Verification procedure for fuel cell stacks

Abstract

A verification procedure for a fuel cell stack (20) comprising a plurality of unit cells (24), the procedure comprising the following steps: (a) Operating a fuel cell system (10) comprising the fuel cell stack (20) and an anode gas circulation flow path (62) arranged between an anode gas discharge port (26) and an anode gas supply port (25) of the fuel cell stack (20) to circulate anode gas under a predetermined condition in which liquid water is accumulated, in order to accumulate liquid water in the anode gas circulation flow path (62); (b) Following step (a), cause the fuel cell system (10) to stop and wait until a predetermined restart condition is met; and (c) Restarting the fuel cell system (10) after step (b) to implement power generation by the fuel cell stack (20) and measuring a voltage of each unit cell (24) to detect a unit cell (24) that has a negative voltage, wherein the operation under the liquid water accumulation condition in step (a) comprises: a low-load operation in which the fuel cell system (10) is operated such that the fuel cell stack (20) generates a current that is lower than a nominal current of the fuel cell stack (20); and a non-power-generating operation, which is carried out after low-load operation, in which the power generation by the fuel cell stack (20) is stopped and the fuel cell system (10) is operated in such a way that circulation of the anode gas in the anode gas circulation flow path (62) continues.

Description

BACKGROUND

[0001] The present disclosure relates to a method for detecting a unit cell from a plurality of unit cells in a fuel cell stack, the anode gas inlet flow path of which is likely to be clogged or blocked by liquid water. STATE OF THE ART

[0002] An anode gas flow path for a unit cell in a fuel cell stack can become clogged or blocked by liquid water produced during power generation. A purging process is performed to prevent the anode gas flow path from becoming clogged by liquid water when a fuel cell system is to be shut down. A fuel cell system disclosed in JP 2014-197481A performs the purging process, with the anode gas acting as a purge gas to expel any liquid water remaining in an anode exhaust flow path from the unit cell. This prevents the anode exhaust flow path from becoming clogged.

[0003] The inventors discovered that there is a potential unit cell that is likely to become clogged with liquid water due to an excessively small diameter of an anode gas flow path, attributable to a manufacturing defect. Liquid water clogging is particularly likely in structures with a locally small anode gas flow path, such as an anode gas inlet flow path using a comb-shaped flow path structure. If the anode gas inlet flow path is clogged, a unit cell will experience anode gas deficiency and exhibit negative voltage. Consequently, the unit cell may degrade. Unfortunately, if the unit cells are individually inspected before the fuel cell stack is assembled, it is difficult to determine whether liquid water clogging occurs because the locally small anode gas flow path is extremely small.Therefore, a verification method for a fuel cell stack is desirable that enables the detection of a single cell whose anode gas inlet flow path is likely to become blocked. A verification method for a fuel cell stack is disclosed, for example, in JP 2007-149443 A. Furthermore, with regard to the prior art for fuel cells, reference is made to JP 2016-85898 A, US 2013 / 0130140A1, and DE 102013014978A1. SUMMARY

[0004] The present disclosure was made to solve the problems described above and can be implemented in the form of the following aspects.

[0005] (1) According to one aspect of the present disclosure, a verification procedure is provided for a fuel cell stack comprising a plurality of unit cells.The verification procedure comprises: (a) operating a fuel cell system comprising the fuel cell stack and an anode gas recirculation flow path connected between an anode gas discharge port and an anode gas supply port of the fuel cell stack to recirculate anode gas under a predetermined condition in which liquid water accumulates; (b) causing the fuel cell system to stop and wait until a predetermined restart condition is met; and (c) restarting the fuel cell system after step (b) to implement power generation by the fuel cell stack and measuring a voltage of each unit cell to detect a unit cell exhibiting a negative voltage.

[0006] In the verification procedure for a fuel cell stack according to this aspect, liquid water accumulates in the anode gas recirculation flow path due to operation under conditions where liquid water is collected. Therefore, at the time of restart, the liquid water in the anode gas recirculation flow path flows into an anode gas inlet flow path from each unit cell. A unit cell with an excessively small anode gas inlet flow path will become clogged by the liquid water. Consequently, a unit cell will experience anode gas deficiency while power generation continues and will exhibit a negative voltage. By detecting a fuel cell exhibiting the negative voltage, it is possible to detect a unit cell whose anode gas inlet flow path is likely clogged.During standby mode after operation under conditions where liquid water accumulates, generated water in each unit cell moves from one cathode side to one anode side. Therefore, the spatial volume of anode gas in the unit cell decreases, and the remaining amount of anode gas also decreases. In this configuration, an anode gas deficiency is likely to occur in the unit cell after restart. This facilitates the detection of the negative voltage, thus easily identifying a unit cell whose anode gas inlet flow path is likely blocked.

