Fuel Cell Systems

Abstract

To provide a fuel battery system capable of improving accuracy of performance degradation determination of a fuel battery.SOLUTION: A fuel battery 10 is made of a plurality of laminated fuel battery 10 cells for generating power when fuel gas and oxidant gas are supplied to one surface and the other surface of an MEA including an electrolyte membrane, respectively. A voltage detection section 31 detects a voltage value output by the fuel battery 10. A current detection section 32 detects a current value extracted from the fuel battery 10. An ECU 100 as a battery deterioration detection section detects deterioration of the fuel battery 10 on the basis of relation between "a preceding maximum current value," the maximum value of current values detected by the current detection section 32 within a predetermined time immediately before the fuel battery 10 executes power generation of a predetermined load, and "an execution time voltage value," a voltage value detected by the voltage detection section 31 when the fuel battery 10 executes power generation of the predetermined load.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a fuel cell system mounted on a vehicle or the like. [Background technology]

[0002] Conventionally, fuel cells have been known that are constructed by stacking a plurality of fuel cell units, each of which generates electricity by supplying a fuel gas as an anode gas and an oxidant gas as a cathode gas to one side and the other side of an MEA including an electrolyte membrane. Note that MEA is an abbreviation for Membrane Electrode Assembly, and is a membrane electrode assembly that includes an electrolyte membrane and an electrode catalyst layer.

[0003] Patent Document 1 discloses a technology related to a determination device for determining the performance degradation state of a fuel cell. This determination device determines the performance degradation state of a fuel cell by comparing the impedance when a predetermined high frequency is applied to the fuel cell with a determination reference value that is determined according to the operating state of the fuel cell. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-48559 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology described in Patent Document 1, when determining the performance degradation of a fuel cell, the operating conditions of the fuel cell, such as the internal temperature of the fuel cell, the wetness state of the MEA, the activity state of the catalyst, the humidification amount, flow rate, pressure, and diffusion state of the supply gas, must be appropriately detected. However, it is generally difficult to detect all of the operating conditions of the fuel cell required for determining the performance degradation of the fuel cell. Therefore, there is a concern that the determination device described in Patent Document 1 will have low accuracy in determining the performance degradation of the fuel cell.

[0006] In view of the above, an object of the present invention is to provide a fuel cell system that is capable of improving the accuracy of determining performance degradation of a fuel cell. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention relates to a fuel cell system, a fuel cell (10) in which a plurality of fuel cell units (C) are stacked, each of which generates electricity by supplying a fuel gas as an anode gas and an oxidant gas as a cathode gas to one side and the other side of a membrane electrode assembly (hereinafter referred to as "MEA") including an electrolyte membrane; a voltage detection unit (31) that detects a voltage value output by the fuel cell; a current detection unit (32) for detecting a value of a current taken from the fuel cell; The fuel cell is provided with a cell degradation detection unit (100) that detects degradation of the fuel cell based on the relationship between a "previous maximum current value," which is the maximum current value detected by the current detection unit within a specified time immediately before the fuel cell generates a specified load, and an "execution voltage value," which is a voltage value detected by the voltage detection unit when the fuel cell generates a specified load.

[0008] According to this, as a result of extensive research, the inventors have discovered that in an initial state of a fuel cell, there is no trend between the "previous maximum current value" and the "runtime voltage value", but as the fuel cell deteriorates over time, there gradually emerges a tendency for the "runtime voltage value" to become smaller as the "previous maximum current value" becomes smaller.

[0009] Specifically, when the "last maximum current value" is small, this means that low-load power generation was performed within a specified time period immediately prior to the execution of power generation at a specified load (hereinafter, simply referred to as "within the immediately preceding specified time period"). During low-load power generation, the flow rate of cathode gas is small, so depending on the deterioration state of the fuel cell, the power generation state may be such that water is likely to accumulate in the MEA.

[0010] However, in a fuel cell in the initial state, the MEA has good drainage properties, so the MEA is in a moderately wet state even when the flow rate of the cathode gas is low, such as during low-load power generation. Therefore, in a fuel cell in the initial state, when power generation is performed at a specified load, regardless of the previous maximum current value, the MEA is in a moderately wet state, and the power generation state is good, with good proton conductivity and a relatively high voltage value. Therefore, in a fuel cell in the initial state, there is no tendency between the "previous maximum current value" and the "runtime voltage value".

[0011] In contrast, as a fuel cell deteriorates over time, the drainage properties of the MEA gradually deteriorate. Therefore, when the flow rate of cathode gas is low, such as during low-load power generation, if the drainage properties of the MEA deteriorate due to deterioration of the fuel cell over time, water generated during power generation is not drained from the MEA, and the MEA is likely to accumulate (i.e., flooded). In this way, in a fuel cell that has deteriorated over time, the smaller the "previous maximum current value," the more likely water is to accumulate in the MEA. Therefore, when power generation is subsequently performed at a specified load, the water accumulated in the MEA will hinder the supply of cathode gas to the catalyst, resulting in a power generation state with a low "runtime voltage value."

