fuel cell system

Abstract

To perform an appropriate recovery operation in accordance with a degradation mode occurring in a fuel cell stack.SOLUTION: A fuel cell system 1 is configured by including a fuel cell stack FCS configured by laminating fuel cells C1 to Cn and a control unit 3 that controls a power generation state of the fuel cell stack FCS. When the control unit 3 causes the fuel cell stack FCS to generate power, the control unit 3 determines whether a cathode-side toxification is occurring in which an organic solvent adheres to each cathode-side catalyst of fuel cells C1 to Cn on the basis of a relationship of a plurality of voltage acquisition results relating to voltages V1 to Vn on each of the fuel cells C1 to Cn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system including a fuel cell stack configured by stacking a plurality of fuel cells. [Background technology]

[0002] There is a fuel cell system that determines whether a deterioration mode occurring in a fuel cell stack is a deterioration mode in which organic solvent gas adheres to a cathode-side catalyst, thereby reducing the performance of the fuel cell stack (hereinafter referred to as cathode-side poisoning).Related technology is disclosed in Patent Document 1.

[0003] Incidentally, there are two types of degradation modes: a reversible degradation mode in which the fuel cell stack can be restored from a degraded state to its original normal state by performing a recovery operation, and an irreversible degradation mode in which the fuel cell stack cannot be restored from a degraded state to its original normal state. In addition to the cathode-side poisoning mentioned above, the reversible degradation mode also includes a degradation mode (hereinafter referred to as water clogging) in which the performance of the fuel cell stack is reduced due to water accumulation in the fuel gas and oxidant gas supply paths (particularly the oxygen gas supply path in solid polymer fuel cells).

[0004] One possible recovery operation to deal with cathode-side poisoning is to operate the fuel cell stack to generate electricity so that the current density of the current output from the fuel cell stack is relatively high (hereinafter referred to as high current density operation). By operating at a high current density, the organic solvent adhering to the cathode catalyst is washed away by the actively produced water, and the fuel cell stack is restored from its deteriorated state to its original normal state.

[0005] On the other hand, a possible recovery operation to deal with water blockages is, for example, to increase the pressure of the fuel gas in the fuel cell stack, and then repeatedly stop the supply of fuel gas to the fuel cell stack until the pressure of the fuel gas in the fuel cell stack drops to a predetermined pressure (hereinafter referred to as pulsating operation). By performing pulsating operation, water accumulated in the fuel cell stack is discharged outside the fuel cell stack, and the state of the fuel cell stack is restored from a deteriorated state to its original normal state. Related technology is described in Patent Document 2.

[0006] As described above, the recovery operation differs depending on the type of reversible degradation mode. Therefore, although the fuel cell system can determine whether the degradation mode occurring in the fuel cell stack is due to cathode-side poisoning, it cannot determine whether the degradation mode is due to water clogging, and therefore it is unable to perform an appropriate recovery operation according to the type of reversible degradation mode, which raises concerns that it may be difficult to maintain the performance of the fuel cell stack. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-22458 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-63712 Summary of the Invention [Problem to be solved by the invention]

[0008] An object according to one aspect of the present invention is to provide a fuel cell system capable of performing an appropriate recovery operation in accordance with a deterioration mode occurring in a fuel cell stack. [Means for solving the problem]

[0009] A fuel cell system according to one aspect of the present invention includes a fuel cell stack configured by stacking a plurality of fuel cells, and a control unit that controls the power generation state of the fuel cell stack.

[0010] When the control unit is causing the fuel cell stack to generate power, it determines whether the degradation mode occurring in the fuel cell stack is cathode-side poisoning based on the relationship between multiple voltage acquisition results regarding the voltages of the multiple fuel cell cells.

[0011] For example, when cathode-side poisoning occurs in a fuel cell stack, the voltage of each fuel cell decreases compared to when degradation does not occur in the fuel cell stack. Therefore, when the voltage difference between the maximum and minimum voltages of each fuel cell is relatively small, it can be determined that cathode-side poisoning may have occurred. In other words, based on the voltages of each fuel cell, it can be determined whether the degradation mode occurring in the fuel cell stack is cathode-side poisoning. As a result, when cathode-side poisoning occurs, recovery operations can be performed to address the cathode-side poisoning.

[0012] The control unit may also be configured to determine that the degradation mode occurring in the fuel cell stack is the cathode-side poisoning or irreversible degradation mode when the minimum voltage among the voltages of each of the fuel cell cells is equal to or less than a first threshold value and when the voltage difference between the maximum voltage and the minimum voltage among the voltages of each of the fuel cell cells is equal to or less than a second threshold value.

