Fuel cell system and control method for fuel cell system

Abstract

To appropriately carry out drainage from a fuel cell stack.SOLUTION: If a determination unit 146 determines that a fuel cell stack 12 is in a wet state, a control unit 142 carries out drainage in a first drainage mode during standby power generation. If the determination unit 146 determines that the fuel cell stack 12 is not in the wet state, the control unit 142 executes drainage in a second drainage mode during standby power generation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system and a method for controlling a fuel cell system. [Background technology]

[0002] In recent years, research and development into fuel cells has been conducted to contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] A power generation system equipped with a fuel cell stack is called a fuel cell system. A fuel cell stack includes multiple power generation cells. The power generation cells generate electricity through an electrochemical reaction between fuel gas (hydrogen-containing gas) and oxidant gas (oxygen-containing gas). When the power generation cells generate electricity, water is produced. The produced water accumulates in the fuel cell stack, etc. If the operation of the fuel cell system is stopped in a low-temperature environment, there is a risk that the water accumulated in the fuel cell stack, etc. will freeze. If water freezes in the fuel cell system, etc., the flow of gas is obstructed, and the fuel cell stack will no longer be able to generate electricity.

[0004] Patent Document 1 discloses that scavenging is performed when the operation of a fuel cell system is finished. Scavenging is a process of discharging impurities such as water and nitrogen from the fuel cell stack. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-180076 Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable to properly drain water from the fuel cell stack.

[0007] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0008] A first invention is a fuel cell system comprising: a fuel cell stack having a plurality of power generation cells that generate power using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; a discharge path through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor that detects a stack temperature that is the temperature of the fuel cell stack; and a control device that controls the oxidant gas supplier. The control device comprises a control unit that performs power generation during shutdown that continues power generation by the power generation cells after receiving an instruction to stop power generation until a predetermined condition is satisfied; an acquisition unit that acquires the stack temperature before power generation during shutdown; and a control unit that determines whether the fuel cell stack is in a wet state based at least on the stack temperature acquired by the acquisition unit. and a determination unit that determines whether or not the control unit should perform drainage in a first drainage mode during the power generation during shutdown, wherein the control unit is capable of selectively performing either drainage in a first drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate, or drainage in a second drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, and if the determination unit determines that the fuel cell stack is in the wet state, the control unit performs drainage in the first drainage mode during the power generation during shutdown, and if the determination unit determines that the fuel cell stack is not in the wet state, the control unit performs drainage in the second drainage mode during the power generation during shutdown.

[0009] A second invention is a control method for a fuel cell system including a fuel cell stack having a plurality of power generation cells that generate power using an oxidant gas and a fuel gas, an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack, a supply path through which the oxidant gas supplied to the fuel cell stack flows, a discharge path through which the oxidant gas discharged from the fuel cell stack flows, a temperature sensor that detects a stack temperature that is the temperature of the fuel cell stack, and a control device that controls the oxidant gas supplier, wherein the control device performs stoppage power generation in which power generation by the power generation cells continues from when a command to stop power generation is received until a predetermined condition is satisfied, acquires the stack temperature before the stoppage power generation, and performs the above-mentioned control based at least on the acquired stack temperature before the stoppage power generation. The system is capable of determining whether the fuel cell stack is in a wet state, and selectively performing either a first drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate during the stopped power generation, or a second drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate.If it is determined that the fuel cell stack is in the wet state, drainage is performed in the first drainage mode during the stopped power generation, and if it is determined that the fuel cell stack is not in the wet state, drainage is performed in the second drainage mode during the stopped power generation. [Effects of the Invention]

[0010] According to the present invention, water can be appropriately drained from the fuel cell stack. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] FIG. 2 is an exploded perspective view of a power generating cell provided in the fuel cell stack. [Figure 3] FIG. 3 is a schematic diagram of the first separator. [Figure 4] FIG. 4 is a schematic diagram of the second separator. [Figure 5] FIG. 5 is a flowchart of the fuel cell stack wetness determination process. [Figure 6] FIG. 6 is a diagram showing a wetness determination map. [Figure 7] Fig. 7A is a diagram showing the change over time of the current indication value, Fig. 7B is a diagram showing the change over time of the cooling medium temperature value, Fig. 7C is a diagram showing the change over time of the time measured by the timer, and Fig. 7D is a diagram showing the change over time of the wet flag. [Figure 8] FIG. 8 is a flowchart of the drainage process executed during power generation during shutdown. DETAILED DESCRIPTION OF THE INVENTION

[0012] [1 Configuration of fuel cell system 10] FIG. 1 is a schematic diagram of a fuel cell system 10. The fuel cell system 10 is mounted on, for example, a vehicle (fuel cell vehicle). Alternatively, the fuel cell system 10 can also be mounted on ships, aircraft, robots, etc. The fuel cell system 10 can also be used as a power source for facilities, homes, etc.

[0013] In the fuel cell system 10, a fuel gas and an oxidant gas are used as reactant gases. The fuel gas is a hydrogen-containing gas. The oxidant gas is an oxygen-containing gas such as air. Each of the fuel gas and the oxidant gas is supplied to the fuel cell stack 12 and subjected to an electrochemical reaction. In this specification, the fuel gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as fuel off-gas. In this specification, the oxidant gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as oxidant off-gas.