[0007] According to a first aspect of the invention, operation under the condition in which liquid water is accumulated comprises, in step (a): a low-load operation in which the fuel cell system is operated such that the fuel cell stack generates a current that is lower than a rated current of the fuel cell stack; and a non-power-generating operation, which is carried out after the low-load operation in which the power generation by the fuel cell stack is stopped and the fuel cell system is operated while the anode gas continues to circulate in the anode gas circulation flow path.

[0008] In the verification procedure for a fuel cell stack, reactive gas flows at a low rate due to low-load operation, making it less likely that the generated water will be discharged from the unit cells. Therefore, a large amount of liquid water remains in the unit cells. Furthermore, condensation occurs in the anode gas recirculation flow path due to the non-power-generating operation, causing liquid water to accumulate there.

[0009] (2) According to another aspect, low-load operation can be carried out in such a way that the temperature of the fuel cell stack rises to a predetermined temperature of a complete heating cycle due to the low-load operation, while the temperature of an anode gas circulating pump placed in the anode gas circulation flow path does not reach the temperature of a complete heating cycle.

[0010] During the testing procedure for a fuel cell stack, the temperature of the anode exhaust gas rises sufficiently, while that of the anode gas recirculation pump does not rise as much. This leads to a temperature difference that causes condensation in the anode gas recirculation pump, resulting in the accumulation of a large amount of liquid water.

[0011] (3) According to another aspect, the restart condition may include at least either a condition that is met when a predetermined standby period expires after the fuel cell system has been stopped, and / or a condition that is met when the temperature of the fuel cell stack falls to a predetermined standby end temperature.

[0012] In the verification procedure for a fuel cell stack according to this aspect, the water will move sufficiently from the cathode side to the anode side of the unit cell, resulting in a shorter verification time.

[0013] (4) According to another aspect, step (a) can be carried out to accumulate liquid water in an anode gas circulating pump arranged in the anode gas circulating flow path.

[0014] In the verification procedure for a fuel cell stack according to this aspect, the liquid water will accumulate in the anode gas recirculation pump, whereby the liquid water in the anode gas recirculation pump is supplied to the fuel cell stack along with the anode gas when the fuel cell system is restarted.

[0015] (5) According to another aspect, step (c) may include the supply of anode gas to the fuel cell stack before the fuel cell stack starts generating electricity in order to replace any gas remaining on one anode side of the unit cells with the anode gas.

[0016] In the verification procedure for a fuel cell stack according to this aspect, the anode gas exchange step causes the liquid water in the anode gas circulation flow path to flow into the anode gas inlet flow path of each unit cell.

[0017] A verification method for a fuel cell stack comprising a plurality of unit cells, according to a further aspect of the invention, comprises: (a) operating a fuel cell system comprising the fuel cell stack and an anode gas circulation flow path connected between an anode gas discharge port and an anode gas supply port of the fuel cell stack to circulate anode gas, under a predetermined condition in which liquid water accumulates, in order to accumulate liquid water in the anode gas circulation flow path; (b) causing, according to step (a), the fuel cell system to stop and wait until a predetermined restart condition is met;and (c) restarting the fuel cell system after step (b) to implement power generation by the fuel cell stack, and measuring a voltage of each unit cell to detect a unit cell that has a negative voltage, wherein step (c) includes supplying anode gas to the fuel cell stack before power generation by the fuel cell stack begins in order to replace any gas remaining on an anode side of the unit cells with the anode gas.

[0018] The present disclosure can be implemented in various other forms besides those described above. For example, the present disclosure can be implemented as a testing device for a fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a diagram representing a schematic configuration of a fuel cell system according to an embodiment of the present disclosure. Fig. Figure 2 is a diagram that shows an exemplary schematic configuration of an anode-side separator of unit cells. Fig. Figure 3 is a flowchart that represents a verification procedure for a fuel cell stack. Fig. Figure 4 is a flowchart that illustrates an example of an accumulation process of liquid water. Fig. Figure 5 is a diagram that provides an example of how the current generated by the fuel cell stack, the flow rate of supplied hydrogen, and the flow rate of circulating hydrogen change over time during a verification process for the fuel cell stack. Fig. Figure 6 is a diagram that illustrates an example of how an anode gas inlet flow path becomes clogged by liquid water. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0019] Fig. Figure 1 is a diagram depicting a schematic configuration of a fuel cell system 10 according to an embodiment of the present disclosure, which is equipped with a fuel cell stack 20, which is a test target. In the present embodiment, the fuel cell stack 20 is tested while simulating the operation of the fuel cell system as it actually occurs when installed in a vehicle to deliver power and serve as a power source for the vehicle. The fuel cell system 10 has a configuration similar to that of an on-board fuel cell system.The fuel cell system 10 comprises the fuel cell stack 20, an anode gas supply circulation system 50, a cathode gas supply / drainage system 30, a coolant circulation system 70, a controller 80, a DC / DC converter 90, a power control unit (hereinafter referred to as "PCU") 91 and a cell monitoring device 95.