[0013] The control unit may also be configured to determine that the degradation mode occurring in the fuel cell stack is the cathode side poisoning or the irreversible degradation mode, and after performing a recovery operation corresponding to the cathode side poisoning, determine that the irreversible degradation mode has occurred in at least one of the fuel cell cells if the minimum voltage among the voltages of each of the fuel cell cells is equal to or less than a third threshold value.

[0014] The control unit may also determine that the degradation mode occurring in the fuel cell stack is the cathode-side poisoning or the irreversible degradation mode, and after performing a recovery operation corresponding to the cathode-side poisoning, determine that recovery from the cathode-side poisoning has occurred if the minimum voltage among the voltages of each of the fuel cell cells is greater than the third threshold value, and set the third threshold value to a value greater than the first threshold value.

[0015] This makes it difficult for the minimum voltage to become larger than the third threshold value, so that in cases where the increase in the voltage of the fuel cell due to a single recovery operation corresponding to cathode-side poisoning is relatively small, the recovery operation corresponding to the cathode-side poisoning can be performed repeatedly, thereby allowing the fuel cell stack to be sufficiently recovered. [Effects of the Invention]

[0016] According to the present invention, it is possible to carry out an appropriate recovery operation in accordance with the deterioration mode occurring in the fuel cell stack. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram illustrating an example of a fuel cell system according to an embodiment. [Figure 2] 10 is a flowchart showing an example of a deterioration determination operation. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0019] FIG. 1 is a diagram illustrating an example of a fuel cell system according to an embodiment.

[0020] 1 is mounted on a vehicle Ve, such as an industrial vehicle such as a forklift, an automobile, etc. The vehicle Ve is equipped with a load Lo, such as an inverter that drives a traction motor, and power is supplied from the fuel cell system 1 to the load Lo.

[0021] The fuel cell system 1 also includes a fuel cell stack FCS, a voltage detection unit VD, a fuel tank T, a main stop valve SV, an injector INJ, a gas-liquid separator GLS, a circulation pump HP, an exhaust drain valve EDV, a diluter DIL, an air compressor ACP, an air pressure regulating valve ARV, and an air shutoff valve ASV.

[0022] The fuel cell system 1 also includes a radiator R, a fan F, a water pump WP, an intercooler IC, a high-voltage side DCDC converter CNVH, a low-voltage side DCDC converter CNVL, a high-voltage side power storage device BH, a low-voltage side power storage device BL, a current sensor Sif, a voltage sensor Svf, a memory unit 2, and a control unit 3.

[0023] The fuel cell stack FCS is a fuel cell constructed by stacking multiple fuel cell cells C (fuel cell cells C1 to Cn), and generates electricity through an electrochemical reaction between the hydrogen contained in the fuel gas (such as hydrogen gas) and the oxygen contained in the oxidant gas (such as air).

[0024] Each of the fuel cells C1 to Cn is constructed by stacking separators in which flow paths for the fuel gas and oxidant gas are formed, an anode catalyst for a hydrogen oxidation reaction in which electrons are released from hydrogen contained in the fuel gas, a cathode catalyst for a redox reaction in which electrons are received by oxygen contained in the oxidant gas, and an electrolyte membrane provided between the anode catalyst and the cathode catalyst. Furthermore, the fuel cells C1 to Cn are all fastened together with fastening members to form a fuel cell stack FCS.

[0025] For example, when an oxidant gas is supplied to the fuel cell stack FCS, if the oxidant gas (air) supplied to the fuel cell stack FCS together with the oxidant gas contains organic solvent gas, the organic solvent will adhere to the cathode catalyst of each of the fuel cell cells C1 to Cn. For example, if a relatively large amount of organic solvent gas is supplied to the fuel cell stack FCS because a paint spray is used near the fuel cell system 1, the amount of organic solvent adhering to the cathode catalyst of each of the fuel cell cells C1 to Cn will increase. As a result, the oxidation-reduction reaction rate in each of the fuel cell cells C1 to Cn will become slower than normal, and the voltage of each of the fuel cell cells C1 to Cn will drop below normal (cathode-side poisoning). The high current density operation described above is one example of a recovery operation to deal with "cathode-side poisoning."

[0026] Furthermore, water generated by the combination of hydrogen ions and oxygen ions may accumulate in the flow paths of the fuel cell. This phenomenon of water accumulation in the flow paths is likely to occur in some fuel cell cells, resulting in a decrease in the amount of fuel gas and oxidant gas supplied to the fuel cell cells C corresponding to those separators. As a result, the hydrogen oxidation reaction rate and redox reaction rate in some fuel cell cells C become slower than normal, causing the voltage of some fuel cell cells C to drop below normal (water blockage). One example of a recovery operation to deal with "water blockage" is to increase the pressure of the fuel gas in the fuel cell stack FCS or increase the amount of oxidant gas supplied to the fuel cell stack FCS (hereinafter referred to as "pressurized air blowing operation"). By performing the pressurized air blowing operation, the water accumulated in the fuel cell stack FCS is discharged outside the fuel cell stack FCS, restoring the fuel cell stack FCS from its deteriorated state to its original normal state. Another example of a recovery operation to deal with "water blockage" is the pulsating operation described above.