[0014] The fuel cell system 10 includes a fuel cell stack 12, a tank 14, an anode system 16, a cathode system 18, and a cooling system 20. The fuel cell system 10 also includes a control device 22. Electric power generated by the fuel cell stack 12 is supplied to a load 21. The tank 14 is filled with high-pressure fuel gas.

[0015] The fuel cell stack 12 includes a fuel gas supply port 22a that supplies fuel gas to the interior of the fuel cell stack 12, and a fuel gas discharge port 22b that discharges fuel off-gas from the interior of the fuel cell stack 12. The fuel cell stack 12 includes an oxidant gas supply port 22c that supplies oxidant gas to the interior of the fuel cell stack 12, and an oxidant gas discharge port 22d that discharges oxidant off-gas from the interior of the fuel cell stack 12. The fuel cell stack 12 includes a coolant supply port 22e that supplies a coolant to the interior of the fuel cell stack 12, and a coolant discharge port 22f that discharges the coolant from the interior of the fuel cell stack 12. The fuel cell stack 12 includes a drain port 22g that drains water remaining inside the fuel cell stack 12. The drain port 22g is located at the bottom of the fuel cell stack 12.

[0016] The configuration of the fuel cell stack 12 will now be described with reference to Figs. 2 to 4. Fig. 2 is an exploded perspective view of a power generating cell 24 provided in the fuel cell stack 12. The fuel cell stack 12 is formed by stacking a plurality of power generating cells 24 in the direction of arrow A. A compressive load is applied to the fuel cell stack 12 in the stacking direction of the plurality of power generating cells 24.

[0017] The power generating cell 24 has a horizontally long rectangular shape. The power generating cell 24 includes a membrane electrode assembly 26 and a pair of separators (a first separator 28 and a second separator 30). The surface 28a of the first separator 28 faces the first surface 26a of the membrane electrode assembly 26. The surface 30a of the second separator 30 faces the second surface 26b of the membrane electrode assembly 26. The membrane electrode assembly 26 is sandwiched between the first separator 28 and the second separator 30.

[0018] The first separator 28 and the second separator 30 are formed from a metal sheet having a corrugated cross section. In two adjacent power generating cells 24, the first separator 28 of one power generating cell 24 and the second separator 30 of the other power generating cell 24 are joined together. A refrigerant flow path (not shown) through which a cooling medium flows is formed between the first separator 28 and the second separator 30.

[0019] The membrane electrode structure 26 includes a membrane electrode assembly (MEA) 32 and a resin frame 34. The MEA 32 includes an electrolyte membrane 36, a cathode electrode 40, and an anode electrode 38. The electrolyte membrane 36 is interposed between the cathode electrode 40 and the anode electrode 38. The resin frame 34 protrudes outward from the outer periphery of the MEA 32.

[0020] An oxidant gas supply passage 42a, a coolant supply passage 44a, and a fuel gas discharge passage 46b are arranged at one edge of the long side of the power generation cell 24 (the edge in the direction of arrow B1). The oxidant gas supply passage 42a communicates with the oxidant gas supply port 22c. Oxidant gas flows through the oxidant gas supply passage 42a in the direction of arrow A2. The coolant supply passage 44a communicates with the coolant supply port 22e. A coolant flows through the coolant supply passage 44a in the direction of arrow A2. The fuel gas discharge passage 46b communicates with the fuel gas discharge port 22b. Fuel gas flows through the fuel gas discharge passage 46b in the direction of arrow A1.

[0021] A fuel gas supply passage 46a, a coolant discharge passage 44b, and an oxidant gas discharge passage 42b are arranged at the other edge of the long side of the power generation cell 24 (the edge in the direction of arrow B2). The fuel gas supply passage 46a communicates with the fuel gas supply port 22a. Fuel gas flows through the fuel gas supply passage 46a in the direction of arrow A2. The coolant discharge passage 44b communicates with the coolant discharge port 22f. The coolant flows through the coolant discharge passage 44b in the direction of arrow A1. The oxidant gas discharge passage 42b communicates with the oxidant gas discharge port 22d. Oxidant gas flows through the oxidant gas discharge passage 42b in the direction of arrow A1.

[0022] FIG. 3 is a schematic diagram of the first separator 28. FIG. 3 shows the surface 28a of the first separator 28. The first separator 28 is formed in a rectangular shape. An oxidant gas flow field 50 is formed on the surface 28a of the first separator 28. When viewed from the direction of arrow A1 or arrow A2 shown in FIG. 2, the oxidant gas flow field 50 overlaps with the cathode 40 of the membrane electrode assembly 26. The oxidant gas flow field 50 extends in the direction of the long side of the power generation cell 24 (the direction of arrow B).

[0023] The oxidant gas flow field 50 includes a plurality of first flow field protrusions 52 and a plurality of first flow field grooves 54. The first flow field protrusions 52 protrude in the direction of arrow A2. The first flow field grooves 54 are recessed in the direction of arrow A1. The first flow field protrusions 52 and the first flow field grooves 54 each extend in a wavy pattern in the direction of arrow B. In the oxidant gas flow field 50, the first flow field protrusions 52 and the first flow field grooves 54 are alternately arranged in the flow field width direction (the direction of arrow C).