[0012] On the other hand, if the "last maximum current value" is large, it means that high-load power generation was performed within the previous specified time. Since the flow rate of the cathode gas is large during high-load power generation, even if the drainage of the MEA has deteriorated due to aging of the fuel cell, the water generated during power generation is discharged from the MEA by the cathode gas, and the MEA is in a moderately wet state. Therefore, even if the fuel cell has deteriorated with age, if the "last maximum current value" is large, the proton conductivity of the MEA will be good when power generation of a specified load is performed thereafter, and the "runtime voltage value" will be high, resulting in a good power generation state. Therefore, as the fuel cell deteriorates with age from the initial state, a tendency gradually occurs that the smaller the "last maximum current value" is, the smaller the "runtime voltage value" is.

[0013] Therefore, in the invention according to claim 1, deterioration of the fuel cell is detected based on the relationship between the "previous maximum current value" and the "runtime voltage value." That is, as described above, as a fuel cell deteriorates over time from its initial state, a tendency gradually arises in which the smaller the "previous maximum current value," the smaller the "runtime voltage value," making it possible to detect deterioration of the fuel cell. Therefore, the fuel cell system according to claim 1 can accurately determine deterioration of the fuel cell without detecting various operating states of the fuel cell as in the determination device described in Patent Document 1.

[0014] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a schematic configuration of a fuel cell system according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a control system of the fuel cell system. [Diagram 3] This data is obtained by detecting the "runtime voltage value" and the "immediately preceding maximum current value" multiple times when the fuel cell performs a predetermined medium load power generation during a predetermined period in the initial state of the fuel cell. [Figure 4] This data is obtained by detecting the "runtime voltage value" and the "previous maximum current value" multiple times when the fuel cell generates a predetermined medium load power during a predetermined period of time after a predetermined time has elapsed since the initial state of the fuel cell. [Diagram 5] 5 is a graph for explaining a method for creating the data of FIGS. 3 and 4. [Figure 6] 4 is a flowchart of a degradation determination and degradation recovery process executed by an electronic control device included in the fuel cell system according to the first embodiment. [Figure 7] 5 is a graph showing the relationship between the slope of the graph in FIG. 4 and the power generation load at which flooding occurs. [Figure 8A]10 is a flowchart of a degradation determination and degradation recovery process executed by an electronic control device included in a fuel cell system according to a second embodiment. [Figure 8B] 8B is a flowchart continuing from FIG. 8A, showing the degradation determination and degradation recovery processing executed by the electronic control device included in the fuel cell system according to the second embodiment. [Figure 8C] 8B is a flowchart continuing from FIG. 8A, showing the degradation determination and degradation recovery processing executed by the electronic control device included in the fuel cell system according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals, and the description thereof will be omitted.

[0017] (First embodiment) A first embodiment will be described with reference to Figures 1 to 6. In this embodiment, an example will be described in which the fuel cell system of the present disclosure is applied to a vehicle FCEV that obtains electric power from a fuel cell 10 to supply to a motor for driving the vehicle. FCEV is an abbreviation for Fuel Cell Electric Vehicle.

[0018] The fuel cell system includes a fuel cell 10 that generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen, which are reactant gases. The fuel cell 10 supplies electric power to a power conversion device 13, such as an inverter 11 and a DC-DC converter 12. The inverter 11 converts the direct current supplied from the fuel cell 10 into alternating current, and supplies it to a load device 14, such as a driving motor, to drive the load device 14.

[0019] The DC-DC converter 12 is connected to an electrical storage device 15. The fuel cell system is configured such that surplus power out of the power output from the fuel cell 10 is stored in the electrical storage device 15 via the DC-DC converter 12.

[0020] The fuel cell 10 is configured as a cell stack CS in which a plurality of fuel cells C, which are the smallest units, are stacked. The fuel cells C have a cell surface that extends in a direction perpendicular to the stacking direction of the fuel cells C. The fuel cells C are configured as solid polymer electrolyte fuel cells (so-called PEFC) having an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator. The electrolyte membrane, catalyst layer, and gas diffusion layer constitute an MEA. In the fuel cell C, the MEA is sandwiched between separators. When a fuel gas (specifically, hydrogen) is supplied as an anode gas to the anode electrode side of the MEA and an oxidant gas (specifically, oxygen contained in the air) is supplied as a cathode gas to the cathode electrode side of the MEA, electrochemical reactions shown in the following reaction formulas F1 and F2 occur to generate electric energy. Anode electrode side: H2 → 2H + +2e - (F1) Cathode electrode side: 2H + +1 / 2O2+2e - →H2O···(F2)

[0021] For the above electrochemical reaction to occur, the MEA of the fuel cell C must be in a wet state containing water. The fuel cell system humidifies the MEA inside the fuel cell 10. The MEA can be humidified by arranging a humidifier or the like in the supply path of hydrogen, which is the fuel gas, or air, which is the oxidant gas.