[0020] The fuel cell stack 20 comprises an end plate 21, an insulating plate 22, a collector plate 23, a plurality of unit cells 24, a current collector plate 23, an insulating plate 22, and an end plate 21, stacked in this order. Each unit cell 24 comprises a membrane electrode assembly (not shown) and two separators that enclose the membrane electrode assembly on both its anode and cathode sides.

[0021] The anode gas supply circulation system 50 is controlled by the controller 80 such that it supplies anode gas to the fuel cell stack 20 and circulates the anode gas. In the Fig. In the example shown in Figure 1, hydrogen is used as the anode gas. The anode gas supply circulation system 50 comprises a gas tank 40, a shut-off valve 41, an anode gas supply pipe 60, a regulator 51, an injector 54, an anode gas return pipe 61, an anode gas circulation pump 55, a gas-liquid separator 56, a shut-off valve 57, and a gas / liquid drain pipe 58.

[0022] The gas tank 40 stores hydrogen gas at high pressure, such as several tens of MPa. The anode gas supply pipe 60 is connected between the gas tank 40 and an anode gas supply port 25 of the fuel cell stack 20 to supply hydrogen from the gas tank 40 to the fuel cell stack 20. The shut-off valve 41, the regulator 51, and the injector 54 are arranged on the anode gas supply pipe 60 in this order, starting from the side closer to the gas tank 40. The regulator 51 adjusts the hydrogen pressure. The injector 54 injects hydrogen, the pressure of which has been adjusted by the regulator 51, into the anode gas supply port 25 of the fuel cell stack 20.

[0023] The anode gas return pipe 61, through which the anode gas is returned, is connected to an anode gas discharge port 26 of the fuel cell stack 20 and to a downstream section 60d of the anode gas supply pipe 60. The gas-liquid separator 56 and the anode gas recirculation pump 55 are positioned in the anode gas return pipe 61 in this order, starting from the side closer to the anode gas discharge port 26 of the fuel cell stack 20. The gas-liquid separator 56 separates the gas and liquid discharged from the anode gas discharge port 26 of the fuel cell stack 20. The gas emitted from the anode gas discharge port 26 mainly comprises hydrogen that did not contribute to power generation, nitrogen that moved from a cathode side to an anode side through the unit cells 24, and water vapor that was generated by power generation.The liquid discharged from the anode gas discharge port 26 consists mainly of liquid water produced during power generation. The gas-liquid separator 56 separates, among other things, nitrogen and liquid water, and discharges the nitrogen and liquid water to the outside via the shut-off valve 57 and the gas / liquid discharge pipe 58. Hydrogen and water vapor remaining in the gas-liquid separator 56 are returned as anode gas by the anode gas recirculation pump 55 to the anode gas return pipe 61, in order to be supplied again to the fuel cell stack 20 via the downstream section 60d of the anode gas supply pipe 60.The anode gas return pipe 61, the downstream section 60d of the anode gas supply pipe 60, the gas-liquid separator 56 and the anode gas circulation pump 55 form an anode gas circulation flow path 62, which is connected between the anode gas discharge port 26 and the anode gas supply port 25 of the fuel cell stack 20, and circulates the anode gas.

[0024] The cathode gas supply / drainage system 30 is controlled by the controller 80 such that it supplies cathode gas to the fuel cell stack 20 and discharges it from it. In the Fig. In the example shown, air is used as the cathode gas. The cathode gas supply / drainage system 30 comprises a cathode gas supply pipe 32, a compressor 31, a three-way valve 33, a bypass pipe 38, a pressure regulating valve 36, and a cathode gas drain pipe 39.

[0025] The cathode gas supply pipe 32 is connected to the fuel cell stack 20 and supplies the fuel cell stack 20 with air drawn in from the outside. An outside temperature sensor 35, an air flow meter 34, the compressor 31, and the three-way valve 33 are located in the cathode gas supply pipe 32 in this order, counting from one air inlet side. The outside temperature sensor 35 measures the temperature of the incoming air. The air flow meter 34 measures the volume of air drawn in. The compressor 31 compresses the incoming air. The three-way valve 33 is connected to the bypass pipe 38 and adjusts the airflow rate to the fuel cell stack 20 and the bypass pipe 38. The bypass pipe 38 is connected to the cathode gas outlet pipe 39.

[0026] The cathode gas vent pipe 39 has an upstream end section connected to the fuel cell stack 20 and an intermediate section connected to the bypass pipe 38 and the gas / liquid vent pipe 58 of the anode gas supply recirculation system 50. The cathode gas vent pipe 39 discharges cathode gas expelled from the fuel cell stack 20, some of the air diverted to the bypass pipe 38, and nitrogen and liquid water discharged from the gas / liquid vent pipe 58. The cathode gas vent pipe 39 is equipped with the pressure regulating valve 36. The pressure regulating valve 36 is positioned closer to the fuel cell stack 20 than the section where the cathode gas vent pipe 39 and the bypass pipe 38 are connected. The pressure regulating valve 36 adjusts the pressure of the air supplied to the fuel cell stack 20.