[0024] Two first feed portions 55a, 55b are formed on the surface 28a of the first separator 28. The first feed portion 55a has a plurality of first feed protrusions 56a and a plurality of first feed grooves 57a extending from the oxygen-containing gas supply passage 42a toward the oxygen-containing gas flow field 50. The first feed portion 55b has a plurality of first feed protrusions 56b and a plurality of first feed grooves 57b extending from the oxygen-containing gas flow field 50 toward the oxygen-containing gas discharge passage 42b.

[0025] A first seal portion 58 for preventing leakage of the reactant gas (oxidant gas or fuel gas) or the coolant is formed on the surface 28a of the first separator 28. The first seal portion 58 includes a plurality of first communication hole seal portions 60 and a first flow path seal portion 62. The first communication hole seal portions 60 and the first flow path seal portions 62 protrude in the direction of arrow A2. One first communication hole seal portion 60 is formed for each communication hole (such as the oxidant gas supply passage 42a). Each first communication hole seal portion 60 surrounds an individual communication hole. The first flow path seal portion 62 surrounds the area where the oxidant gas flow field 50, the first feed portions 55a, 55b, and the communication holes through which the reactant gas flows (the oxidant gas supply passage 42a, the oxidant gas discharge passage 42b, the fuel gas supply passage 46a, and the fuel gas discharge passage 46b) are located. Each of the plurality of first communication hole seals 60 and the first flow path seals 62 is pressed against the resin frame 34 of the membrane electrode assembly 26 .

[0026] The first hole seal part 60 surrounding the oxidant gas supply passage 42a includes a tunnel 63a. The tunnel 63a connects the oxidant gas supply passage 42a to the first feed section 55a adjacent to the oxidant gas supply passage 42a. Although one tunnel 63a is shown in FIG. 3, multiple tunnels 63a are actually provided. Similarly, the first hole seal part 60 surrounding the oxidant gas discharge passage 42b includes a tunnel 63b. The tunnel 63b connects the oxidant gas discharge passage 42b to the first feed section 55b adjacent to the oxidant gas discharge passage 42b. Although one tunnel 63b is shown in FIG. 3, multiple tunnels 63b are actually provided.

[0027] The oxidant gas is supplied from the oxidant gas supply passage 42a through the tunnel 63a and the first feed portion 55a to the oxidant gas flow field 50. The oxidant gas flows through the oxidant gas flow field 50 and is supplied to the cathode 40. Oxidant off-gas that is not used in the electrochemical reaction is discharged from the oxidant gas flow field 50 through the first feed portion 55b and the tunnel 63b to the oxidant gas discharge passage 42b.

[0028] A first bypass stopper convex portion 64 is formed on the surface 28a of the first separator 28. The first bypass stopper convex portion 64 is disposed between the end portion (first end flow path protrusion 52a) of the oxidant gas flow path 50 in the flow path width direction and the first flow path seal portion 62. The first bypass stopper convex portion 64 prevents the oxidant gas supplied from the oxidant gas supply passage 42a from flowing between the first end flow path protrusion 52a and the first flow path seal portion 62 and being supplied to the oxidant gas discharge passage 42b. In other words, the first bypass stopper convex portion 64 prevents the oxidant gas from bypassing.

[0029] The first bypass stopper convex portion 64 has a plurality of first bypass protrusions 65 extending in the direction of arrow C. The plurality of first bypass protrusions 65 are arranged along the direction of arrow B. The first bypass protrusions 65 protrude in the direction of arrow A2. The height of the first bypass protrusions 65 is slightly lower than the height of the first flow path seal portion 62. The first bypass protrusions 65 are not subjected to a compressive load in the direction of arrow A. Therefore, a small gap is present between the first bypass protrusions 65 and the resin frame portion 34 of the membrane electrode assembly 26.

[0030] FIG. 4 is a schematic diagram of the second separator 30. FIG. 4 shows the surface 30a of the second separator 30. The second separator 30 is formed in a rectangular shape. A fuel gas flow field 66 is formed on the surface 30a of the second separator 30. When viewed from the direction of arrow A1 or arrow A2 shown in FIG. 2, the fuel gas flow field 66 overlaps with the anode 38 of the membrane electrode assembly 26. The fuel gas flow field 66 extends in the direction of the long side of the power generation cell 24 (the direction of arrow B).

[0031] The fuel gas flow field 66 includes a plurality of second flow field protrusions 68 and a plurality of second flow field grooves 70. The second flow field protrusions 68 protrude in the direction of arrow A1. The second flow field grooves 70 are recessed in the direction of arrow A2. Each of the second flow field protrusions 68 and the second flow field grooves 70 extends in a wavy pattern in the direction of arrow B. In the fuel gas flow field 66, the second flow field protrusions 68 and the second flow field grooves 70 are alternately arranged in the flow field width direction (the direction of arrow C).

[0032] Two second feed sections 71a, 71b are formed on the surface 30a of the second separator 30. The second feed section 71a has multiple second feed protrusions 72a and multiple second feed grooves 73a extending from the fuel gas supply passage 46a toward the fuel gas flow field 66. The second feed section 71b has multiple second feed protrusions 72b and multiple second feed grooves 73b extending from the fuel gas flow field 66 toward the fuel gas discharge passage 46b.