[0022] The fuel cell system includes a cathode gas supply path 20 that supplies air containing oxygen toward the fuel cell 10, and a cathode gas discharge path 21 that discharges off-air used in the fuel cell 10. An air pump 22 is provided in the cathode gas supply path 20. The air pump 22 is configured by, for example, a turbo compressor. The air pump 22 has its capacity to supply air to the fuel cell 10 controlled based on a control signal from an electronic control device 100, which will be described later. An air valve 23 is provided in the cathode gas discharge path 21.

[0023] The fuel cell system also includes an anode gas supply path 40 that supplies hydrogen to the fuel cell 10, an anode gas discharge path 41 that discharges hydrogen off-gas (i.e., off-fuel) used in the fuel cell 10, and a circulation path 42 that circulates the off-fuel flowing through the anode gas discharge path 41 to the anode gas supply path 40. A high-pressure hydrogen tank 43, which is a hydrogen supply source, is provided at the most upstream portion of the anode gas supply path 40. A fuel valve 44 is provided in the anode gas supply path 40. A gas-liquid separator 45 provided in the middle of the anode gas discharge path 41 separates liquid water from the off-fuel and stores the water. The stored water in the gas-liquid separator 45 is discharged from the anode gas discharge path 41. An exhaust valve 46 is provided in the anode gas discharge path 41. The downstream side of the anode gas discharge path 41 and the downstream side of the cathode gas discharge path 21 are connected to a muffler of the vehicle.

[0024] Next, the control system of the fuel cell system will be described with reference to Figures 1 and 2. The fuel cell system includes an electronic control unit 100 (hereinafter referred to as "ECU 100"). The ECU 100 includes a microcomputer including a processor and memory and its peripheral circuits. The memory of the ECU 100 is a non-transient physical storage medium.

[0025] Based on a control program stored in the memory, the ECU 100 operates controlled devices connected to the output side to control the operation of the fuel cell 10. Specifically, the output side of the ECU 100 is connected to controlled devices such as the air pump 22, air valve 23, fuel valve 44, and exhaust valve 46 described above. The ECU 100 functions as a power generation control unit, and is able to control the amount of anode gas supplied, the amount of cathode gas supplied, and the like by controlling the operation of the controlled devices according to the load (specifically, the current value) instructed to the fuel cell 10.

[0026] In the fuel cell system of this embodiment, the ECU 100 controls the operation of the controlled devices connected to the output side so that power corresponding to the power required by the load device 14 such as a traction motor is output. Specifically, a target current to be swept from the fuel cell 10 is set according to the load of the fuel cell 10, and the operation of the controlled devices is controlled so that the current swept from the fuel cell 10 is maintained at the target current. That is, in this specification, the load of the fuel cell 10 corresponds to the required power required of the fuel cell 10 by the load device 14 or the like, or the sweep current necessary to satisfy the required power.

[0027] A voltage detection unit 31, a current detection unit 32, a temperature detection unit 33, etc. are connected to the input side of the ECU 100. The voltage detection unit 31 is a voltmeter that detects the voltage output by the fuel cell 10. The voltage detection unit 31 is provided between both terminals of the fuel cell 10. The current detection unit 32 is an ammeter that detects the current extracted (i.e., swept) from the fuel cell 10. The current detection unit 32 is provided in the connection line between the fuel cell 10 and the inverter 11.

[0028] The temperature detection unit 33 is a thermometer that detects the temperature of the fuel cell 10. The temperature detection unit 33 is provided in a cooling water circuit (not shown) that cools the fuel cell 10, and detects the temperature of the cooling water immediately after it has passed through the fuel cell 10. The temperature of the cooling water detected by the temperature detection unit 33 corresponds to the temperature of the fuel cell 10.

[0029] Signals output from each sensor, such as the voltage detection unit 31, the current detection unit 32, and the temperature detection unit 33, are input to the ECU 100. The ECU 100 of this embodiment is configured to function as a cell deterioration detection unit that detects deterioration of the fuel cell 10. Specifically, the ECU 100 detects deterioration of the fuel cell 10 based on the relationship between the maximum current value (hereinafter referred to as the "previous maximum current value") detected by the current detection unit 32 within a predetermined time immediately before the fuel cell 10 performs predetermined medium-load power generation, and the voltage value (hereinafter referred to as the "execution voltage value") detected by the voltage detection unit 31 when the fuel cell 10 performs the predetermined medium-load power generation.

[0030] In this specification, power generation in the range of more than 0 and not more than 30% of the maximum load of the fuel cell 10 (i.e., the maximum current value commanded to the fuel cell 10) is referred to as low-load power generation, power generation in the range of 30% to 80% of the maximum load of the fuel cell 10 is referred to as medium-load power generation, and power generation of 80% or more of the maximum load of the fuel cell 10 is referred to as high-load power generation. In addition, a specified medium-load power generation refers to power generation at which a specified current value within the range of medium-load power generation is extracted.