[0027] In this way, "cathode side poisoning" and "water clogging" correspond to "reversible deterioration mode" and can be resolved by carrying out recovery operations according to the "reversible deterioration mode."

[0028] As with the "reversible degradation mode," there are multiple types of "irreversible degradation modes" that can occur in the fuel cell stack FCS. For example, in the "irreversible degradation modes" 1) to 4) below, the voltage of all or some of the fuel cell cells C that make up the fuel cell stack FCS drops below the normal voltage. Therefore, even if it is determined that degradation has occurred in the fuel cell stack FCS because the minimum voltage of each of the fuel cell cells C1 to Cn becomes a relatively low voltage, it is not possible to identify which of the "cathode-side poisoning," "water clogging," and "irreversible degradation mode" this degradation mode is. 1) Fluctuations in the potential of the fuel cell cause dissolution and redeposition of the cathode catalyst and anode catalyst, reducing the surface area of the cathode catalyst and anode catalyst, causing the voltage of fuel cell C to drop below normal (potential fluctuations). 2) The oxidation of the supporting carbon that holds the catalyst reduces the effective surface area of the catalyst, causing the voltage of the fuel cell C to drop below the normal voltage (carbon oxidation). 3) The resistance loss increases due to a decrease in the fastening load applied to all of the fuel cell units C1 to Cn, causing the voltage of the fuel cell unit C to drop below the normal voltage (lower fastening load). 4) Thinning or holes in the polymer membrane inside the fuel cell cause fuel gas to leak from the anode side to the cathode side, causing the voltage of fuel cell C to drop below normal (cross leakage).

[0029] The voltage detection unit VD detects the voltages V1 to Vn of the fuel cells C1 to Cn, respectively, and sends the detected voltages V1 to Vn to the control unit 3.

[0030] The fuel tank T is a storage container for fuel gas. The fuel gas stored in the fuel tank T is supplied to the fuel cell stack FCS via the main stop valve SV and the injector INJ.

[0031] The main stop valve SV is configured by an electromagnetic valve or the like, and supplies fuel gas to the injector INJ. The main stop valve SV is controlled by the control unit 3 to cut off the supply of fuel gas to the injector INJ.

[0032] The injector INJ adjusts the flow rate of the fuel gas so that the pressure of the fuel gas supplied to the fuel cell stack FCS is constant.

[0033] The gas-liquid separator GLS separates the fuel gas and liquid water discharged from the fuel cell stack FCS.

[0034] The circulation pump HP supplies the fuel gas separated by the gas-liquid separator GLS back to the fuel cell stack FCS.

[0035] The exhaust drain valve EDV sends the liquid water separated by the gas-liquid separator GLS to the diluter DIL. The liquid water sent to the diluter DIL accumulates in a tank inside the diluter DIL. In addition, the fuel gas and oxidant gas discharged from the fuel cell stack FCS join together in the diluter DIL and are discharged outside the fuel cell system 1.

[0036] The air compressor ACP compresses the oxidant gas present around the fuel cell system 1 and supplies it to the fuel cell stack FCS via the intercooler IC and the air shutoff valve ASV. The compression rate of the air compressor ACP is controlled by adjusting the opening of the air pressure regulating valve ARV provided downstream of the fuel cell stack FCS.

[0037] The intercooler IC exchanges heat between the oxidant gas, which has been heated by compression, and a refrigerant such as cooling water flowing through the intercooler IC.

[0038] The air shutoff valve ASV is controlled by the control unit 3 to shut off the supply of oxidant gas to the fuel cell stack FCS.

[0039] The air pressure regulating valve ARV adjusts the pressure and flow rate of the oxidant gas supplied to the fuel cell stack FCS.

[0040] The radiator R exchanges heat between the refrigerant, which has been heated by the heat generated by the fuel cell stack FCS, and the outside air.

[0041] Fan F increases the amount of heat dissipated by radiator R.

[0042] The water pump WP supplies the refrigerant cooled by the radiator R to the fuel cell stack FCS via the intercooler IC.

[0043] The high-voltage side DC-DC converter CNVH is connected downstream of the fuel cell stack FCS and converts the voltage Vfc (e.g., 90 [V]) output from the fuel cell stack FCS into a voltage Vch (e.g., 48 [V]). The power output from the high-voltage side DC-DC converter CNVH is supplied to the load Lo, the high-voltage side internal load LiH, and the high-voltage side power storage device BH. The high-voltage side internal load LiH is the circulation pump HP, the air compressor ACP, and the water pump WP.

