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. An impedance detection section 34 detects an impedance value of the fuel battery 10 when a predetermined high frequency wave is applied to the fuel battery 10. A voltage detection section 31 detects a voltage value output by 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 an impedance value at the time of the fuel battery 10 performing predetermined low load power generation and a voltage value at this time.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 can improve the accuracy of determining performance degradation of a fuel cell. [Means for solving the problem]

[0007] In order to achieve the above object, claim 1 and 3 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; an impedance detection unit (34) that detects an impedance value of the fuel cell when a predetermined high frequency is applied to the fuel cell; a voltage detection unit (31) that detects a voltage value output by the fuel cell; The fuel cell includes a cell degradation detection section (100) that detects degradation of the fuel cell based on the relationship between the impedance value when the fuel cell is generating power at a predetermined low load and the voltage value at that time. Furthermore, in the invention of claim 1, the battery deterioration detection unit detects deterioration of the fuel cell by comparing "data obtained by detecting multiple times the impedance value and the voltage value at that time when the fuel cell performs a specified low-load power generation during a first period" with "data obtained by detecting multiple times the impedance value and the voltage value at that time when the fuel cell performs a specified low-load power generation during a second period a specified time after the first period." In the invention of claim 3, the battery degradation detection unit determines that the fuel cell is in a degraded state when the "median value of the average of impedance values ​​detected multiple times when the fuel cell performs a specified low-load power generation during a second period a specified time after the first period" is smaller than the "median value of the average of impedance values ​​detected multiple times when the fuel cell performs a specified low-load power generation during a first period in the initial state of the fuel cell."

[0008] According to the inventors' research, the impedance value of a fuel cell when a certain high frequency (e.g., high frequency of 200 Hz or more) is applied to the fuel cell correlates with the wetness or dryness of the MEA. Specifically, a low impedance value indicates a wet MEA, and a high impedance value indicates a drier MEA.

[0009] When a fuel cell generates electricity at a low load, the flow rate of the cathode gas is low and water generated in the MEA due to power generation is difficult to discharge, so depending on the deterioration state of the MEA of the fuel cell, the power generation state may be such that water is likely to accumulate in the MEA. However, the drainage of the MEA is good in the initial state. Therefore, when a fuel cell in the initial state generates electricity at a predetermined low load, when the impedance value is low, the MEA is in a moderately wet state and has good proton conductivity, resulting in a good power generation state with a high voltage value. And, as the impedance value increases depending on various operating conditions of the fuel cell, the MEA gradually becomes drier, and the proton conductivity gradually decreases, resulting in a gradually lower voltage value. In this way, a fuel cell in the initial state has a strong tendency that when the impedance value is low, the voltage value is high, and as the impedance value increases, the voltage value is lower.

[0010] In contrast, as a fuel cell ages, the drainage properties of the MEA gradually deteriorate. Therefore, when an aged fuel cell generates electricity at a specified low load, if the impedance value is low, water is likely to accumulate in the MEA (i.e., a flooded state), preventing the supply of cathode gas to the catalyst and resulting in a power generation state with a low voltage value. In addition, since the MEA becomes difficult to dry, the impedance value rarely exhibits a high value. Therefore, as the fuel cell ages, the tendency seen in an initial fuel cell (i.e., the tendency that the higher the impedance value, the lower the voltage value) gradually becomes weaker.

[0011] Therefore, in the invention according to claim 1, deterioration of the fuel cell is detected based on the relationship between the impedance value when the fuel cell generates a predetermined low-load power and the voltage value at that time. That is, as described above, as the fuel cell deteriorates over time from its initial state, when the fuel cell generates a predetermined low-load power, the tendency for the voltage value to be lower as the impedance value is higher gradually decreases, 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.

[0012] In this specification, low-load power generation refers to power generation at a load in the range of more than 0 and not more than 30% of the maximum load of the fuel cell (i.e., the maximum current value commanded to the fuel cell). Also, a specified low-load power generation refers to power generation at which a specified current value within the range of low-load power generation is extracted.

[0013] The predetermined high frequency is equal to or higher than 200 Hz, which makes it possible to detect an impedance value that correlates with the wetness or dryness of the MEA.