[0027] The coolant circulation system 70 is cooled by the controller 80 to cool the fuel cell stack 20. The coolant circulation system 70 comprises a coolant supply pipe 74, a coolant drain pipe 73, a radiator 71, a bypass pipe 77, a three-way valve 75, and a coolant pump 72. Examples of coolants to be used include water, non-freezing water such as ethylene glycol, and air. The coolant pump 72 is located in the coolant supply pipe 74 and supplies the coolant to the fuel cell stack 20. The three-way valve 75 adjusts the flow rate of the coolant to the radiator 71 and the bypass pipe 77. The coolant drain pipe 73, located near a coolant outlet 27 of the fuel cell stack 20, is equipped with a coolant drain temperature sensor 76.The coolant drain temperature sensor 76 measures the temperature of the coolant flowing through the coolant outlet 27 of the fuel cell stack 20 to measure the temperature of the fuel cell stack 20 while the fuel cell system 10 is operating. When the fuel cell system 10 is not operating, the coolant does not circulate. Therefore, the temperature of the fuel cell stack 20 is estimated based on a reading obtained from the coolant drain temperature sensor 76 and a reading obtained from the outside temperature sensor 35 or an outside temperature sensor (not shown) for an air conditioning system inside the vehicle. This temperature relationship is stored on non-volatile memory (not shown) in the controller 80 as a map or lookup table.

[0028] The controller 80 is configured as a computer comprising a central processing unit (CPU) and non-volatile memory, and is specifically an electronic control unit (ECU). The controller 80 outputs a signal to control the starting and stopping of the fuel cell system 10. Upon receiving a power generation request, the controller 80 activates the components of the fuel cell system 10 to cause the fuel cell stack 20 to generate electricity. The controller 80 controls the cell monitoring device 95 to measure the cell voltage of each of the unit cells 24 in the fuel cell stack 20. A cell voltage value for each of the unit cells 24, measured by the cell monitoring device 95, is transmitted to a cell voltage notification unit 82 of the controller 80 for external output as a notification.

[0029] The DC-DC converter 90 is controlled by the controller 80 to increase the voltage output from the fuel cell stack 20 and supply the resulting voltage to the PCU 91. The PCU 91 incorporates an inverter and is controlled by the controller 80 to supply power to a load. During a later test of the fuel cell stack 20, the PCU 91 is controlled by the controller 80 to adjust the current generated by the fuel cell stack 20.

[0030] Fig. Figure 2 is a diagram showing a schematic configuration of an anode-side separator 100 of the unit cell 24 in the fuel cell stack 20 ( Fig. 1) shown from the side view of a membrane electrode arrangement. In Fig. 2 is an X-direction, a horizontal direction; a Z-direction, a vertically upward direction; and a Y-direction, a stacking direction of the unit cells 24. The separator 100 has an end section in a longitudinal direction provided with an anode gas inlet collector 110, a coolant outlet collector 160, and a cathode gas inlet collector 130, arranged in that order from top to bottom. The other end section of the separator 100 has a cathode gas outlet collector 140, a coolant inlet collector 150, and an anode gas outlet collector 120, arranged in that order from top to bottom. The anode gas inlet collecting opening 110 and the anode gas outlet collecting opening 120 are each connected to the anode gas supply opening 25 and the anode gas discharge opening 26 of the in Fig. 1 shown fuel cell stack 20 in connection.

[0031] The separator 100 has a central section in which an anode gas flow path 105 is formed in the form of a plurality of strips. In the Fig. In the example shown, the anode gas flow path 105 is a coiled flow path in which a plurality of unit flow paths 105p are arranged in coils in the form of equally spaced depressions. An anode gas inlet flow path 111 is formed between the anode gas flow path 105 and the anode gas inlet collecting port 110. An anode gas outlet flow path 121 is formed between the anode gas flow path 105 and the anode gas outlet collecting port 120. The anode gas inlet flow path 111 comprises a plurality of unit inlet flow paths 111p in the form of depressions arranged at equally spaced intervals in the Z-direction, thus forming a comb-like structure. Similarly, the anode gas outlet flow path 121 comprises a plurality of unit outlet flow paths 121p in the form of depressions arranged at equal intervals in the Z direction, thus forming a comb structure.It should be noted that the anode gas inlet flow path 111 and the anode gas outlet flow path 121 do not have to have the comb-shaped structure.

[0032] The hydrogen supplied to the anode gas inlet collector 110 flows through the anode gas inlet flow path 111 to enter the anode gas flow path 105. The hydrogen that has flowed into the anode gas flow path 105 then flows in a convoluted manner and passes through the anode gas outlet flow path 121 to reach the anode gas outlet collector 120.

[0033] Fig. Figure 3 is a flowchart representing a verification procedure for a fuel cell stack according to an embodiment of the present disclosure. This flow begins in a state in which the entire fuel cell system 10 has been stopped, with the fuel cell stack 20, which is a verification target, as shown in Figure 3. Fig. 1 shown was mounted. In step S210, the controller 80 uses the temperature readings from the coolant drain temperature sensor 76 ( Fig. 1) and the outside temperature sensor 35 ( Fig. 1) were obtained to estimate the temperature of the fuel cell stack 20.