[0044] The high-voltage side power storage device BH is configured by a lithium ion capacitor or the like, and is connected between the high-voltage side DC-DC converter CNVH and the load Lo.

[0045] The low-voltage side DCDC converter CNVL is connected after the high-voltage side DCDC converter CNVH and the high-voltage side battery BH, and converts the voltage Vch output from the high-voltage side DCDC converter CNVH or the voltage Vbh of the high-voltage side battery BH to a voltage Vbl (for example, 12 V). The power output from the low-voltage side DCDC converter CNVL is supplied to the low-voltage side internal load LiL and the low-voltage side battery BL. The low-voltage side internal load LiL includes the main stop valve SV, the fan F, the air shutoff valve ASV, and the air pressure regulating valve ARV.

[0046] The low-voltage side power storage device BL is configured by a lead battery or the like, and is connected to the rear stage of the low-voltage side DC-DC converter CNVL.

[0047] When the supply power corresponding to the difference between the power output from the high-voltage side DC-DC converter CNVH and the total value of the power supplied to the high-voltage side internal load LiH and the low-voltage side internal load LiL is greater than the power required by the load Lo, the power corresponding to the required power is supplied to the load Lo, and the remaining power is supplied to the high-voltage side power storage device BH and the low-voltage side power storage device BL. When power is supplied from the high-voltage side DC-DC converter CNVH to the high-voltage side power storage device BH, the high-voltage side power storage device BH is charged, and the charge amount CH of the high-voltage side power storage device BH increases. Furthermore, when the supply power corresponding to the difference between the power output from the high-voltage side DC-DC converter CNVH and the total value of the power supplied to the high-voltage side internal load LiH and the low-voltage side internal load LiL is less than the power required by the load Lo, the supply power is supplied to the load Lo, and the shortfall in power is supplied from the high-voltage side power storage device BH to the load Lo. When power is supplied from the high-voltage side power storage device BH to the load Lo, the high-voltage side power storage device BH is discharged, and the charge amount CH of the high-voltage side power storage device BH decreases. Note that the charge amount CH may be the charge rate [%] of the high-voltage side power storage device BH (the ratio of the remaining capacity to the full charge capacity of the high-voltage side power storage device BH), the open-circuit voltage [V] of the high-voltage side power storage device BH when no current is flowing through the high-voltage side power storage device BH, the closed-circuit voltage [V] of the high-voltage side power storage device BH when current is flowing through the high-voltage side power storage device BH, or the integrated value [Ah] of the current flowing through the high-voltage side power storage device BH, etc.

[0048] When the power output from the low-voltage side DCDC converter CNVL is greater than the power consumed by the low-voltage side internal load LiL, the remaining power output from the low-voltage side DCDC converter CNVL other than the power consumed by the low-voltage side internal load LiL is supplied to the low-voltage side storage device BL. When power is supplied to the low-voltage side storage device BL from the high-voltage side DCDC converter CNVH or the low-voltage side DCDC converter CNVL, the low-voltage side storage device BL is charged and the charge amount CL of the low-voltage side storage device BL increases. Also, when the power output from the low-voltage side DCDC converter CNVL is less than the power consumed by the low-voltage side internal load LiL, the power output from the low-voltage side DCDC converter CNVL is supplied to the low-voltage side internal load LiL, and the shortfall in power is supplied from the low-voltage side storage device BL to the low-voltage side internal load LiL. When power is supplied from the low-voltage side storage device BL to the low-voltage side internal load LiL, the low-voltage side storage device BL is discharged, and the charge amount CL of the low-voltage side storage device BL decreases. Note that the charge amount CL may be the charge rate [%] of the low-voltage side storage device BL (the ratio of the remaining capacity to the full charge capacity of the low-voltage side storage device BL), the open circuit voltage [V] of the low-voltage side storage device BL when no current is flowing through the low-voltage side storage device BL, the closed circuit voltage [V] of the low-voltage side storage device BL when current is flowing through the low-voltage side storage device BL, or the integrated value [Ah] of the current flowing through the low-voltage side storage device BL, etc.

[0049] The current sensor Sif is configured with a shunt resistor, a Hall element, etc., and detects the current Ifc flowing from the fuel cell stack FCS to the high-voltage side DC-DC converter CNVH, and sends the detected current Ifc to the control unit 3.

[0050] The voltage sensor Svf is configured with a voltage dividing resistor and the like, detects the voltage Vfc of the fuel cell stack FCS, and sends the detected voltage Vfc to the control unit 3.

[0051] The storage unit 2 is configured by a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

[0052] The control unit 3 is configured by a microcomputer and the like.