[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 impedance value and the voltage value at that time multiple times when the fuel cell generates a predetermined low load power during a predetermined period in the initial state of the fuel cell. [Figure 4]This data is obtained by detecting the impedance value and the voltage value at that time multiple times during a predetermined period of time after the fuel cell is in an initial state and the fuel cell is generating a predetermined low load power. [Diagram 5] This data shows impedance values ​​and voltage values ​​detected multiple times when the fuel cell performs a predetermined low-load power generation during a predetermined period that is a predetermined time after the predetermined period in FIG. [Figure 6] 4 is a flowchart of a deterioration determination process executed by an electronic control device provided in the fuel cell system according to the first embodiment. [Figure 7] 13 shows data obtained by detecting impedance values ​​and voltage values ​​multiple times when the fuel cell performs predetermined low-load power generation during a predetermined period in the initial state of the fuel cell in a fuel cell system according to a second embodiment. [Figure 8] This data is obtained by detecting the impedance value and the voltage value at that time multiple times during a predetermined period of time after the fuel cell is in an initial state and the fuel cell is generating a predetermined low load power. [Figure 9] 10 is a flowchart of a degradation determination process executed by an electronic control device included in a fuel cell system according to a second embodiment. [Figure 10] 1 is a graph showing the relationship between the temperature and impedance of a fuel cell. 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 5. 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, an impedance detection unit 34, 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] The impedance detection unit 34 is a device that detects the impedance of the fuel cell 10. The impedance detection unit 34 has an AC superposition unit 341 that superposes an AC signal of a predetermined frequency on the current swept from the fuel cell 10, and a calculation unit 342 that calculates the impedance from the current on which the AC signal is superposed. The impedance detection unit 34 of this embodiment detects the impedance value of the fuel cell 10 when a predetermined high frequency (e.g., a high frequency of 200 Hz or more) is applied to the fuel cell 10. The impedance value thus detected has a high correlation with the wetness or dryness of the MEA of the fuel cell 10. Specifically, a low impedance value indicates a wet state of the MEA, and a higher impedance value indicates a drier state of the MEA.

[0030] Signals output from each sensor, such as the voltage detection unit 31, current detection unit 32, temperature detection unit 33, and impedance detection unit 34, 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 impedance value when the fuel cell 10 generates a predetermined low load power and the voltage value at that time.

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

[0032] FIG. 3 shows data obtained by detecting impedance values ​​and voltage values ​​multiple times (all times) when the fuel cell 10 performs a predetermined low-load power generation during a predetermined period (e.g., one month) when the fuel cell 10 is in an initial state. 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. In this specification, low-load power generation refers to a load in the range of more than 0 and less than or equal to 30% of the maximum load of the fuel cell 10 (i.e., the maximum current value commanded to the fuel cell 10). In addition, predetermined low-load power generation refers to power generation at which a predetermined current value within the range of low-load power generation is extracted. In addition, the data detected multiple times actually refers to all data when a predetermined current value within the range of low-load power generation is extracted during the predetermined period.

[0033] FIG. 4 shows data obtained by detecting the impedance value and the voltage value at that time multiple times (all times) during a predetermined period (e.g., one month) after a predetermined time (e.g., several years to several decades) has elapsed since the period when the data in FIG. 3 was measured. FIG. 5 shows data obtained by detecting the impedance value and the voltage value at that time multiple times (all times) during a predetermined period (e.g., one month) after a predetermined time (e.g., several years to several decades) has elapsed since the period when the data in FIG. 4 was measured. In the following description, the period when the data in FIG. 3 was measured may be referred to as a first period, and the period when the data in FIG. 4 or FIG. 5 was measured may be referred to as a second period.

[0034] In Figures 3 to 5, the more frequently a point indicating the impedance value when the fuel cell 10 is generating a specified low load power during a specified period and the voltage value at that time are placed in the same location, the larger the circle is and the darker the color is.

[0035] As shown in FIG. 3, in the first period when the fuel cell 10 is in the initial state, when the impedance value is low, the voltage value is high, and the higher the impedance value is, the lower the voltage value is. The reason for this is considered as follows. That is, when the fuel cell 10 performs low-load power generation, the flow rate of the cathode gas is low and water generated in the MEA due to power generation is difficult to discharge, so depending on the deterioration state of the MEA of the fuel cell 10, the power generation state may be such that water is likely to accumulate in the MEA. However, the MEA drainage property is good in the initial state of the fuel cell 10. Therefore, when the fuel cell 10 performs a predetermined low-load power generation in the initial state, when the impedance value is low, the MEA is in a moderately wet state and has good proton conductivity, resulting in a good power generation state with a high voltage value. And, as the impedance value is higher due to various operating conditions of the fuel cell 10, the MEA gradually becomes drier, and the proton conductivity gradually decreases, resulting in a gradually lower voltage value. Therefore, in the initial state, the fuel cell 10 has a tendency to have a high voltage value when the impedance value is low, and a low voltage value as the impedance value is high. In Figure 3, this tendency is shown by the solid line A.