[0033] The second separator 30 has a second seal portion 74 formed on its surface 30a to prevent leakage of the reactant gas (oxidant gas or fuel gas) or the coolant. The second seal portion 74 includes a plurality of second communication hole seal portions 76 and a second flow path seal portion 78. The second communication hole seal portions 76 and the second flow path seal portions 78 protrude in the direction of arrow A1. One second communication hole seal portion 76 is formed for each communication hole (such as the fuel gas supply passage 46a). Each second communication hole seal portion 76 surrounds an individual communication hole. The second flow path seal portion 78 surrounds the area where the fuel gas flow path 66, the second feed portions 71a, 71b, and the communication holes through which the reactant gas flows (the oxidant gas supply passage 42a, the oxidant gas discharge passage 42b, the fuel gas supply passage 46a, and the fuel gas discharge passage 46b) are located. Each of the plurality of second communication hole seals 76 and the second flow path seals 78 is pressed against the resin frame 34 of the membrane electrode assembly 26 .

[0034] The second communication hole seal portion 76 surrounding the fuel gas supply passage 46a includes a tunnel 79a. The tunnel 79a connects the fuel gas supply passage 46a to the second feed section 71a adjacent to the fuel gas supply passage 46a. Although one tunnel 79a is shown in FIG. 4, multiple tunnels 79a are actually provided. Similarly, the second communication hole seal portion 76 surrounding the fuel gas discharge passage 46b includes a tunnel 79b. The tunnel 79b connects the fuel gas discharge passage 46b to the second feed section 71b adjacent to the fuel gas discharge passage 46b. Although one tunnel 79b is shown in FIG. 4, multiple tunnels 79b are actually provided.

[0035] The fuel gas is supplied from the fuel gas supply passage 46a through the tunnel 79a and the second feed section 71a to the fuel gas flow passage 66. The fuel gas flows through the fuel gas flow passage 66 and is supplied to the anode 38. The fuel off-gas that is not used in the electrochemical reaction is discharged from the fuel gas flow passage 66 through the second feed section 71b and the tunnel 79b to the fuel gas discharge passage 46b.

[0036] The surface 30a of the second separator 30 has a second bypass stopper convex portion 80 formed thereon. The second bypass stopper convex portion 80 is disposed between the end of the fuel gas flow field 66 in the flow field width direction (the second end flow field protrusion 68a) and the second flow field seal portion 78. The second bypass stopper convex portion 80 prevents fuel gas supplied from the fuel gas supply passage 46a from flowing between the second end flow field protrusion 68a and the second flow field seal portion 78 and being supplied to the fuel gas discharge passage 46b. In other words, the second bypass stopper convex portion 80 prevents fuel gas from bypassing.

[0037] The second bypass stopper convex portion 80 has a plurality of second bypass projections 82 extending in the direction of arrow C. The plurality of second bypass projections 82 are arranged along the direction of arrow B. The second bypass projections 82 project in the direction of arrow A1. The height of the second bypass projections 82 is slightly lower than the height of the second flow path seal portion 78. The second bypass projections 82 are not subjected to a compressive load in the direction of arrow A. Therefore, a minute gap is present between the second bypass projections 82 and the resin frame portion 34 of the membrane electrode assembly 26.

[0038] Returning to Figure 1, the configuration of the fuel cell system 10 will be described. The anode system 16 includes a fuel gas supply channel 84, a fuel gas discharge channel 86, a circulation channel 88, a first drain channel 90, and a second drain channel 92. The anode system 16 also includes an injector 94, an ejector 96, a gas-liquid separator 98, a first drain valve 100, and a second drain valve 102.

[0039] The fuel gas supply path 84 is connected to the outlet of the tank 14 and the fuel gas supply port 22a of the fuel cell stack 12. The fuel gas supply path 84 is provided with an injector 94 and an ejector 96. The ejector 96 is disposed closer to the fuel cell stack 12 than the injector 94.

[0040] The fuel gas discharge path 86 is connected to the fuel gas discharge port 22b of the fuel cell stack 12 and a supply port of a gas-liquid separator 98. The circulation path 88 is connected to the discharge port of the gas-liquid separator 98 and the ejector 96.

[0041] The first drainage channel 90 is connected to the drain outlet of the gas-liquid separator 98 and to the inlet of the diluter 121. The outlet of the diluter 121 is connected to an exhaust port provided in the vehicle. The first drainage channel 90 is provided with a first drainage valve 100. The second drainage channel 92 is connected to the drainage port 22g of the fuel cell stack 12 and the first drainage channel 90. The second drainage channel 92 is provided with a second drainage valve 102.

[0042] The cathode system 18 includes an oxidant gas supply channel 106, an oxidant gas discharge channel 108 (discharge channel), and a bypass channel 110. The cathode system 18 also includes a compressor 112 (oxidant gas supplier), a humidifier (HUM) 114, a first shutoff valve 116, a second shutoff valve 118, and a bypass valve 120.