[0034] In step S220, the controller 80 determines whether the temperature of the fuel cell stack 20, estimated in step S210, has fallen to or below a verification start temperature. The verification start temperature is a temperature at which the fuel cell stack 20 can be considered to be at a sufficiently low temperature; it can be set, for example, to between 20 °C and 40 °C inclusive. If the temperature of the fuel cell stack 20 has fallen to or below the verification start temperature before start-up, the liquid water will readily accumulate in a liquid water accumulation process described later in step S320. If the fuel cell stack 20 has fallen to or below the verification start temperature, the temperature of other components (for example, the anode gas recirculation pump 55) of the fuel cell system 10 is expected to be less than or equal to the verification start temperature.Nevertheless, the determination condition in step S220 may further include a condition that is met if the temperature of the anode gas recirculation pump 55 has fallen to less than or equal to the verification start temperature. If step S220 determines that the temperature of the fuel cell stack 20 has not fallen to or below the verification start temperature, the process returns to step S210 and the temperature estimation continues. If step S220 determines that the temperature of the fuel cell stack 20 has fallen to or below the verification start temperature, the process proceeds to step S310. Note that steps S210 and S220 can be omitted.

[0035] In step S310, the controller 80 starts the fuel cell system 10. In step S320, the controller 80 operates the fuel cell system 10 under a condition in which liquid water accumulates, so that the liquid water accumulates in the anode gas circulation flow path 62 ( Fig. 1).

[0036] Fig. Figure 4 is a flowchart that shows an example of a liquid water accumulation process in step S320, which is in Fig. Figure 3 illustrates this. In step S322, the controller 80 performs low-load operation. "Low-load operation" refers to the operation of the fuel cell system 10 in which the fuel cell stack 20 generates an electric current that is lower than the rated current of the fuel cell stack 20. For example, an electric current between 2% and inclusive of 15% of the rated current is preferably generated by the fuel cell stack 20 in low-load operation. The fuel cell stack 20, whose operation has been started in this low-load manner, results in a low flow rate of the anode gas and the cathode gas due to the low load. This prevents the water generated in the unit cell 24 from being carried out and causes a large quantity of the generated water to remain in the unit cell 24.Low-load operation also serves as a preheating phase to increase the temperature of the fuel cell stack 20. In particular, the anode gas temperature gradually rises during low-load operation. As will be described later, low-load operation preferably ends before the temperature in the anode gas circulation flow path 62 (especially in the anode gas recirculation pump 55) rises significantly. Preferably, the anode gas supply circulation system 50 and the cathode gas supply / drain system 30 are operated during low-load operation such that a stoichiometric ratio of anode gas and cathode gas is set to a value within a suitable range (for example, between 1.20 and inclusive of 1.30). This “stoichiometric ratio” is a ratio of an actual reaction gas flow rate to a reaction gas flow rate theoretically required for power generation.

[0037] In step S324, the controller 80 determines whether low-load operation has ended. A low-load operation end condition can be met when the temperature of the fuel cell stack 20 reaches, for example, a predefined temperature of a completed heating cycle. For example, the temperature of a completed heating cycle is set to between 55 °C and 60 °C inclusive. When low-load operation is complete, the temperature of the fuel cell stack 20 preferably reaches the temperature of a completed heating cycle, while that of the anode gas circulator pump 55 does not. Consequently, condensation occurs in the anode gas circulator pump 55 due to a temperature difference between the anode exhaust gas and the pump, resulting in the accumulation of a large amount of liquid water.If it is determined that the low-load operation has not been completed, the process returns to step S322 and the low-load operation continues. If it is determined that the low-load operation has been completed, the process proceeds to step S326.

[0038] In step S326, the controller 80 performs a no-power operation. "No-power operation" refers to an operation of the fuel cell system 10 in which the power generation of the fuel cell stack 20 is stopped, while the anode gas continues to circulate in the anode gas circulation flow path 62. For example, when the no-power operation is performed, the hydrogen supply from the injector 54 is stopped, but the anode gas circulation pump 55 continues to operate, so that the anode gas circulates. The no-power operation can also be performed as "discontinuous operation." Discontinuous operation refers to an operation in which the power generation of the fuel cell stack 20 is temporarily stopped, while the fuel cell system 10 continues to operate.During intermittent or non-power-generating operation, the fuel cell stack 20 can generate a small current to prevent the voltage of the unit cell 24 from becoming an open-circuit voltage. Such operation essentially involves no power generation and can therefore also be considered "intermittent operation" or "non-power-generating operation." During non-power-generating operation, the cathode gas supply can be continued or stopped.