[0031] Here, actual vehicle data measured by the inventors using a fuel cell system mounted on an actual vehicle is shown in FIG. 3 and FIG.

[0032] 3 shows data obtained by detecting multiple times (all times) the "immediately preceding maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation during a predetermined period (e.g., one month) when the fuel cell 10 is in an initial state, and the "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation. In this specification, the initial state of the fuel cell 10 refers to a certain period immediately after the fuel cell 10 is mounted on a vehicle. Moreover, the data detected multiple times actually refers to all data when a predetermined current value within the range of medium-load power generation is extracted during the predetermined period.

[0033] Figure 4 shows data obtained by detecting the "immediately preceding maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation and the "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation multiple times (all times) during a predetermined period (e.g., one month) that has elapsed a predetermined time (e.g., several years to several decades) since the period in which the data in Figure 3 was measured. In the following description, the period in which the data in Figure 3 was measured may be referred to as a first period, and the period in which the data in Figure 4 was measured may be referred to as a second period.

[0034] Here, the "last maximum current value" and the "runtime voltage value" used when acquiring the data in Figs. 3 and 4 will be described with reference to the graph in Fig. 5. In the graph in Fig. 5, the fuel cell 10 executes a predetermined medium-load power generation (i.e., power generation in which a predetermined current value within the range of medium-load power generation is extracted) in response to a request from the load device 14 after time t2. At this time, the ECU 100 detects the "last maximum current value", which is the maximum value of the current values ​​detected by the current detection unit 32 between time t1 and time t2, which is a predetermined time (e.g., 60 seconds) before time t2. In addition, the ECU 100 detects the "runtime voltage value", which is the voltage value when the fuel cell 10 executes the predetermined medium-load power generation after time t2. In Figs. 3 and 4, the data obtained in this manner is plotted with the "last maximum current value" on the horizontal axis and the "runtime voltage value" on the vertical axis.

[0035] In Figures 3 and 4, the more frequently the points indicating the "previous maximum current value" and the "runtime voltage value" when the fuel cell 10 performs a specified medium-load power generation during a specified period are placed in the same location, the larger the circle is and the darker it is shown in.

[0036] As shown in FIG. 3, in the first period when the fuel cell 10 is in the initial state, the "previous maximum current value" and the "runtime voltage value" have no tendency. The reason for this is considered as follows. That is, when the "previous maximum current value" is small, it means that low-load power generation was performed within a specified time immediately before the execution of a specified medium-load power generation (hereinafter, simply referred to as "within the previous specified time"). During low-load power generation, the flow rate of the cathode gas is small, so depending on the deterioration state of the fuel cell 10, the power generation state may be such that water is likely to accumulate in the MEA. However, since the MEA of the fuel cell 10 in the initial state has good drainage properties, the MEA is in a moderately wet state even when the flow rate of the cathode gas is small, such as during low-load power generation. Therefore, in the fuel cell 10 in the initial state, regardless of the previous maximum current value, when the specified medium-load power generation is performed, the MEA is in a moderately wet state, and the proton conductivity is good and the voltage value is relatively high, resulting in a good power generation state. Therefore, in the fuel cell 10 in the initial state, the "previous maximum current value" and the "runtime voltage value" have no tendency. In more detail, as shown in FIG. 3, the "runtime voltage value" varies depending on various operating conditions, excluding the influence of wetness or dryness of the MEA of the fuel cell 10, while the voltage value is relatively high.

[0037] In contrast, as shown in FIG. 4, in the second period after a predetermined time (e.g., several years to several decades) has passed since the initial state of the fuel cell 10, the smaller the "immediate maximum current value" is, the smaller the "runtime voltage value" tends to be. The reason for this is believed to be as follows. That is, in the second period after a predetermined time (e.g., several years to several decades) has passed since the initial state of the fuel cell 10, the drainage properties of the MEA have deteriorated compared to the initial state. The deterioration of the drainage properties of the MEA means that the MEA is less likely to dry or water is more likely to accumulate in the MEA compared to the initial state. Therefore, when the flow rate of the cathode gas is low, such as during low-load power generation, if the drainage properties of the MEA have deteriorated due to aging of the fuel cell 10, water generated by power generation is not drained from the MEA, and the MEA is likely to accumulate water (i.e., flooding state). Thus, in a fuel cell 10 that has deteriorated over time, the smaller the "previous maximum current value" is, the more likely it is that water will accumulate in the MEA. Therefore, when a specified medium-load power generation is subsequently performed, the water accumulated in the MEA will hinder the supply of cathode gas to the catalyst, resulting in a power generation state with a low "runtime voltage value."