[0043] The oxidant gas supply channel 106 is connected to an air intake port provided in the vehicle and the oxidant gas supply port 22c of the fuel cell stack 12. The oxidant gas supply channel 106 is provided with a compressor 112, a first shut-off valve 116, and a humidifier supply channel 114A for the humidifier 114. A portion of the oxidant gas supply channel 106 that is arranged upstream of the humidifier 114 is referred to as the oxidant gas supply channel 106A. A portion of the oxidant gas supply channel 106 that is arranged downstream of the humidifier 114 is referred to as the oxidant gas supply channel 106B. The oxidant gas supply channel 106A is provided with the compressor 112 and the first shut-off valve 116. The first shut-off valve 116 is arranged closer to the humidifier 114 than the compressor 112.

[0044] The oxidant gas discharge channel 108 is connected to the oxidant gas discharge port 22d of the fuel cell stack 12 and to the inlet of the diluter 121. The oxidant gas discharge channel 108 is provided with a humidifier discharge channel 114B of the humidifier 114 and a second shutoff valve 118. A portion of the oxidant gas discharge channel 108 that is arranged upstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108A. A portion of the oxidant gas discharge channel 108 that is arranged downstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108B. The oxidant gas discharge channel 108B is provided with the second shutoff valve 118.

[0045] The bypass passage 110 is connected to the oxidizing gas supply passage 106A between the compressor 112 and the first shutoff valve 116, and to the oxidizing gas discharge passage 108B downstream of the second shutoff valve 118. The bypass passage 110 is provided with a bypass valve 120.

[0046] The anode system 16 and the cathode system 18 are connected to each other by a connection line 132. The connection line 132 is connected to the circulation line 88 of the anode system 16 and the oxidant gas supply line 106B of the cathode system 18. A bleed valve 134 is provided in the connection line 132.

[0047] The cooling system 20 includes a coolant supply path 122 and a coolant discharge path 124. The cooling system 20 also includes a pump 126, a radiator 128, and a temperature sensor 130.

[0048] The cooling medium supply path 122 is connected to a fluid outlet of the radiator 128 and a cooling medium supply port 22e of the fuel cell stack 12. A pump 126 is provided in the cooling medium supply path 122. The cooling medium discharge path 124 is connected to a cooling medium discharge port 22f of the fuel cell stack 12 and a fluid supply port of the radiator 128. A temperature sensor 130 is attached to the cooling medium discharge path 124. The temperature sensor 130 detects the temperature of the cooling medium flowing through the cooling medium discharge path 124. The temperature of the cooling medium flowing through the cooling medium discharge path 124 corresponds to the temperature inside the fuel cell stack 12 (stack temperature).

[0049] An impedance measuring device 148 may be attached to the fuel cell stack 12. For example, the impedance measuring device 148 measures the impedance of the fuel cell stack 12 by superimposing an AC current on the outputs of the multiple power generating cells 24.

[0050] The control device 22 may be configured by an ECU (Electronic Control Unit). The control device 22 includes a calculation unit 136 and a storage unit 138. The calculation unit 136 is, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). That is, the calculation unit 136 may be configured by processing circuitry. The calculation unit 136 controls each device by executing a program stored in the storage unit 138. At least a part of the calculation unit 136 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). At least a part of the calculation unit 136 may be realized by an electronic circuit including discrete devices.

[0051] The calculation unit 136 includes an acquisition unit 140, a control unit 142, a timing unit 144, and a determination unit 146. The acquisition unit 140 acquires information from electronic components (sensors, ECU, etc.) other than the control device 22. The control unit 142 controls the operation of the injector 94, compressor 112, pump 126, various valves, etc. The timing unit 144 measures the execution time of the drainage control, which will be described later, using a timer. The determination unit 146 determines whether the fuel cell stack 12 is in an expected wet state or not, and whether it is in a wet state or not.

[0052] The storage unit 138 is configured by a volatile memory (not shown) and a nonvolatile memory (not shown), which are computer-readable storage media. The volatile memory is, for example, a random access memory (RAM). The nonvolatile memory is, for example, a read-only memory (ROM), a flash memory, etc. Data and the like are stored in, for example, the volatile memory. Programs, tables, maps, etc. are stored in, for example, the nonvolatile memory. At least a part of the storage unit 138 may be provided in the above-mentioned processor, integrated circuit, etc.

[0053] [2. Fluid flow in fuel cell system 10] 2-1 Fluid flow in the anode system 16 The injector 94 injects the fuel gas supplied from the tank 14 downstream of the fuel gas supply path 84. The fuel gas injected from the injector 94 is supplied to the fuel gas supply port 22a of the fuel cell stack 12 via the fuel gas supply path 84. The fuel gas that does not react inside the fuel cell stack 12 is discharged as fuel off-gas from the fuel gas discharge port 22b of the fuel cell stack 12. The fuel off-gas contains hydrogen that did not react with oxygen, nitrogen in the oxidant gas that has permeated the electrolyte membrane 36, and moisture produced by the reaction between oxygen and hydrogen.

[0054] The fuel off-gas is supplied to a gas-liquid separator 98 via a fuel gas discharge path 86. The gas-liquid separator 98 separates the fuel off-gas into a gas component (fuel off-gas) and a liquid component (water). The fuel off-gas discharged from the gas-liquid separator 98 is supplied to an ejector 96 via a circulation path 88. In the ejector 96, the fuel off-gas sucked from the gas-liquid separator 98 and the fuel gas injected from the injector 94 join together.