[0053] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 changes the target power generation power Pt in stages according to the charge amount CH of the high-voltage side power storage device BH.

[0054] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 controls the operation of the high-voltage side internal load LiH and the low-voltage side internal load LiL so that the power generated by the fuel cell stack FCS (the product of the current Ifc and the voltage Vfc) follows the target power generation Pt. For example, when the fuel cell stack FCS is generating power, the control unit 3 controls the operation of the high-voltage side internal load LiH and the low-voltage side internal load LiL by PI (Proportional-Integral) control so that the difference between the power generated by the fuel cell stack FCS and the target power generation Pt becomes zero.

[0055] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 executes a degradation determination operation at the degradation determination timing. That is, when executing the degradation determination operation, the control unit 3 determines whether degradation ("cathode-side poisoning," "water clogging," or "irreversible degradation mode") has occurred in the fuel cell stack FCS based on the voltages of the fuel cell units C1 to Cn. Furthermore, when the control unit 3 determines that degradation has occurred in the fuel cell stack FCS, it identifies the type of degradation mode occurring in the fuel cell stack FCS based on the voltages of the fuel cell units C1 to Cn.

[0056] For example, if the degradation mode occurring in the fuel cell stack FCS is "cathode-side poisoning," the voltages V1 to Vn will each be lower than when degradation does not occur in the fuel cell stack FCS. Furthermore, if the degradation mode occurring in the fuel cell stack FCS is "water clogging," some of the voltages V1 to Vn will be lower than when degradation does not occur in the fuel cell stack FCS. Furthermore, if the degradation mode occurring in the fuel cell stack FCS is "irreversible degradation mode," the voltages V1 to Vn will each be lower, or some of the voltages V1 to Vn will be lower, than when degradation does not occur in the fuel cell stack FCS. Therefore, if the voltage difference ΔV between the maximum voltage Vmax and the minimum voltage Vmin of the voltages V1 to Vn is relatively small, it can be determined that "cathode-side poisoning" or "irreversible degradation mode" has occurred. Furthermore, if the voltage difference ΔV is relatively large, it can be determined that "water clogging" or "irreversible degradation mode" has occurred. Furthermore, if it is determined that "cathode-side poisoning" or "irreversible degradation mode" has occurred, and a recovery operation corresponding to the "cathode-side poisoning" is performed and the degradation is resolved, it can be determined that "cathode-side poisoning" has occurred. Furthermore, if it is determined that "water clogging" or "irreversible degradation mode" has occurred, and a recovery operation corresponding to the "water clogging" is performed and the degradation is resolved, it can be determined that "water clogging" has occurred. Furthermore, if it is determined that "cathode-side poisoning" or "irreversible degradation mode" has occurred, and a recovery operation corresponding to the "cathode-side poisoning" is performed and the degradation is not resolved, it can be determined that "irreversible degradation mode" has occurred. Furthermore, if it is determined that "water clogging" or "irreversible degradation mode" has occurred, and a recovery operation corresponding to the "water clogging" is performed and the degradation is not resolved, it can be determined that "irreversible degradation mode" has occurred. In other words, based on the voltages V1 to Vn of the respective fuel cell units C1 to Cn, the degradation mode occurring in the fuel cell stack FCS can be divided into "cathode-side poisoning," "water clogging," or "irreversible degradation mode."

[0057] Fig. 2 is a flowchart showing an example of a deterioration determination operation. The control unit 3 executes the deterioration determination operation shown in Fig. 2 when the timing for determining deterioration arrives while the fuel cell stack FCS is generating electricity. For example, the timing for determining deterioration may be repeated at regular time intervals while the fuel cell stack FCS is generating electricity, or may be constantly performed while the fuel cell stack FCS is generating electricity. Alternatively, the timing may be when the fuel cell stack FCS starts or ends generating electricity.

[0058] First, the control unit 3 acquires the voltages V1 to Vn detected by the voltage detection unit VD (step S101).

[0059] Next, if the minimum voltage Vmin of the voltages V1 to Vn acquired in step S101 is a negative voltage, or if the minimum voltage Vmin is greater than the degradation determination threshold Vde (first threshold), i.e., if it is determined that the fuel cell stack FCS is not degraded (step S102: No), the control unit 3 terminates the degradation determination operation for the current degradation determination timing and continues power generation by the fuel cell stack FCS. For example, the degradation determination threshold Vde is set to the maximum positive voltage among the voltages V1 to Vn when degradation (cathode-side poisoning, water clogging, or irreversible degradation mode) occurs in the fuel cell stack FCS. For example, if the voltages V1 to Vn when the fuel cell stack FCS is in a normal state are set to around +0.8 [V], the degradation determination threshold Vde is set to +0.5 [V]. In this way, if the maximum positive voltage among the voltages V1 to Vn when degradation occurs in the fuel cell stack FCS is set to the degradation determination threshold Vde, it can be determined that the fuel cell stack FCS is not degraded when the minimum voltage Vmin is greater than the degradation determination threshold Vde. Furthermore, when the minimum voltage Vmin is a negative voltage, it can be determined that an abnormality other than degradation of the fuel cell stack FCS has occurred, such as a failure of the voltage detection unit VD. When an abnormality other than degradation of the fuel cell stack FCS has occurred, power generation by the fuel cell stack FCS may be stopped depending on the type of abnormality.

