Fuel cell system

Abstract

To provide a technique capable of appropriately controlling a negative voltage due to a cross leak and a negative voltage due to a hydrogen deficiency.SOLUTION: A fuel cell system includes: a fuel cell stack in which a plurality of fuel cells are stacked; an oxidant gas supply part that supplies an oxidant gas to the fuel cell stack; a fuel gas supply part that supplies a fuel gas to the fuel cell stack; a negative voltage detection part that detects generation of a negative voltage in at least one of the plurality of fuel cells; a current measurement part that measures an output current of the fuel cell stack; and a control part. The control part controls the oxygen gas supply part and the fuel gas supply part such that a flow rate of the oxygen gas and the fuel gas increase when generation of the negative voltage is detected and the output current is less than a predetermined threshold current, and limits the output current while controlling the fuel gas supply part such that the flow rate of the fuel gas increases when generation of the negative voltage is detected and the output current is equal to or more than a threshold current.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] In a fuel cell stack in which multiple fuel cells are stacked, a negative voltage may occur in some of the fuel cells due to a lack of hydrogen. Patent Document 1 describes a technology that stops the extraction of current from the fuel cell stack when a negative voltage is detected. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-283138 Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to hydrogen deficiency, negative voltage can also be caused by cross leakage, where hydrogen supplied to the anode side of the fuel cell permeates the electrolyte membrane and leaks to the cathode side. When negative voltage is caused by cross leakage, there is a problem in that the negative voltage cannot be resolved by current limiting. [Means for solving the problem]

[0005] The present disclosure has been made to solve the above-mentioned problems, and can be realized in the following forms.

[0006] According to an embodiment of the present disclosure, there is provided a fuel cell system comprising: a fuel cell stack including a plurality of stacked fuel cell cells; an oxidant gas supply unit that supplies an oxidant gas to the fuel cell stack; a fuel gas supply unit that supplies a fuel gas to the fuel cell stack; a negative voltage detection unit that detects the occurrence of a negative voltage in at least one of the plurality of fuel cell cells; a current measurement unit that measures an output current of the fuel cell stack; and a control unit that can limit the output current of the fuel cell stack and control the oxidant gas supply unit and the fuel gas supply unit. When the occurrence of the negative voltage is detected and the output current is less than a predetermined threshold current, the control unit controls the oxidant gas supply unit and the fuel gas supply unit to increase the flow rates of the oxidant gas and the fuel gas, and when the occurrence of the negative voltage is detected and the output current is equal to or greater than the threshold current, the control unit controls the fuel gas supply unit to increase the flow rate of the fuel gas while limiting the output current. In this type of fuel cell system, the control content is switched depending on whether the output current is less than the threshold current in the case of a negative voltage, so that appropriate control can be performed for both negative voltage due to cross leakage and negative voltage due to hydrogen deficiency.

[0007] The present disclosure can be realized in various forms, for example, a power generation device equipped with a fuel cell system, a vehicle equipped with a fuel cell system, a control method for a fuel cell system, etc. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of a fuel cell system; [Figure 2] 10 is a flowchart illustrating an example of a negative voltage process. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. First embodiment: 1 is a diagram showing a schematic configuration of a fuel cell system 100 according to one embodiment of the present disclosure. The fuel cell system 100 includes a fuel cell stack 10, a current measuring unit 21, a voltage measuring unit 22, an oxidant gas supplying unit 30, a fuel gas supplying unit 40, and a control unit 50. The fuel cell system 100 according to this embodiment is mounted on, for example, a fuel cell vehicle.

[0010] The fuel cell stack 10 is a polymer electrolyte fuel cell that generates electricity by receiving a supply of a fuel gas (e.g., hydrogen gas) and an oxidant gas (e.g., air) as reactant gases. The fuel cell stack 10 is configured by stacking a plurality of fuel cell units 11.

[0011] The current measuring unit 21 measures the current value of the output current of the fuel cell stack 10. The current measuring unit 21 transmits the measured current value to the control unit 50. The voltage measuring unit 22 is connected to each fuel cell 11 of the fuel cell stack 10, and measures the cell voltage, which is the voltage of each fuel cell 11. The voltage measuring unit 22 transmits the measurement result to the control unit 50. In this embodiment, the voltage measuring unit 22 transmits only the lowest cell voltage of the measured cell voltages to the control unit 50.

[0012] The oxidizing gas supply unit 30 supplies an oxidizing gas to the fuel cell stack 10. In this embodiment, the oxidizing gas supply unit 30 supplies air taken in from the outside to the fuel cell stack 10. The oxidizing gas supply unit 30 includes, for example, a pipe through which air flows, an air flow meter, a compressor, an on-off valve, and the like.

[0013] The fuel gas supply unit 40 supplies fuel gas to the fuel cell stack 10. In this embodiment, the fuel gas supply unit 40 supplies hydrogen gas from a fuel gas tank to the fuel cell stack 10. The fuel gas supply unit 40 includes, for example, pipes through which the hydrogen gas flows, an on-off valve, a regulator, an injector, and the like.

[0014] The control unit 50 is configured as a computer including a CPU, memory, and an interface circuit to which each component in the fuel cell system 100 is connected. The control unit 50 outputs signals for controlling the oxidant gas supply unit 30 and the fuel gas supply unit 40 and signals for limiting the output current of the fuel cell stack 10. The control unit 50 executes a control program stored in the memory to control the oxidant gas supply unit 30 and the fuel gas supply unit 40, thereby controlling the flow rates of the oxidant gas and the fuel gas. The control unit 50 also limits the output current of the fuel cell stack 10. The control unit 50 also functions as a negative voltage detection unit 51. However, some or all of the functions of these units may be realized by hardware circuits.