[0055] [2-2 Fluid flow in the cathode system 18] The compressor 112 discharges oxidant gas (air) taken in from outside the vehicle downstream of the oxidant gas supply channel 106. The oxidant gas discharged from the compressor 112 is supplied to the oxidant gas supply port 22c of the fuel cell stack 12 via the oxidant gas supply channel 106. The oxidant gas that has not reacted inside the fuel cell stack 12 is discharged as oxidant off-gas from the oxidant gas discharge port 22d of the fuel cell stack 12. The oxidant off-gas contains each component contained in the oxidant gas and moisture produced by the reaction of oxygen and hydrogen.

[0056] The oxidant off-gas is discharged to the diluter 121 via the oxidant gas discharge path 108. The oxidant off-gas contains moisture. In the humidifier 114, a portion of the moisture contained in the oxidant off-gas is used to humidify the oxidant gas flowing through the humidifier supply path 114A.

[0057] 2-3 Fluid flow in the cooling system 20 The pump 126 discharges the cooling medium toward the cooling medium supply port 22e of the fuel cell stack 12. The cooling medium discharged from the pump 126 is supplied to the cooling medium supply port 22e of the fuel cell stack 12 via the cooling medium supply path 122. The cooling medium that has circulated inside the fuel cell stack 12 is discharged from the cooling medium discharge port 22f of the fuel cell stack 12. The cooling medium discharged from the cooling medium discharge port 22f is supplied to the radiator 128 via the cooling medium discharge path 124. The cooling medium that has dissipated heat in the radiator 128 is drawn into the pump 126.

[0058] [3 Drainage during power generation shutdown] When the vehicle is stopped, the control device 22 stops the operation of the fuel cell system 10. Before stopping power generation by the fuel cell system 10, the calculation unit 136 (control unit 142) of the control device 22 performs power generation to bring the electrolyte membrane 36 to an appropriate wet state and to wet the electrolyte membrane 36 evenly. This is called power generation during stoppage. During power generation during stoppage, the control unit 142 controls power generation so that the output current value of the fuel cell stack 12 becomes a predetermined value. During power generation during stoppage, fuel gas, oxidant gas, and coolant are supplied to the fuel cell stack 12, and power is supplied from the fuel cell stack 12 to a load 21 (e.g., a battery).

[0059] Furthermore, the control unit 142 drains water from the fuel cell stack 12 during power generation during shutdown. This is also referred to as scavenging. For example, the control unit 142 drains water from the fuel cell stack 12 and each discharge path by increasing the flow rate of the reactant gas compared to normal power generation. Specifically, the control unit 142 controls the flow rate of the oxidant gas discharged from the compressor 112 (the flow rate of the oxidant gas supplied to the fuel cell stack 12). Note that water can be drained from the fuel cell stack 12 even if the flow rate of the fuel gas is increased. However, increasing the flow rate of the fuel gas during power generation during shutdown results in unnecessary consumption of the fuel gas. Therefore, it is preferable to drain water from the fuel cell stack 12 by increasing the amount of oxidant gas. In this specification, control to drain water from the fuel cell stack 12 (and the oxidant gas discharge path 108) during power generation during shutdown is referred to as drainage control or scavenging control. Note that water includes liquid water remaining in the fuel cell stack 12 and the oxidant gas discharge path 108, as well as humid air containing water vapor.

[0060] During power generation during shutdown, the control unit 142 can execute drainage control in the cathode system 18 in either a first drainage mode or a second drainage mode. If the determination unit 146 determines that the fuel cell stack 12 is in a wet state, the control unit 142 executes drainage in the first drainage mode. If the determination unit 146 determines that the fuel cell stack 12 is not in a wet state, the control unit 142 executes drainage in the second drainage mode. A wet state refers to a state in which the water content in the fuel cell stack 12 is equal to or greater than a predetermined amount, and a state in which the humidity inside the fuel cell stack 12 is equal to or greater than a predetermined humidity.

[0061] In the first drainage mode, the oxidant gas is discharged from the compressor 112 at a first flow rate. In the second drainage mode, the oxidant gas is discharged from the compressor 112 at a second flow rate. The first flow rate is greater than the second flow rate. Therefore, more water can be discharged from the fuel cell stack 12 in the first drainage mode than in the second drainage mode.

[0062] For example, water is likely to accumulate in the first bypass stopper convex portion 64 and the first feed portions 55a, 55b shown in FIG. 3 . Increasing the flow rate of oxidant gas to the fuel cell stack 12 reduces the water content of the electrolyte membrane 36. As a result, the water accumulated in the first bypass stopper convex portion 64 is absorbed by the electrolyte membrane 36 and is more likely to be discharged to the oxidant gas flow field 50. The water discharged to the oxidant gas flow field 50 is drained to the outside of the fuel cell stack 12. In other words, drainage in the first drainage mode can facilitate the drainage of water accumulated in the first bypass stopper convex portion 64. Furthermore, drainage in the first drainage mode can facilitate the drainage of water accumulated in the first feed portions 55a, 55b.