[0060] On the other hand, if the control unit 3 determines that the minimum voltage Vmin is equal to or greater than zero and equal to or less than the degradation determination threshold Vde, i.e., that degradation has occurred in the fuel cell stack FCS (step S102: Yes), it determines whether the voltage difference ΔV between the maximum voltage Vmax and the minimum voltage Vmin among the voltages V1 to Vn acquired in step S101 is equal to or less than a degradation mode specifying threshold ΔVth (second threshold) (step S103). For example, the degradation mode specifying threshold ΔVth is set to the maximum value of the voltage difference ΔV when "cathode-side poisoning" has occurred in the fuel cell stack FCS.

[0061] Next, if the voltage difference ΔV is equal to or less than the degradation mode specifying threshold ΔVth (step S103: Yes), the control unit 3 determines that the degradation mode occurring in the fuel cell stack FCS is "cathode side poisoning" or "irreversible degradation mode" (step S104), performs a recovery operation corresponding to "cathode side poisoning" (step S105), and then proceeds to the processing of step S106. As described above, when "cathode side poisoning" occurs in the fuel cell stack FCS, the voltages V1 to Vn each become lower than the normal voltage. Furthermore, when the fuel cell stack FCS is in the "irreversible degradation mode," there is a risk that the voltages V1 to Vn each become lower than the normal voltage. Therefore, if the voltage difference ΔV is equal to or less than the degradation mode specifying threshold ΔVth, it is possible to determine that the degradation mode occurring in the fuel cell stack FCS is "cathode side poisoning" or "irreversible degradation mode."

[0062] On the other hand, if the voltage difference ΔV is greater than the degradation mode identifying threshold ΔVth (step S103: No), the control unit 3 determines that the degradation mode occurring in the fuel cell stack FCS is "water clogging" or "irreversible degradation mode" (step S107), and after performing recovery operations corresponding to the "water clogging" (step S108), proceeds to the processing of step S109. As described above, when "water clogging" occurs in the fuel cell stack FCS, some of the voltages V1 to Vn will drop. Furthermore, when the fuel cell stack FCS is in the "irreversible degradation mode," some of the voltages V1 to Vn may also drop. Therefore, if the voltage difference ΔV is greater than the degradation mode identifying threshold ΔVth, it can be determined that the degradation mode occurring in the fuel cell stack FCS is "water clogging" or "irreversible degradation mode."

[0063] Furthermore, after performing a recovery operation (for example, the above-mentioned high current density operation) corresponding to "cathode-side poisoning" (step S105), the control unit 3 acquires the voltages V1 to Vn detected by the voltage detection unit VD (step S106), and determines whether the minimum voltage Vmin among the voltages V1 to Vn acquired in step S106 is greater than a recovery determination threshold Vr1 (third threshold) (step S110). For example, the recovery determination threshold Vr1 is set to the maximum positive voltage among the voltages V1 to Vn when "cathode-side poisoning" has occurred in the fuel cell stack FCS. For example, if the voltages V1 to Vn when the fuel cell stack FCS is in a normal state are around +0.8 [V], the recovery determination threshold Vr1 is set to +0.5 [V], the same as the deterioration determination threshold Vde. In this way, if the recovery determination threshold Vr1 is the maximum positive voltage among the voltages V1 to Vn when "cathode-side poisoning" occurs in the fuel cell stack FCS, it can be determined that the "cathode-side poisoning" that occurred in the fuel cell stack FCS has been eliminated when the minimum voltage Vmin is greater than the recovery determination threshold Vr1. The recovery determination threshold Vr1 may also be set to a value greater than the deterioration determination threshold Vde. In this way, if the recovery determination threshold Vr1 is set to a value greater than the deterioration determination threshold Vde, it is possible to make it less likely that the minimum voltage Vmin will exceed the recovery determination threshold Vr1 in step S110. This allows the recovery operation corresponding to the cathode-side poisoning to be performed repeatedly, even if the increase in voltage of the fuel cell C due to a single recovery operation corresponding to the cathode-side poisoning is relatively small, and therefore the fuel cell stack FCS can be sufficiently recovered.