[0038] On the other hand, if the "last maximum current value" is large, it means that high-load power generation was performed within the previous specified time. Since the flow rate of the cathode gas is large during high-load power generation, even if the drainage of the MEA has deteriorated due to aging of the fuel cell 10, the water generated during power generation is discharged from the MEA by the cathode gas, and the MEA is in a moderately wet state. Therefore, even if the fuel cell 10 has deteriorated with time, if the "last maximum current value" is large, the proton conductivity of the MEA will be good when a specified medium-load power generation is performed thereafter, and the "runtime voltage value" will be high, resulting in a good power generation state. Therefore, as the fuel cell 10 deteriorates with time from the initial state, the smaller the "last maximum current value" is, the smaller the "runtime voltage value" will gradually be seen. In FIG. 4, this tendency is indicated by the solid line A.

[0039] Therefore, the ECU 100 of this embodiment, as a cell deterioration detection unit, detects deterioration of the fuel cell 10 based on the relationship between the "previous maximum current value" and the "runtime voltage value". That is, as described above, as the fuel cell 10 deteriorates over time from the initial state, a gradual tendency emerges that the smaller the "previous maximum current value", the smaller the "runtime voltage value", and therefore it is possible to detect deterioration of the fuel cell 10.

[0040] Next, the deterioration determination process executed by the ECU 100 of this embodiment will be described with reference to the flowchart of FIG.

[0041] As shown in FIG. 6, in step S110, ECU 100 calculates and stores a maximum current value, which is the maximum value of the current values ​​detected by current detection unit 32, in a predetermined time (for example, 60 seconds) cycle.

[0042] Next, in step S120, the ECU 100 acquires data obtained by detecting a "previous maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation during a predetermined period (e.g., one month) when the fuel cell 10 is in the initial state, and an "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation multiple times. Then, based on the data, the relationship between the "previous maximum current value" and the "execution voltage value" is calculated and stored. Specifically, the ECU 100 calculates and stores data such as that shown in FIG. 3.

[0043] Next, in step S130, the ECU 100 acquires data on a fixed period basis, similar to step S120, that detects the "previous maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation during a predetermined period (e.g., one month) and the "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation multiple times. Then, based on the data, the relationship between the "previous maximum current value" and the "execution voltage value" is calculated and stored. Specifically, the ECU 100 calculates and stores data such as that shown in FIG. 4.

[0044] Next, in step S140, the ECU 100 compares the relationship between the "last maximum current value" and the "execution voltage value" stored in step S120 with the relationship between the "last maximum current value" and the "execution voltage value" stored in step S130. That is, the ECU 100 checks whether or not the data acquired in step S130 shows a tendency that the smaller the "last maximum current value" is, the smaller the "execution voltage value" is. Furthermore, the ECU 100 calculates and stores the tendency that the smaller the "last maximum current value" is, in the data acquired in step S130, as the slope of a graph as shown by the solid line A in FIG. 4. The slope of the graph can also be expressed as the rate of increase in the "execution voltage value" relative to the increase in the "last maximum current value".

[0045] Next, in step S150, the ECU 100 determines whether the slope of the graph calculated in step S140 is greater than a predetermined slope pre-stored in the ECU 100. Specifically, the ECU 100 determines whether the rate of increase of the "execution voltage value" relative to the increase of the "previous maximum current value" is greater than a predetermined threshold pre-stored in the ECU 100. The predetermined threshold is set by an experiment or the like and pre-stored in the ECU 100. If the slope of the graph calculated in step S140 is not greater than the predetermined slope pre-stored in the ECU 100 (i.e., NO in step S150), the ECU 100 returns the process to step S130. On the other hand, if the slope of the graph calculated in step S140 is greater than the predetermined slope pre-stored in the ECU 100 (i.e., YES in step S150), the ECU 100 advances the process to step S160.

[0046] In step S160, the ECU 100 determines that aging deterioration related to flooding has occurred in the fuel cell 10, and proceeds to step S170.

[0047] In step S170, the ECU 100 executes degradation recovery control of the fuel cell 10. In the degradation recovery control, for example, a process is executed to increase the air stoichiometric ratio according to the degree of degradation of the fuel cell 10. Specifically, in low load power generation or medium load power generation, the ECU 100 increases the flow rate of cathode gas required for power generation according to the degree of degradation of the fuel cell 10, thereby discharging water accumulated in the MEA and keeping the MEA appropriately moist.

[0048] The fuel cell system of the present embodiment described above has the following advantageous effects. That is, in the fuel cell system, the ECU 100, which serves as a cell deterioration detection unit, detects deterioration of the fuel cell 10 based on the relationship between the "immediate maximum current value" within a predetermined time period immediately prior to the fuel cell 10 generating power for a predetermined load, and the "runtime voltage value" when the fuel cell 10 generates power for that predetermined load. Therefore, this fuel cell system can accurately determine deterioration of the fuel cell 10 without detecting various operating states of the fuel cell 10 as in the determination device described in the above-mentioned Patent Document 1.

