects one or more cell voltages as negative voltages, the control section 50 executes the negative voltage processing. In addition, the voltage measurement section 22 can detect a voltage value of the entire fuel cell stack 10, and transmit an average cell voltage obtained by dividing the number of fuel cell cells 11 possessed by the fuel cell stack 10 to the control section 50.

[0029] The present disclosure is not limited to the above-described embodiment, and can be implemented in various structures without departing from the gist thereof. For example, in order to solve the above-described problem, or in order to achieve part or all of the above-described effects, the technical features in the embodiments corresponding to the technical features in each of the modes recited in the column of the summary of the application can be appropriately replaced, combined. In addition, as long as the technical features are not described as essential technical features in the present specification, they can be appropriately deleted.

Claims

1. A fuel cell system, wherein, Possess: a fuel cell stack in which a plurality of fuel cell units are stacked; an oxidizing gas supply portion that supplies oxidizing gas to the fuel cell stack; a fuel gas supply portion that supplies fuel gas to the fuel cell stack; a negative voltage detection portion that detects generation of a negative voltage in at least one of the plurality of fuel cell units; a current measurement portion that measures an output current of the fuel cell stack; and a control portion that is capable of performing restriction of the output current of the fuel cell stack and control of the oxidizing gas supply portion and the fuel gas supply portion, in a case where generation of the negative voltage is detected and the output current is less than a threshold current decided in advance, the control portion controls the oxidizing gas supply portion and the fuel gas supply portion so that the flow rates of the oxidizing gas and the fuel gas increase, in a case where generation of the negative voltage is detected and the output current is the threshold current or more, the control portion controls the fuel gas supply portion so that the flow rate of the fuel gas increases while restricting the output current.

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