[0039] If the temperature of the fuel cell stack 20 or the anode gas circulation flow path 62 has fallen to a sufficiently low temperature before the low-load operation begins in step S322, the temperature of the anode gas circulation flow path 62, including the anode gas circulation pump 55 and the gas-liquid separator 56, will not reach the temperature of a completed heating cycle if the temperature of the fuel cell stack 20 reaches the temperature of a completed heating cycle due to the low-load operation. Therefore, if highly humid anode gas, expelled from the fuel cell stack 20, flows through the anode gas circulation flow path 62, condensation will occur in the anode gas circulation flow path 62, causing liquid water to accumulate therein.In particular, the anode gas circulating pump 55 and the gas-liquid separator 56 are likely to be kept at a lower temperature than pipes, thereby promoting the accumulation of liquid water in such components.

[0040] In step S328, the controller 80 determines whether the non-power-generating operation has ended. For example, a termination condition for non-power-generating operation may be met when a time period for the accumulation of a sufficient quantity of liquid water in the anode gas recirculation flow path 62 has elapsed. For example, the time period for the accumulation of a sufficient quantity of liquid water is set to between three and seven minutes inclusive. If it is determined that the non-power-generating operation has not ended, the process returns to step S326 and the non-power-generating operation continues. If it is determined that the non-power-generating operation has ended, the process is in Fig. 4 completed and the process in Fig. 3 proceeds to step S330.

[0041] Instead of low-load operation and non-power-generating operation under the above condition, where liquid water accumulates, another operating mode can be implemented under different conditions where liquid water accumulates. For example, the liquid water accumulation process can be carried out by having the fuel cell system perform a preheating operation while the ambient temperature is lowered below freezing. In this mode, it is possible to accumulate a larger quantity of liquid water by lowering the temperature of the anode gas supplied to the fuel cell stack below freezing.Under any condition in which liquid water accumulates, the temperature of the anode gas circulation pump 55 at the time when operation under the liquid water accumulation condition ends is preferably lower than the temperature of the fuel cell stack 20 by a predetermined temperature difference (for example, 10 °C) or more. This ensures that a large quantity of liquid water accumulates in the anode gas circulation flow path 62, including the anode gas circulation pump 55.

[0042] Back in Fig. In step S330, the controller 80 terminates the operation of the fuel cell system 10 after the liquid water accumulation process in step S320. In step S410, the controller 80 causes the fuel cell system 10 to enter standby mode until a restart condition is met. At the time of step S410, the operation of the anode gas supply recirculation system 50, the cathode gas supply / drainage system 30, and the coolant recirculation system 70 has been stopped. The standby state in this stopped state causes the water generated in the unit cells 24, which accumulated during low-load operation in step S322 ( Fig. 4) generated, is moved from the cathode side to the anode side by the membrane electrode arrangement. Therefore, the spatial volume of hydrogen in unit cell 24 decreases, and the residual amount of hydrogen decreases. Therefore, a hydrogen deficiency in unit cell 24 during the power generation described later is unlikely, so a negative voltage is easily detected.

[0043] When the coolant circulation system 70 is operated during standby to forcibly cool the fuel cell stack 20, the generated water is more likely to remain close to the cathode-side separator. This results in a smaller amount of water migrating to the anode side. The water generated on the cathode side is discharged to the outside of the unit cell 24 along with the cathode exhaust when the fuel cell system 10 is restarted. Therefore, it is preferred that the system be in standby mode with the coolant circulation system 70 stopped, thus increasing the amount of water on the anode side. During standby, nitrogen in the air also migrates from the cathode side to the anode side through the membrane electrode assembly, and hydrogen on the anode side migrates through the membrane electrode assembly to the cathode side to react with the air on the cathode side.

[0044] In step S420, the controller 80 determines whether the standby phase of the fuel cell system 10 has ended. For example, a standby end condition (or a restart condition) can be set to include at least one of the following: a condition that is met when a predetermined standby period has elapsed after the fuel cell system 10 has been stopped, and / or a condition that is met when the temperature of the fuel cell stack 20 falls to a predetermined standby end temperature. The "standby period" is a time long enough for the generated water to move sufficiently from the cathode side to the anode side and is set, for example, to between one hour and three hours inclusive.The "ready-state termination temperature" is the temperature at which the water vapor in the generated water sufficiently converts into liquid water and is set, for example, to between 30 °C and 40 °C inclusive. With a restart condition set in this way, a shorter verification period is achieved, during which sufficient water moves from the cathode side to the anode side of unit cell 24. If, in step S420, it is determined that the ready state has not yet been completed (the restart condition is not met), the process returns to step S410 and the ready state continues. If it is determined that the ready state has been completed (the restart condition is met), the process proceeds to step S510.