[0049] (1) In this embodiment, the ECU 100 uses, as the "power generation at a predetermined load" used to detect deterioration of the fuel cell 10, "power generation at which a predetermined current value is extracted within the range of medium load power generation." According to this, the inventors' intensive research has found that when the fuel cell 10 has deteriorated over time, the "runtime voltage value" during medium-load power generation is significantly affected by the "previous maximum current value". The reason for this is that when the fuel cell 10 has deteriorated over time, when the fuel cell 10 performs low-load power generation, water is likely to accumulate in the MEA (i.e., a flooded state), regardless of the power generation within the previous specified time, so the "runtime voltage value" is in a low power generation state. On the other hand, even when the fuel cell 10 has deteriorated over time, when the fuel cell 10 performs high-load power generation, water generated during power generation is discharged from the MEA by the cathode gas, regardless of the power generation within the previous specified time, so the "runtime voltage value" is in a high power generation state. On the other hand, when the fuel cell 10 has deteriorated over time, when the fuel cell 10 performs medium-load power generation, the wetness state of the MEA changes depending on the power generation load within the previous specified time, so the "runtime voltage value" is affected. In this way, the "runtime voltage value" during medium-load power generation is significantly affected by the "previous maximum current value". Therefore, in this embodiment, deterioration of the fuel cell 10 is detected based on the relationship between the "runtime voltage value" of the medium load power generation and the "previous maximum current value" within a predetermined period immediately preceding that. This allows the fuel cell system to accurately determine deterioration of the fuel cell 10.

[0050] (2) In this embodiment, the ECU 100 detects deterioration of the fuel cell 10 based on data obtained by detecting the "previous maximum current value" and the "runtime voltage value" multiple times when the fuel cell 10 generates power during a specified period. This makes it possible to see a trend that the smaller the "previous maximum current value" is, the smaller the "runtime voltage value" is, from the data obtained by detecting the "previous maximum current value" and the "runtime voltage value" multiple times when the fuel cell 10 generates power during a specified period. Therefore, deterioration of the fuel cell 10 can be accurately determined based on data detected multiple times during a specified period.

[0051] (3) In this embodiment, the ECU 100 detects deterioration of the fuel cell 10 by comparing the "relationship between the 'last maximum current value' and the 'runtime voltage value' detected multiple times during a first period" with the "relationship between the 'last maximum current value' and the 'runtime voltage value' detected multiple times during a second period a predetermined time after the first period." According to this, by comparing data detected multiple times during the first period with data detected multiple times during the second period, it can be seen that a trend appears in which the smaller the "last maximum current value" is, the smaller the "runtime voltage value," and that this trend gradually becomes stronger. Therefore, by comparing data detected multiple times during the first period with data detected multiple times during the second period, deterioration of the fuel cell 10 can be accurately determined.

[0052] (4) In this embodiment, the first period is a predetermined period in the initial state of the fuel cell 10. According to this, in the initial state of the fuel cell 10, there is no trend between the "previous maximum current value" and the "runtime voltage value", but as the fuel cell 10 deteriorates over time, a tendency gradually emerges in which the smaller the "previous maximum current value", the smaller the "runtime voltage value". Therefore, by comparing data detected multiple times during the first period when the fuel cell 10 is in the initial state with data detected multiple times during a second period a predetermined time has elapsed since the initial state, it is possible to accurately determine the deterioration of the fuel cell 10.

[0053] Second embodiment The second embodiment will be described with reference to Figure 7 and Figures 8A to 8C. The second embodiment is different from the first embodiment in that the processing performed after the deterioration of the fuel cell 10 is determined is changed, and the rest of the second embodiment is the same as the first embodiment, so only the differences from the first embodiment will be described.

[0054] First, in the description of the second embodiment, the conditions under which flooding occurs in the aged fuel cell 10 will be described with reference to the graph of FIG.

[0055] The vertical axis of the graph in FIG. 7 indicates the deterioration state of the fuel cell 10. The deterioration state of the fuel cell 10 correlates with the magnitude of the slope of the graph in the relationship between the "previous maximum current value" and the "runtime voltage value" shown by the solid line A in FIG. 4. The slope of the graph shown by the solid line A in FIG. 4 can also be expressed as the rate of increase in the "runtime voltage value" relative to the increase in the "previous maximum current value". The horizontal axis of the graph in FIG. 7 indicates the load threshold at which flooding may occur when the fuel cell 10 continues to generate power for a predetermined period of time.

[0056] As shown in the graph of FIG. 7, the load threshold at which the fuel cell 10 may cause flooding increases as the degree of deterioration of the fuel cell 10 progresses. For example, as in D1 and F1 of FIG. 7, when the degree of deterioration of the fuel cell 10 is low, flooding may occur when the fuel cell 10 continues low-load power generation for a predetermined period of time. In contrast, when the degree of deterioration of the fuel cell 10 is high, as in D2 and F2 of FIG. 7, flooding may occur not only when the fuel cell 10 continues low-load power generation for a predetermined period of time, but also when the fuel cell 10 continues medium-load power generation for a predetermined period of time. That is, the condition at which flooding occurs in the fuel cell 10 (i.e., the load threshold) changes depending on the deterioration state of the fuel cell 10. For this reason, in the deterioration determination process executed by the ECU 100 of the second embodiment described below, the process after the deterioration determination of the fuel cell 10 is changed from the deterioration determination process described in the first embodiment.