[0036] Next, as shown in FIG. 4, in a second period in which a predetermined time (e.g., several years to several decades) has passed since the fuel cell 10 was in the initial state, the drainage property of the MEA has deteriorated compared to the initial state. The deterioration of the drainage property of the MEA means that the MEA has become more difficult to dry or water has become more likely to accumulate in the MEA compared to the initial state. Therefore, when the fuel cell 10 performs a predetermined low-load power generation, when the impedance value shows a low value, the MEA is likely to be in a state where water has accumulated (i.e., a flooding state), and the supply of the cathode gas to the catalyst may be hindered, resulting in a power generation state with a low voltage value. In addition, since the MEA becomes more difficult to dry, the impedance value hardly shows a high value. Therefore, as the fuel cell 10 deteriorates over time, the tendency seen in the fuel cell 10 in the initial state (i.e., the tendency that the higher the impedance value is, the lower the voltage value) gradually becomes smaller. In FIG. 4, this tendency is indicated by a solid line B.

[0037] 5, in the third period, which is a predetermined time (e.g., several years to several decades) after the second period, the drainage performance of the MEA further deteriorates, so that the impedance value hardly shows a high value, and the tendency seen in the first and second periods (i.e., the tendency that the higher the impedance value, the lower the voltage value) is hardly seen.

[0038] 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 impedance value and the voltage value at the time when the fuel cell 10 generates a predetermined low load electricity. That is, as described above, as the fuel cell 10 deteriorates over time from the initial state, when the fuel cell 10 generates a predetermined low load electricity, the tendency for the voltage value to be lower as the impedance value is higher gradually decreases, making it possible to detect deterioration of the fuel cell 10.

[0039] Next, the deterioration determination process executed by the ECU 100 of this embodiment will be described with reference to the flowchart of FIG.

[0040] As shown in Fig. 6, in step S110, the ECU 100 obtains data on the impedance value and the voltage value at the time when the fuel cell 10 generates a predetermined low load power during a predetermined period when the fuel cell 10 is in an initial state, detected multiple times. Then, based on the data, the relationship between the impedance value and the voltage value is calculated and stored. Specifically, the ECU 100 calculates and stores the tendency that the higher the impedance value is, the lower the voltage value is, as the slope of a graph of the relationship between the impedance value and the voltage value as shown by the solid line A in Fig. 3.

[0041] Next, in step S120, the ECU 100 acquires data on the impedance value and the voltage value at the time when the fuel cell 10 performs a predetermined low-load power generation during a predetermined period of time, similar to step S110, detected multiple times. Then, based on the data, the relationship between the impedance value and the voltage value is calculated and stored. Specifically, the ECU 100 calculates and stores the tendency that the higher the impedance value is, the lower the voltage value is, as the slope of a graph of the relationship between the impedance value and the voltage value, as shown by the solid line B in FIG. 4.

[0042] Subsequently, in step S130, ECU 100 compares the slope of the graph showing the relationship between impedance values ​​and voltage values ​​stored in step S110 with the slope of the graph showing the relationship between impedance values ​​and voltage values ​​stored in step S120.

[0043] Next, in step S140, ECU 100 determines whether the slope of the graph of the relationship between the impedance value and the voltage value stored in step S120 is smaller than the slope of the graph of the relationship between the impedance value and the voltage value stored in step S110. If ECU 100 determines that the slope is not small (i.e., NO in step S140), it returns the process to step S120. On the other hand, if ECU 100 determines that the slope is small (i.e., YES in step S140), it proceeds to step S150.

[0044] In step S150, the ECU 100 determines that aging deterioration related to flooding has occurred in the fuel cell 10, and proceeds to step S160.

[0045] In step S160, 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, the ECU 100 increases the flow rate of the cathode gas required for low-load 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.

[0046] 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 impedance value when the fuel cell 10 generates a predetermined low load and the voltage value at that time. 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.

[0047] (1) In this embodiment, the ECU 100 detects the deterioration of the fuel cell 10 based on data obtained by detecting the impedance value and the voltage value at that time multiple times when the fuel cell 10 generates a predetermined low-load power during a predetermined period. This makes it possible to see a tendency that the higher the impedance value, the lower the voltage value, from data obtained by detecting the impedance value and the voltage value at that time multiple times when the fuel cell 10 generates a predetermined low-load power during a predetermined period. Therefore, it is possible to accurately determine the deterioration of the fuel cell 10 based on data detected multiple times during a predetermined period.