[0064] Next, if the control unit 3 determines that the minimum voltage Vmin is greater than the recovery determination threshold Vr1 (step S110: Yes), it determines that the state of the fuel cell stack FCS, which had experienced "cathode-side poisoning," has recovered to a normal state (step S111), terminates the degradation determination operation for the current degradation determination timing, and continues power generation by the fuel cell stack FCS. In other words, if the control unit 3 determines that "cathode-side poisoning" or an "irreversible degradation mode" has occurred in the fuel cell stack FCS, it performs a recovery operation corresponding to "cathode-side poisoning," and if, as a result, the state of the fuel cell stack FCS recovers from the deteriorated state to its original normal state, it determines that the degradation mode that had occurred in the fuel cell stack FCS was "cathode-side poisoning," and terminates the degradation determination operation for the current degradation determination timing.

[0065] On the other hand, if the minimum voltage Vmin is equal to or less than the recovery determination threshold Vr1 (step S110: No), the control unit 3 determines that the deterioration mode occurring in the fuel cell stack FCS is the "irreversible deterioration mode" (step S112).

[0066] Furthermore, after performing a recovery operation (e.g., the pressurized air blowing operation) corresponding to the "water clogging" (step S108), the control unit 3 acquires the voltages V1 to Vn detected by the voltage detection unit VD (step S109) and determines whether the minimum voltage Vmin among the voltages V1 to Vn acquired in step S109 is greater than a recovery determination threshold Vr2 (step S113). For example, the recovery determination threshold Vr2 is set to the maximum positive voltage among the voltages V1 to Vn when "water clogging" has occurred in the fuel cell stack FCS. For example, if the voltages V1 to Vn when the fuel cell stack FCS is in a normal state are set to around +0.8 [V], the recovery determination threshold Vr2 is set to +0.5 [V], similar to the deterioration determination threshold Vde. In this way, if the maximum positive voltage among the voltages V1 to Vn when "water clogging" has occurred in the fuel cell stack FCS is set to the recovery determination threshold Vr2, it can be determined that the "water clogging" that has occurred in the fuel cell stack FCS has been resolved when the minimum voltage Vmin is greater than the recovery determination threshold Vr2. Furthermore, the recovery determination threshold Vr2 may be set to a value greater than the degradation determination threshold Vde. In this way, when the recovery determination threshold Vr2 is set to a value greater than the degradation determination threshold Vde, it is possible to suppress erroneous determination in step S113 due to erroneous detection of the voltages V1 to Vn, thereby improving the accuracy of the recovery determination.

[0067] Next, if the control unit 3 determines that the minimum voltage Vmin is greater than the recovery determination threshold Vr2 (step S113: Yes), it determines that the state of the fuel cell stack FCS, which had experienced "water clogging," has recovered to a normal state (step S114), and after terminating the degradation determination operation for the current degradation determination timing, continues power generation by the fuel cell stack FCS. In other words, if the control unit 3 determines that "water clogging" or an "irreversible degradation mode" has occurred in the fuel cell stack FCS, it performs a recovery operation corresponding to the "water clogging," and as a result, if the state of the fuel cell stack FCS recovers from the deteriorated state to its original normal state, it determines that the degradation mode that had occurred in the fuel cell stack FCS was "water clogging," and terminates the degradation determination operation for the current degradation determination timing.

[0068] On the other hand, if the minimum voltage Vmin is equal to or less than the recovery determination threshold Vr2 (step S113: No), the control unit 3 determines that the deterioration mode occurring in the fuel cell stack FCS is the "irreversible deterioration mode" (step S112).

[0069] Furthermore, after determining that the degradation mode occurring in the fuel cell stack FCS is the "irreversible degradation mode" (step S112), the control unit 3 determines whether the average voltage Vave of the voltages V1 to Vn acquired in step S106 or step S109 is smaller than the unusable determination threshold Vd (step S115). For example, the unusable determination threshold Vd is set to the average voltage Vave when the fuel cell stack FCS is in the "irreversible degradation mode," in which the voltages of the individual fuel cell units C1 to Cn are lower than their normal voltages. For example, if the voltages V1 to Vn when the fuel cell stack FCS is in a normal state are +0.8 to +1.0 [V], the unusable determination threshold Vd is set to +0.6 [V].

[0070] Next, if the average voltage Vave is equal to or lower than the unusable determination threshold Vd (step S115: Yes), the control unit 3 determines that the fuel cell stack FCS cannot be used because an "irreversible degradation mode" has occurred in each of the fuel cell cells C1 to Cn, stops power generation by the fuel cell stack FCS (step S116), and ends the degradation determination operation for this degradation determination timing.

[0071] On the other hand, if the average voltage Vave is greater than the unusable determination threshold Vd (step S113: No), the control unit 3 determines that the fuel cell C is in a normal state and therefore the fuel cell stack FCS can be used (step S117), and after completing the deterioration determination operation at this deterioration determination timing, continues power generation by the fuel cell stack FCS.