[0045] In step S510, the controller 80 restarts the fuel cell system 10. In step S520, the controller 80 performs a process in which anode gas is supplied to the fuel cell stack 20 before power generation by the fuel cell stack 20 begins, in order to replace gas remaining on the anode side of the unit cells 24 with the anode gas. Specifically, the controller 80 actuates the injector 54 and the anode gas recirculation pump 55 to supply hydrogen to the fuel cell stack 20, replacing nitrogen and a small amount of hydrogen remaining on the anode side of the unit cell 24 during the standby process in step S410 with the new hydrogen. When the anode gas circulation pump 55 starts operating, the liquid water accumulated in the anode gas circulation flow path 62 due to the accumulation process of liquid water in step S320 is fed to the anode gas supply opening 25 ( Fig. 1) of the fuel cell stack 20. The liquid water supplied to the anode gas supply opening 25 flows into the anode gas inlet flow path 111 ( Fig. 2) of the unit cells 24. Therefore, a unit cell 24 whose unit inlet flow path 111p has an excessively small flow cross-sectional area due to a manufacturing defect will be clogged by the liquid water. Note that step S520 can be omitted.

[0046] In step S530, the controller 80 causes the fuel cell stack 20 to generate current. The current generation is preferably carried out such that the fuel cell stack 20 generates a small current to prevent the voltage of the unit cell 24 from becoming the open-circuit voltage. For example, the current generation is carried out such that the current is between 3% and inclusive of 15% of the rated current of the fuel cell stack 20. While the fuel cell stack 20 continues to generate current, the hydrogen in the unit cell 24 is consumed. Consequently, because the anode gas inlet flow path 111 is blocked, the unit cell 24 has a negative voltage due to a lack of hydrogen. During current generation, the controller 80 causes the cell monitoring device 95 ( Fig. 1) The cell voltage of each of the unit cells 24 is measured to identify the unit cell with the negative voltage. The controller 80 is notified of the measurement result. The cell voltage of unit cell 24 can be measured after the current generation in step S530 has been completed.

[0047] In step S610, the controller 80 determines whether a negative voltage check period has elapsed. For example, the negative voltage check period is set to between 3 seconds and 10 seconds inclusive. If it is determined that the negative voltage check period has not yet elapsed, the process returns to step S530 and power generation continues. If it is determined that the negative voltage check period has elapsed, the process proceeds to step S620. In step S620, the cell voltage notification unit 82 of the controller 80 issues a notification indicating to a verification person the unit cell that has a negative voltage. For example, the notification preferably includes the position of unit cell 24 in the fuel cell stack 20 (cell number) and the value of the negative voltage.If the unit cell is detected with a negative voltage, a process such as disassembling the fuel cell stack 20 and replacing the unit cell with a new cell is carried out.

[0048] Fig. Figure 5 is a diagram illustrating an example of how the current generated by the fuel cell stack 20, the flow rate of supplied hydrogen, and the flow rate of circulating hydrogen change over time during the verification process for the fuel cell stack 20. The fuel cell system 10 performs low-load operation ( Fig. 4, step S322) during a period from time t0 to time t1. The operation is carried out with the fuel cell stack 20 generating a current I1 that is lower than the nominal current. Therefore, the injector 54 supplies hydrogen at a flow rate S1 and the anode gas circulation pump 55 circulates the hydrogen at a flow rate R1. The temperature of the fuel cell stack 20 reaches the temperature of a completed heating cycle at time t1.

[0049] Fuel cell system 10 performs non-power-generating operation ( Fig. 4, step S326) during a period between time t1 and time t2. The operation is carried out such that no electricity is generated by the fuel cell stack 20 and no hydrogen is supplied by the injector 54, and the anode gas circulation pump 55 still circulates the hydrogen at flow rate R1. When the anode gas circulation pump 55 is operated in this way, the water vapor generated due to the low-load operation flows into the anode gas circulation flow path 62 ( Fig. 1), which causes condensation, leading to the accumulation of liquid water in the anode gas circulation flow path 62. The fuel cell system 10 ceases operation at time t2.

[0050] The fuel cell system 10 remains in standby mode for a period between time t2 and time t3 ( Fig. 3, step S410). In this state, no current is generated by the fuel cell system 10, and the injector 54 and the anode gas circulation pump 55 are not operated. The water produced during low-load operation moves to the anode side of the unit cell 24, causing the liquid water to accumulate on the anode side.

[0051] The fuel cell system 10 carries out the hydrogen exchange in a period between time t3 and time t4 ( Fig. 3, step S520). In this state, no current is generated by the fuel cell stack 20, the injector 54 supplies the hydrogen at a flow rate S2, and the anode gas circulation pump 55 circulates the hydrogen at a flow rate R2 (= S2). When the anode gas circulation pump 55 is operated in this manner, the liquid water accumulated in the anode gas circulation flow path 62 and on the anode side of the unit cells 24 is drawn into the anode gas supply opening 25 ( Fig. 1) supplied to the fuel cell stack 20.

[0052] The fuel cell stack 20 generates electricity during a period between time t4 and time t5 ( Fig. 3, step S530). In this state, the fuel cell stack 20 generates current I3. Therefore, the injector 54 supplies the hydrogen at a flow rate S3, and the anode gas circulation pump 55 circulates the hydrogen at a flow rate R3. At time t5, the negative voltage monitoring time expires, and therefore the fuel cell system 10 stops.