[0063] Similarly, water is likely to accumulate in the second bypass stopper convex portion 80 and the second feed portions 71a, 71b, etc., shown in FIG. 4. When the flow rate of the oxidant gas to the fuel cell stack 12 is increased, the water that accumulates in the second bypass stopper convex portion 80, etc., is absorbed by the electrolyte membrane 36 and is more likely to be discharged to the oxidant gas flow field 50. The water discharged to the oxidant gas flow field 50 is drained to the outside of the fuel cell stack 12. In other words, by performing drainage in the first drainage mode, it is possible to promote the drainage of water that accumulates in the second bypass stopper convex portion 80. Furthermore, by performing drainage in the first drainage mode, it is possible to promote the drainage of water that accumulates in the second feed portions 71a, 71b.

[0064] [3-1 Wetness determination of fuel cell stack 12] Fig. 5 is a flowchart of the wetness determination process for the fuel cell stack 12. Fig. 6 is a diagram showing the wetness determination map 150. Fig. 7A is a diagram showing the change over time of the current command value. Fig. 7B is a diagram showing the change over time of the cooling medium temperature value. Fig. 7C is a diagram showing the change over time of the time measured by the timer. Fig. 7D is a diagram showing the change over time of the wetness flag.

[0065] As described above, whether to perform drainage in the first drainage mode or the second drainage mode is determined based on whether the fuel cell stack 12 is in a wet state. Whether the fuel cell stack 12 is in a wet state is determined while the fuel cell system 10 is operating (while the vehicle is operating). An example of determining whether the fuel cell stack 12 is wet will be described with reference to FIG. 5.

[0066] In the wetness determination process described with reference to FIG. 5, the fuel cell stack 12 is determined to be in a wet state if the expected wet state continues for a predetermined time. The expected wet state refers to a state in which the fuel cell stack 12 is likely to become wet. Here, the expected wet state is determined based on the output current of the fuel cell stack 12 and the temperature of the fuel cell stack 12. The output current of the fuel cell stack 12 is substantially equal to the current command value from the vehicle's ECU. The temperature of the fuel cell stack 12 is substantially equal to the temperature of the fluid discharged from the fuel cell stack 12. Therefore, in the wetness determination process described below, whether or not the fuel cell stack 12 is in an expected wet state is determined based on the current command value (output current value) from the vehicle's ECU and the temperature value (stack temperature) detected by the temperature sensor 130. The temperature of the oxidant off-gas may be used instead of the temperature of the coolant.

[0067] In step S1, the determination unit 146 determines whether the fuel cell stack 12 is in an expected wet state. The determination unit 146 uses, for example, a wetness determination map 150 shown in FIG. 6. The wetness determination map 150 associates a combination of a current command value and a cooling medium temperature value with the state of the fuel cell stack 12 (whether the fuel cell stack is in an expected wet state or not). As shown in FIG. 6, the wetness determination map 150 associates a combination of a current command value less than the current threshold Ith and a cooling medium temperature value less than the temperature threshold Tth with the expected wet state. The wetness determination map 150 performs this association because the fuel cell stack 12 is likely to be in a wet state when the output current value of the fuel cell stack 12 is relatively small and the temperature of the fuel cell stack 12 is relatively low.

[0068] The acquisition unit 140 acquires a current command value for the fuel cell stack 12 from the vehicle's ECU. The acquisition unit 140 also acquires a temperature value of the cooling medium from the temperature sensor 130. The determination unit 146 determines whether the fuel cell stack 12 is in an expected wet state based on the current command value, the temperature value of the cooling medium, and a wetness determination map 150.

[0069] If the fuel cell stack 12 is in an expected wet state (step S1: YES), the process proceeds to step S2. For example, as shown in FIG. 7A, the current command value is less than the current threshold Ith between time t1 and time t2. Also, as shown in FIG. 7A, the current command value is less than the current threshold Ith between time t3 and time t4. Also, as shown in FIG. 7B, after time t1, the temperature value of the cooling medium is less than the temperature threshold Tth. The determination unit 146 determines that the fuel cell stack 12 is in an expected wet state between time t1 and time t2. Also, the determination unit 146 determines that the fuel cell stack 12 is in an expected wet state between time t3 and time t4.

[0070] On the other hand, if the fuel cell stack 12 is not in an expected wet state (step S1: NO), the process proceeds to step S7. For example, as shown in FIG. 7B, the temperature value of the cooling medium is greater than the temperature threshold value Tth between time t0 and time t1. Also, as shown in FIG. 7A, the current command value is greater than the current threshold value Ith between time t2 and time t3. The determination unit 146 determines that the fuel cell stack 12 is not in an expected wet state between time t0 and time t1. Also, the determination unit 146 determines that the fuel cell stack 12 is not in an expected wet state between time t2 and time t3.

[0071] In step S2, the timing unit 144 determines whether timing is in progress. If timing is in progress (step S2: YES), the process proceeds to step S4. On the other hand, if timing is not in progress (step S2: NO), the process proceeds to step S3.

[0072] When the process proceeds from step S2 to step S3, the timing unit 144 starts timing by the timer. For example, as shown in FIG. 7C, timing by the timer starts at time t1 and time t3. Note that timing by the timer continues between time t1 and time t2. Furthermore, timing by the timer continues between time t3 and time t4. When step S3 ends, the process proceeds to step S4.