[0057] The deterioration determination process executed by the ECU 100 of the second embodiment will be described below with reference to the flowcharts of FIGS. 8A to 8C.

[0058] As shown in FIG. 8A, in step S210, ECU 100 calculates and stores a maximum current value that is the maximum value of the current values ​​detected by current detection unit 32 in a predetermined time (for example, 60 seconds) cycle.

[0059] Next, in step S220, the ECU 100 acquires data obtained by detecting a "previous maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation during a predetermined period (e.g., one month) when the fuel cell 10 is in the initial state, and an "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation multiple times. Then, based on the data, the relationship between the "previous maximum current value" and the "execution voltage value" is calculated and stored. Specifically, the ECU 100 calculates and stores data such as that shown in FIG. 3.

[0060] Next, in step S230, the ECU 100 acquires data obtained by detecting a "previous maximum current value" within a predetermined time (e.g., 60 seconds) immediately before the fuel cell 10 performs a predetermined medium-load power generation during a predetermined period (e.g., one month) in fixed time units, and an "execution voltage value" when the fuel cell 10 performs the predetermined medium-load power generation, in the same manner as in step S220. Then, based on the data, the relationship between the "previous maximum current value" and the "execution voltage value" is calculated and stored. Specifically, the ECU 100 calculates and stores data such as that shown in FIG. 4.

[0061] Next, in step S240, the ECU 100 compares the relationship between the "last maximum current value" and the "execution voltage value" stored in step S220 with the relationship between the "last maximum current value" and the "execution voltage value" stored in step S230. That is, the ECU 100 checks whether or not the data acquired in step S230 shows a tendency that the smaller the "last maximum current value" is, the smaller the "execution voltage value" is. Furthermore, the ECU 100 calculates and stores the tendency that the smaller the "last maximum current value" is, in the data acquired in S230, as the slope of a graph as shown by the solid line A in FIG. 4. The slope of the graph can also be expressed as the rate of increase in the "execution voltage value" relative to the increase in the "last maximum current value".

[0062] Next, in step S250, ECU 100 determines whether or not the slope of the graph calculated in step S240 is greater than a predetermined slope pre-stored in ECU 100. Specifically, ECU 100 determines whether or not the rate of increase of the "execution voltage value" relative to the increase of the "previous maximum current value" is greater than a predetermined threshold pre-stored in ECU 100. Note that the predetermined threshold is set by experiment or the like and pre-stored in ECU 100. When ECU 100 determines that the slope of the graph calculated in step S240 is greater than the predetermined slope pre-stored in ECU 100 (i.e., the determination in step S250 is YES), the process proceeds to step S260.

[0063] As shown in FIG. 8B, in step S260, the ECU 100 determines that aging deterioration related to flooding has occurred in the fuel cell 10, and proceeds to step S270.

[0064] In step S270, when at least one of low load power generation and medium load power generation is executed, ECU 100 measures the duration of this operation, and proceeds to step S280.

[0065] In step S280, the ECU 100 determines whether the duration measured in step S270 is equal to or longer than a predetermined time pre-stored in the ECU 100. This is because, in a fuel cell 10 determined to have deteriorated over time, if at least one of low-load power generation and medium-load power generation is performed continuously for a predetermined time or longer, the MEA may enter a flooded state. If the duration measured in step S270 is equal to or longer than the predetermined time, the ECU 100 advances the process to step S290.

[0066] In step S290, ECU 100 temporarily performs high-load power generation. In high-load power generation, the flow rate of the cathode gas is high, so that the water accumulated in the MEA can be discharged by the cathode gas, and the MEA can be changed from a flooded state to a moderately wet state.

[0067] On the other hand, in the judgment process described in step S250 above, if ECU 100 determines that the slope of the graph calculated in step S240 is not greater than the predetermined slope pre-stored in ECU 100 (i.e., NO in step S250), the process returns to step S230 and proceeds with the process from step S300 onwards.

[0068] As shown in FIG. 8C, in step S300, the ECU 100 determines that aging deterioration related to flooding has not occurred in the fuel cell 10, and proceeds to step S310.

[0069] In step S310, when low-load power generation is executed, ECU 100 measures the duration of this operation, and proceeds to step S320.

[0070] In step S320, the ECU 100 determines whether the duration measured in step S310 is equal to or longer than a predetermined time pre-stored in the ECU 100. This is because even if the fuel cell 10 is determined to have no aged deterioration, if the fuel cell 10 continues to perform low-load power generation for a predetermined time or longer, the flow rate of the cathode gas is low and the MEA may enter a flooded state. When the duration measured in step S320 is equal to or longer than the predetermined time, the ECU 100 advances the process to step S330.

[0071] In step S330, the ECU 100 temporarily performs high-load power generation. In high-load power generation, the flow rate of the cathode gas is high, so that the water accumulated in the MEA can be discharged by the cathode gas, and the MEA can be changed from a flooded state to a moderately wet state.