[0053] Fig. Figure 6 is a diagram illustrating how the anode gas inlet flow path 111 of unit cell 24 ( Fig. 1) is blocked by the negative voltage of the liquid water. Fig. Figure 6 shows, as an example, a region VI within a dashed circle. Fig. 2. A projection 112 is formed between adjacent unit inlet flow paths 111p of the anode gas inlet flow path 111. Each projection 112 is divided in two by a gap 111m, which is thinner than the unit inlet flow path 111p.

[0054] As in Fig. As shown in Figure 6, the anode gas inlet flow paths 111p draw in the liquid water Wa in unit cell 24, which likely has the blocked anode gas inlet flow path 111, due to the gap 111m, when liquid water passing through steps S310 to S520 in Fig. The hydrogen that has accumulated in the anode gas supply port 25 of the fuel cell stack 20 flows through the anode gas inlet collector port 110 of the separator 100 into the unit inlet flow path 111, causing the anode gas inlet flow path 111 to become blocked. When current is generated with the anode gas inlet flow path 111 blocked, the unit cell 24 enters a hydrogen-deficient state and exhibits a negative voltage. Therefore, the unit cell 24 whose anode gas inlet flow path 111 is likely to be blocked is detected by detecting the unit cell 24 that exhibits the negative voltage.

[0055] As described above, in one embodiment of the present disclosure it is possible to detect the unit cell 24 whose anode gas inlet flow path 111 is likely to be blocked by detecting a unit cell 24 exhibiting negative voltage during the verification process for the fuel cell stack 20.

Claims

[1] A verification procedure for a fuel cell stack (20) comprising a plurality of unit cells (24), the procedure comprising the following steps: (a) Operating a fuel cell system (10) comprising the fuel cell stack (20) and an anode gas circulation flow path (62) arranged between an anode gas discharge port (26) and an anode gas supply port (25) of the fuel cell stack (20) to circulate anode gas under a predetermined condition in which liquid water is accumulated, in order to accumulate liquid water in the anode gas circulation flow path (62); (b) Following step (a), cause the fuel cell system (10) to stop and wait until a predetermined restart condition is met; and (c) Restarting the fuel cell system (10) after step (b) to implement power generation by the fuel cell stack (20) and measuring a voltage of each unit cell (24) to detect a unit cell (24) that has a negative voltage, wherein the operation under the liquid water accumulation condition in step (a) comprises: a low-load operation in which the fuel cell system (10) is operated such that the fuel cell stack (20) generates a current that is lower than a nominal current of the fuel cell stack (20); and a non-power-generating operation, which is carried out after low-load operation, in which the power generation by the fuel cell stack (20) is stopped and the fuel cell system (10) is operated in such a way that circulation of the anode gas in the anode gas circulation flow path (62) continues. [2] Verification method for a fuel cell stack (20) according to claim 1, wherein the low-load operation is carried out in such a way that the temperature of the fuel cell stack (20) rises to a predetermined heating temperature due to the low-load operation, while the temperature of an anode gas circulation pump (55) arranged in the anode gas circulation flow path (62) does not reach the temperature of a completed heating. [3] Verification method for a fuel cell stack (20) according to claim 1 or 2, wherein the restart condition comprises at least one condition that is met when a predetermined standby period elapses after the fuel cell system (10) has been stopped, and / or one condition that is met when the temperature of the fuel cell stack (20) falls to a predetermined standby end temperature. [4] Verification method for a fuel cell stack (20) according to one of claims 1 to 3, wherein step (a) is carried out to accumulate liquid water in an anode gas circulation pump (55) arranged in the anode gas circulation flow path (62). [5] Verification method for a fuel cell stack (20) according to any one of claims 1 to 4, wherein step (c) comprises supplying anode gas to the fuel cell stack (20) before the power generation by the fuel cell stack (20) begins in order to replace gas remaining on an anode side of the unit cells (24) with the anode gas. [6] A verification procedure for a fuel cell stack (20) comprising a plurality of unit cells (24), the procedure comprising the following steps: (a) Operating a fuel cell system (10) comprising the fuel cell stack (20) and an anode gas circulation flow path (62) arranged between an anode gas discharge port (26) and an anode gas supply port (25) of the fuel cell stack (20) to circulate anode gas under a predetermined condition in which liquid water is accumulated, in order to accumulate liquid water in the anode gas circulation flow path (62); (b) Following step (a), cause the fuel cell system (10) to stop and wait until a predetermined restart condition is met; and (c) Restarting the fuel cell system (10) after step (b) to implement power generation by the fuel cell stack (20) and measuring a voltage of each unit cell (24) to detect a unit cell (24) that has a negative voltage, wherein step (c) includes supplying anode gas to the fuel cell stack (20) before power generation by the fuel cell stack (20) begins in order to replace any gas remaining on an anode side of the unit cells (24) with the anode gas.

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