[0048] (2) In this embodiment, the ECU 100 detects the deterioration of the fuel cell 10 by comparing "data obtained by detecting the impedance value and the voltage value at the time when the fuel cell 10 generates a predetermined low load power during a first period" with "data obtained by detecting the impedance value and the voltage value at the time when the fuel cell 10 generates a predetermined low load power during a second period a predetermined time after the first period." According to this, by comparing the data detected multiple times during the first period with the data detected multiple times during the second period, it is possible to see a gradual change in the tendency that the higher the impedance value is, the lower the voltage value becomes. Therefore, by comparing the data detected multiple times during the first period with the data detected multiple times during the second period, it is possible to accurately determine the deterioration of the fuel cell 10.

[0049] (3) 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, the higher the impedance value, the greater the tendency for the voltage value to be lower, and this tendency gradually decreases as the fuel cell 10 deteriorates with time. 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 after the initial state, it is possible to accurately determine the deterioration of the fuel cell 10.

[0050] Second embodiment The second embodiment will be described with reference to Figures 7 to 9. The second embodiment is different from the first embodiment in that the method of determining deterioration of the fuel cell 10 is changed, and other aspects are similar to the first embodiment, so only the differences from the first embodiment will be described.

[0051] Figure 7 shows the same data as Figure 3, and Figure 8 shows the same data as Figure 5. However, in Figures 7 and 8, dashed lines C and D respectively show the median values ​​obtained by averaging the impedance values ​​detected multiple times when the fuel cell 10 performs a specified low-load power generation during a specified period.

[0052] As shown by dashed line C in Figure 7 and dashed line D in Figure 8, as the fuel cell 10 deteriorates over time from its initial state, the median impedance value averaged over multiple detections made when the fuel cell 10 is generating a specified low load electricity becomes gradually smaller.

[0053] Therefore, in the second embodiment, the ECU 100, as a cell deterioration detection unit, detects deterioration of the fuel cell 10 by comparing the median of impedance values ​​detected multiple times while the fuel cell 10 is in the initial state with the median of impedance values ​​detected multiple times during a predetermined time period after the initial state. That is, as described above, as the fuel cell 10 deteriorates over time from the initial state, the median of the average of the impedance values ​​detected multiple times when the fuel cell 10 performs a predetermined low-load power generation gradually becomes smaller, making it possible to detect deterioration of the fuel cell 10.

[0054] Next, the deterioration determination process executed by the ECU 100 of the second embodiment will be described with reference to the flowchart of FIG.

[0055] As shown in FIG. 9, in step S200, the ECU 100 detects the temperature of the fuel cell 10 based on the output signal from the temperature detection section 33.

[0056] Next, in step S210, the ECU 100 acquires data on impedance values ​​detected multiple times when the fuel cell 10 generates a predetermined low load power at a predetermined temperature during a predetermined period when the fuel cell 10 is in an initial state. Then, based on the data, the ECU 100 calculates and stores the median of the impedance values ​​detected multiple times. Specifically, as shown by the dashed line C in FIG. 7, the ECU 100 calculates and stores the median by averaging the impedance values ​​detected multiple times.

[0057] Next, in step S220, the ECU 100 acquires data on impedance values ​​detected multiple times during a given period when the fuel cell 10 generates a specified low-load power at the same temperature as in step S210. Then, based on the data, the ECU 100 calculates and stores the median of the impedance values ​​detected multiple times. Specifically, as shown by the dashed line D in FIG. 8, the ECU 100 calculates and stores the median by averaging the impedance values ​​detected multiple times.

[0058] Next, in step S230, ECU 100 compares the median value of the impedance values ​​stored in step S220 with the median value of the impedance values ​​stored in step S210.

[0059] Next, in step S240, ECU 100 determines whether or not the median value of the impedance values ​​stored in step S220 is smaller than the median value of the impedance values ​​stored in step S210. If the median value of the impedance values ​​stored in step S220 is not smaller than the median value of the impedance values ​​stored in step S210, ECU 100 returns the process to step S220. On the other hand, if the median value is smaller, ECU 100 advances the process to step S250.

[0060] In step S250, the ECU 100 determines that aging deterioration related to flooding has occurred in the fuel cell 10, and proceeds to step S260.

[0061] In step S260, 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, the ECU 100 increases the flow rate of the cathode gas required for low-load 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.