[0072] The fuel cell system of the second embodiment described above has the following advantages. In other words, in the second embodiment, when the ECU 100 determines that the fuel cell 10 is in a degraded state, if at least one of low-load power generation and medium-load power generation continues for a predetermined period of time or more, the ECU 100 temporarily performs high-load power generation. Also, even if the ECU 100 determines that the fuel cell 10 is not in a degraded state, if low-load power generation continues for a predetermined period of time or more, the ECU 100 temporarily performs high-load power generation. According to this, when the fuel cell 10 is in a degraded state, the MEA may become flooded even if not only low-load power generation but also medium-load power generation continues for a predetermined period of time or more. In that case, the ECU 100 as the power generation control unit temporarily performs high-load power generation, thereby discharging the water accumulated in the MEA by using the cathode gas, and the MEA can be kept in a moderately wet state. Even if the fuel cell 10 is not in a degraded state, the MEA may enter a flooded state if low-load power generation continues for a predetermined time or more. In that case, the ECU 100 as the power generation control unit temporarily performs high-load power generation to discharge the water accumulated in the MEA by using the cathode gas, and the MEA can be kept in a moderately wet state. In other words, the power generation control unit can switch the load threshold, which is the criterion for determining whether the MEA will enter a flooded state, depending on whether the fuel cell 10 is in a degraded state, and execute a process to eliminate the flooded state.

[0073] (Other embodiments) In each of the above embodiments, all data when a predetermined current value within the range of low-load power generation during a predetermined period is taken into consideration as data detected multiple times when the fuel cell 10 generates low-load power during a predetermined period, but this is not limited to this. For example, since there is variation in voltage depending on the operating state even during the day, by drawing an approximation line (linear) taking into account the voltage frequency, deterioration can be accurately determined regardless of the operating state. Also, for example, by extracting only data in which a predetermined current value continues for a predetermined time (e.g., 1 second or more) during medium-load power generation, deterioration can be accurately determined regardless of the operating state.

[0074] The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope of the claims. Moreover, the above-described embodiments are not unrelated to each other, and can be appropriately combined, except when the combination is clearly impossible. Moreover, in each of the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except when they are specifically stated to be essential or when they are clearly considered to be essential in principle. Moreover, in each of the above-described embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiments are mentioned, they are not limited to the specific numbers, except when they are specifically stated to be essential or when they are clearly limited to a specific number in principle. Moreover, in each of the above-described embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when they are specifically stated to be essential or when they are clearly limited to a specific shape, positional relationship, etc. in principle.

[0075] The control unit and the method according to the present invention may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method according to the present invention may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method according to the present invention may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0076] 10 fuel cell 31 Voltage detection section 32 Current detection section 100 Electronic control device (battery deterioration detection unit)

Claims

1. In a fuel cell system, a fuel cell (10) including a plurality of stacked fuel cell units (C) each configured to generate electricity by supplying a fuel gas as an anode gas and an oxidant gas as a cathode gas to one side and the other side of a membrane electrode assembly including an electrolyte membrane, respectively; A voltage detection unit (31) for detecting a voltage value output by the fuel cell; a current detection unit (32) for detecting a current value taken from the fuel cell; A fuel cell system comprising: a cell deterioration detection unit (100) that detects deterioration of the fuel cell based on the relationship between a previous maximum current value, which is the maximum value among the current values ​​detected by the current detection unit within a specified time immediately before the fuel cell generates a specified load, and an execution voltage value, which is the voltage value detected by the voltage detection unit when the fuel cell generates the specified load.

2. 2. The fuel cell system according to claim 1, wherein the power generation at the predetermined load is power generation at which a predetermined current value is extracted within a range of medium load power generation.

3. 3. The fuel cell system according to claim 1, wherein the battery deterioration detection unit detects deterioration of the fuel cell based on data obtained by detecting the most recent maximum current value and the runtime voltage value multiple times when the fuel cell generates power during a predetermined period.

4. 4. A fuel cell system as described in any one of claims 1 to 3, wherein the battery deterioration detection unit detects deterioration of the fuel cell by comparing "the relationship between the immediately preceding maximum current value and the runtime voltage value detected multiple times during a first period" with "the relationship between the immediately preceding maximum current value and the runtime voltage value detected multiple times during a second period a predetermined time after the first period."

5. 5. The fuel cell system according to claim 4, wherein the first period is a predetermined period in an initial state of the fuel cell.

6. When the fuel cell is determined not to be in a deteriorated state by the cell deterioration detection unit, if low-load power generation continues for a predetermined period of time or more, high-load power generation is temporarily performed; A fuel cell system as described in any one of claims 1 to 5, wherein when the battery deterioration detection unit determines that the fuel cell is in a deteriorated state, high-load power generation is temporarily performed if at least one of low-load power generation and medium-load power generation continues for a predetermined period of time or more.

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