[0015] The negative voltage detection unit 51 detects the occurrence of a negative voltage in at least one fuel cell 11 among the plurality of fuel cell units 11. More specifically, the negative voltage detection unit 51 determines that a negative voltage has occurred when the cell voltage acquired from the voltage measurement unit 22 is equal to or lower than a predetermined threshold voltage. The predetermined threshold voltage is a negative voltage, for example, −0.3V.

[0016] 2 is a flowchart showing an example of negative voltage processing. This processing is performed by the control unit 50 when a negative voltage is detected by the negative voltage detection unit 51. The negative voltage processing is performed repeatedly, for example, while the fuel cell system 100 is in operation. The negative voltage processing is preferably performed even when the output current is 0 A. Furthermore, the negative voltage processing is preferably not performed when the ignition switch of the vehicle equipped with the fuel cell system 100 is turned off (ignition off).

[0017] In step S100, the control unit 50 determines whether the output current measured by the current measurement unit 21 is less than a predetermined threshold current. The threshold current is a current value of the output current that can determine whether the cause of the negative voltage is cross leakage. The threshold current can be determined in advance experimentally or empirically, and is, for example, greater than or equal to 0 A and less than or equal to 5 A. If the output current is less than the threshold current, the control unit 50 proceeds to processing in step S110. On the other hand, if the output current is greater than or equal to the threshold current, the control unit 50 proceeds to processing in step S115.

[0018] In step S110, the control unit 50 performs cross leak response processing. More specifically, the control unit 50 controls the oxidant gas supply unit 30 to increase the flow rate of the oxidant gas. For example, the control unit 50 sends a control signal to the compressor in the oxidant gas supply unit 30 to increase the rotation speed, and sends a control signal to the valve in the oxidant gas supply unit 30 to increase the opening degree. The control unit 50 also controls the fuel gas supply unit 40 to increase the flow rate of the fuel gas. For example, the control unit 50 sends a control signal to increase the drive cycle or valve opening time of the injector in the fuel gas supply unit 40. The cross leak response processing can eliminate the cross leak, and therefore the negative voltage.

[0019] In step S115, the control unit 50 performs hydrogen deficiency response processing. More specifically, the control unit 50 controls the fuel gas supply unit 40 to increase the flow rate of the fuel gas. The control unit 50 also limits the output current of the fuel cell stack 10. More specifically, the control unit 50 reduces the output current of the fuel cell stack 10 to a predetermined current limit value regardless of the output required by the external load. The hydrogen deficiency response processing can resolve the hydrogen deficiency, thereby eliminating the negative voltage.

[0020] In step S120, the control unit 50 determines whether the negative voltage has been eliminated. If the negative voltage has been eliminated, more specifically, if the negative voltage detection unit 51 does not detect a negative voltage, the control unit 50 ends the negative voltage processing. On the other hand, if the negative voltage has not been eliminated, more specifically, if the negative voltage detection unit 51 detects a negative voltage, the control unit 50 returns to the processing of step S100. In other words, the control unit 50 repeats the processing of steps S100 to S120 until the negative voltage is eliminated.

[0021] According to the fuel cell system 100 of the present embodiment described above, the control unit 50 switches the control content depending on whether the output current is equal to or greater than a threshold value in the case of a negative voltage. Therefore, appropriate control can be performed for both negative voltages due to cross leakage and negative voltages due to hydrogen deficiency. When the negative voltage is due to hydrogen deficiency, the control unit 50 performs current limitation, thereby eliminating the negative voltage. On the other hand, when the negative voltage is due to cross leakage, the negative voltage cannot be eliminated by current limitation, and therefore the control unit 50 does not perform current limitation. Furthermore, when the negative voltage is due to cross leakage, the control unit 50 controls the oxidant gas supply unit 30 and the fuel gas supply unit 40 to increase the flow rates of the oxidant gas and the fuel gas, thereby eliminating the cross leakage and eliminating the negative voltage. Therefore, the negative voltage can be eliminated whether the negative voltage is due to hydrogen deficiency or cross leakage.

[0022] B. Other Embodiments: In the above-described embodiment, the voltage measurement unit 22 transmits only the lowest cell voltage among the measured cell voltages to the control unit 50. However, this is not limiting, and the voltage measurement unit 22 may transmit all the measured cell voltages to the control unit 50. In this case, the control unit 50 executes negative voltage processing when the negative voltage detection unit 51 detects that one or more cell voltages are negative. Alternatively, the voltage measurement unit 22 may detect the voltage value of the entire fuel cell stack 10, and transmit to the control unit 50 an average cell voltage obtained by dividing the voltage value by the number of fuel cell units 11 included in the fuel cell stack 10.

[0023] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0024] 10... fuel cell stack, 11... fuel cell cell, 21... current measurement unit, 22... voltage measurement unit, 30... oxidant gas supply unit, 40... fuel gas supply unit, 50... control unit, 51... negative voltage detection unit, 100... fuel cell system

Claims

[Claim 1] 1. A fuel cell system, comprising: a fuel cell stack in which a plurality of fuel cell units 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 occurrence of a negative voltage in at least one fuel cell among the plurality of fuel cell units; a current measuring unit that measures the output current of the fuel cell stack; a control unit that can limit the output current of the fuel cell stack and control the oxidant gas supply unit and the fuel gas supply unit, The control unit when the generation of the negative voltage is detected and the output current is less than a predetermined threshold current, controlling the oxidant gas supply unit and the fuel gas supply unit so that the flow rates of the oxidant gas and the fuel gas are increased; When the occurrence of the negative voltage is detected and the output current is equal to or greater than the threshold current, the fuel cell system limits the output current while controlling the fuel gas supply unit so as to increase the flow rate of the fuel gas.

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