[0072] The control unit 3 may be configured to proceed to the processing of step S104 if all the deviations corresponding to the voltages V1 to Vn respectively (the difference between the average or median of the voltages V1 to Vn and one of the voltages V1 to Vn) are equal to or less than the degradation mode identifying threshold ΔVth in step S103, and to proceed to the processing of step S107 if all the deviations corresponding to the voltages V1 to Vn respectively are not equal to or less than the degradation mode identifying threshold ΔVth in step S103. In other words, the index for determining whether the degradation mode occurring in the fuel cell stack FCS is cathode-side poisoning is not particularly limited, and the control unit 3 may be configured to determine whether the degradation mode occurring in the fuel cell stack FCS is cathode-side poisoning based on the relationship between a plurality of voltage acquisition results related to the voltages V1 to Vn of the fuel cell units C1 to Cn when the fuel cell stack FCS is generating electricity.

[0073] 2, steps S106 to S117 may be omitted. In this configuration, when the voltage difference ΔV between the maximum voltage Vmax and the minimum voltage Vmin of the voltages V1 to Vn of each of the fuel cell cells C1 to Cn is equal to or less than the degradation mode specific threshold ΔVth, it can be determined that "cathode-side poisoning" or "irreversible degradation mode" has occurred. In other words, when the voltage difference ΔV is relatively small, it can be determined that "cathode-side poisoning" has occurred. As a result, when "cathode-side poisoning" has occurred, a recovery operation corresponding to "cathode-side poisoning" can be performed.

[0074] 2, steps S115 to S117 may be omitted, and power generation by the fuel cell stack FCS may be stopped after it is determined that the degradation mode occurring in the fuel cell stack FCS is the "irreversible degradation mode" (step S112). In this configuration, the life of the fuel cell system 1 can be extended by replacing the defective part of the fuel cell stack FCS that is the cause of the "irreversible degradation mode."

[0075] According to the fuel cell system 1 of the above embodiment, the degradation mode occurring in the fuel cell stack FCS can be classified into "cathode-side poisoning," "water clogging," or "irreversible degradation mode" based on the voltages V1 to Vn of the fuel cell units C1 to Cn, respectively. This allows appropriate recovery operations to be performed according to the degradation mode, and the performance of the fuel cell stack FCS can be maintained.

[0076] Furthermore, according to the fuel cell system 1 of the above embodiment, since it is configured to proactively perform recovery operations for the "reversible degradation mode", the state of the fuel cell stack FCS can be quickly returned from a degraded state to its original normal state, compared to when the "reversible degradation mode" is naturally resolved by normal power generation of the fuel cell stack FCS.

[0077] The present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0078] 1. Fuel cell system 2 Storage section 3. Control Unit Vehicle Lo load FCS fuel cell stack T Fuel Tank SV Main stop valve INJ injector GLS gas-liquid separator HP Circulation Pump EDV Exhaust Drain Valve DIL Diluter ACP Air Compressor ARV Air Pressure Regulating Valve ASV Air Shutoff Valve R radiator F Fan WP water pump IC intercooler CNVH High Voltage Side DCDC Converter CNVL Low voltage side DC / DC converter BH High-voltage side storage device BL Low voltage side storage device Sif current sensor SVF voltage sensor

Claims

1. a fuel cell stack formed by stacking a plurality of fuel cell units; a control unit that controls the power generation state of the fuel cell stack; Equipped with When the minimum voltage among the voltages of the fuel cell cells is equal to or less than a first threshold value and the voltage difference between the maximum voltage and the minimum voltage among the voltages of the fuel cell cells is equal to or less than a second threshold value, the control unit determines that the degradation mode occurring in the fuel cell stack is cathode-side poisoning or irreversible degradation mode. A fuel cell system characterized by:

2. 2. The fuel cell system according to claim 1, The control unit determines that the degradation mode occurring in the fuel cell stack is the cathode-side poisoning or the irreversible degradation mode, and after performing a recovery operation corresponding to the cathode-side poisoning, determines that the irreversible degradation mode has occurred in at least one of the fuel cell cells if the minimum voltage of each of the fuel cell cells is equal to or less than a third threshold value. A fuel cell system characterized by:

3. 3. The fuel cell system according to claim 2, the control unit determines that the degradation mode occurring in the fuel cell stack is the cathode-side poisoning or the irreversible degradation mode, and after performing a recovery operation corresponding to the cathode-side poisoning, determines that recovery from the cathode-side poisoning has been achieved if the minimum voltage among the voltages of the individual fuel cell units is greater than the third threshold value; The third threshold is greater than the first threshold. A fuel cell system characterized by:

Images