[0062] The fuel cell system of the second embodiment described above has the following advantageous effects: In other words, in the second embodiment, the ECU 100 determines that the fuel cell 10 is in a degraded state when the "median value of the average of the impedance values ​​detected multiple times when the fuel cell 10 performs a predetermined low-load power generation during a second period a predetermined time after the first period" is smaller than the "median value of the average of the impedance values ​​detected multiple times when the fuel cell 10 performs a predetermined low-load power generation during a first period when the fuel cell 10 is in an initial state." According to the inventor's research, as the fuel cell 10 deteriorates over time from its initial state, the median average of the impedance values ​​detected multiple times when the fuel cell 10 generates a specified low load power becomes smaller. Therefore, by comparing the median average of the impedance values ​​detected multiple times during a first period when the fuel cell 10 is in its initial state with the median average of the impedance values ​​detected multiple times during a second period a specified time after the initial state, it is possible to accurately determine the deterioration of the fuel cell 10.

[0063] Furthermore, the method for determining the deterioration of the fuel cell 10 described in the second embodiment does not use a voltage value as a determination parameter, so it is not affected by factors such as reversible voltage fluctuations and has high accuracy. In addition, since it is not affected by other factors, it is possible to make a determination even in a short period of time such as one day.

[0064] Incidentally, as shown in the graph of Fig. 10, the impedance value represents the wet / dry state of the MEA, and therefore the impedance value also changes depending on the temperature of the fuel cell 10. Therefore, in the above-described second embodiment, data obtained when the temperature of the fuel cell 10 is the same is extracted as data detected multiple times when the fuel cell 10 performs low-load power generation during a specified period. This makes it possible to improve the accuracy of deterioration determination.

[0065] (Other embodiments) In each of the above embodiments, the data detected multiple times when the fuel cell 10 is performing low-load power generation during a specified period is taken into consideration when a specified current value within the range of low-load power generation during the specified period, and in the first embodiment, the slope is calculated, and in the second embodiment, the median is calculated, but this is not limited to this.

[0066] For example, since voltage varies depending on the operating state even during the day, by drawing an approximation line (linear) taking into account the voltage frequency, deterioration can be determined with high accuracy regardless of the operating state. Also, for example, by extracting only data in which a certain current value continues for a certain time (for example, 1 second or more) during low-load power generation, deterioration can be determined with high accuracy regardless of the operating state.

[0067] Moreover, the accuracy of deterioration determination can also be improved by combining the deterioration determination process described in the first embodiment with the deterioration determination process described in the second embodiment.

[0068] In addition, in step S140 of the deterioration determination process described in the first embodiment, ECU 100 determines whether the slope of the graph showing the relationship between the impedance value and the voltage value stored in step S120 is smaller than the slope of the graph showing the relationship between the impedance value and the voltage value stored in step S110, but this is not limited to the above. For example, the ECU 100 may calculate the rate of decrease in the voltage value in response to an increase in the impedance value in steps S110 and S120, and determine that the fuel cell 10 is in a degraded state when the difference between the rate of decrease calculated in step S110 and the rate of decrease calculated in step S120 is greater than a predetermined threshold value.

[0069] 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.

[0070] 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]

[0071] 10 Fuel Cell 31 Voltage detection section 34 Impedance 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; an impedance detection unit (34) for detecting an impedance value of the fuel cell when a predetermined high frequency is applied to the fuel cell; A voltage detection unit (31) for detecting a voltage value output by the fuel cell; a cell deterioration detection unit (100) that detects deterioration of the fuel cell based on the relationship between the impedance value when the fuel cell is generating a predetermined low load power and the voltage value at that time, A fuel cell system in which the battery deterioration detection unit detects deterioration of the fuel cell by comparing "data obtained by detecting multiple times the impedance value and the voltage value at that time when the fuel cell performs a specified low-load power generation during a first period" with "data obtained by detecting multiple times the impedance value and the voltage value at that time when the fuel cell performs a specified low-load power generation during a second period that is a specified time after the first period."

2. A fuel cell system as described in claim 1, wherein the first period is a predetermined period in an initial state of the fuel cell.

3. A fuel cell system comprising: 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; an impedance detection unit (34) for detecting an impedance value of the fuel cell when a predetermined high frequency is applied to the fuel cell; A voltage detection unit (31) for detecting a voltage value output by the fuel cell; a cell deterioration detection unit (100) that detects deterioration of the fuel cell based on the relationship between the impedance value when the fuel cell is generating a predetermined low load power and the voltage value at that time, A fuel cell system in which the battery deterioration detection unit determines that the fuel cell is in a deteriorated state when the "median value obtained by averaging impedance values ​​detected multiple times when the fuel cell performs a specified low-load power generation during a second period a specified time after the first period" is smaller than the "median value obtained by averaging impedance values ​​detected multiple times when the fuel cell performs a specified low-load power generation during a first period in the initial state of the fuel cell."

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