[0073] When the process proceeds from step S2 or step S3 to step S4, the determination unit 146 compares the time measured by the timer with a predetermined time Cth. The predetermined time Cth is a time threshold for determining whether the fuel cell stack 12 is in a wet state. In the wetness determination process, if the expected wet state occurs continuously for the predetermined time Cth, the fuel cell stack 12 is determined to be in a wet state. If the measured time is equal to or greater than the predetermined time Cth (step S4: YES), the process proceeds to step S5. For example, as shown in FIG. 7C, at time t4, the time measured by the timer is equal to or greater than the predetermined time Cth. On the other hand, if the measured time is less than the predetermined time Cth (step S4: NO), the process returns to step S1.

[0074] When the process proceeds from step S4 to step S5, the determination unit 146 sets the wet flag to 1. For example, as shown in Fig. 7D, at time t4, the wet flag is set to 1. When step S5 ends, the process proceeds to step S6.

[0075] When the process proceeds to step S6 from step S5 or step S8 described below, the control unit 142 determines whether or not there is an instruction to stop operation of the fuel cell system 10. The driver of the vehicle turns off an ignition switch (also called a power switch) (not shown) to stop operation of the vehicle. When an off signal accompanying the ignition switch turning off is acquired by the acquisition unit 140, the control unit 142 determines that there is an instruction to stop operation of the fuel cell system 10. When there is an instruction to stop operation of the fuel cell system 10 (step S6: YES), the series of processes shown in FIG. 5 ends. On the other hand, when there is no instruction to stop operation of the fuel cell system 10 (step S6: NO), the process returns to step S1.

[0076] When the process proceeds from step S1 to step S7, the timing unit 144 resets the timer. For example, as shown in Fig. 7C, the timer is reset between time t0 and time t1 and between time t2 and time t3. When step S7 ends, the process proceeds to step S8.

[0077] In step S8, the control unit 142 sets the wet flag to 0. For example, as shown in Fig. 7D, the wet flag is set to 0 between time t0 and time t4. When step S8 ends, the process proceeds to step S6.

[0078] [3-2 Wastewater treatment performed during power generation shutdown] Fig. 8 is a flowchart of the drainage process executed during power generation during shutdown. The series of processes shown in Fig. 8 are executed after a YES determination is made in the process of step S6 shown in Fig. 5. In the drainage process described below, it is possible to switch from the first drainage mode to the second drainage mode during drainage control.

[0079] In step S11, the timing unit 144 sets a drainage time for executing drainage control. Here, the timing unit 144 sets the drainage time to the drainage set time stored in the memory unit 138. When step S11 ends, the process proceeds to step S12.

[0080] In step S12, the timing unit 144 starts timing using a timer. That is, the timing unit 144 starts timing the execution time of the drainage control. When step S12 ends, the process proceeds to step S13.

[0081] In step S13, the determination unit 146 determines whether the fuel cell stack 12 is in a wet state based on the wet flag set in the process shown in Fig. 5. If the wet flag is set to 1 (step S13:1), the process proceeds to step S14. That is, if the fuel cell stack 12 is in a wet state, the process proceeds to step S14. On the other hand, if the wet flag is 0 If it is set (step S13:0), the process proceeds to step S19. That is, if the fuel cell stack 12 is not in a wet state, the process proceeds to step S19.

[0082] When the process moves from step S13 to step S14, or when the process moves from step S16 (described later) to step S14, the control unit 142 executes drainage in a first drainage mode. In the first drainage mode, the control unit 142 controls the operation of the compressor 112 so that the flow rate of the oxidant gas discharged from the compressor 112 becomes a first flow rate. As a result, the oxidant gas at the first flow rate is supplied to the fuel cell stack 12 and the oxidant gas discharge channel 108. In this case, a relatively large flow rate of oxidant gas is supplied to the fuel cell stack 12 and the oxidant gas discharge channel 108. By supplying a large amount of oxidant gas, water remaining in the fuel cell stack 12 and the oxidant gas discharge channel 108 is sufficiently drained. Note that, in the first drainage mode, the control unit 142 controls the rotation speed of the pump 126 to the first rotation speed. When step S14 ends, the process moves to step S15.

[0083] In step S15, the control unit 142 compares the time measured by the timer (first execution time) with the drainage time. If the measured time is equal to or greater than the drainage time (step S15: YES), the drainage control ends. In this case, the control unit 142 stops the compressor 112 and the pump 126. Furthermore, the control unit 142 closes each valve in turn. On the other hand, if the measured time is less than the drainage time (step S15: NO), the process proceeds to step S16.

[0084] When the process proceeds from step S15 to step S16, the determination unit 146 determines whether the fuel cell stack 12 is in a wet state. For example, the determination unit 146 may make the wet state determination based on a wet state determination map 150. When using the wet state determination map 150, the determination unit 146 determines that the fuel cell stack 12 is in a wet state when a combination of a current instruction value (predetermined value) and a temperature value of the cooling medium is within a region of an expected wet state. Alternatively, the determination unit 146 may make the wet state determination based on the impedance value of the fuel cell stack 12. The impedance value of the fuel cell stack 12 is measured by the impedance measuring device 148. If the fuel cell stack 12 is in a wet state (step S16: YES), the process returns to step S14. On the other hand, if the fuel cell stack 12 is not in a wet state (step S16: NO), the process proceeds to step S17.

[0085] When the process proceeds from step S16 to step S17, the timing unit 144 calculates the remaining drainage time by subtracting the first execution time, which is the execution time of drainage in the first drainage mode, from the drainage set time stored in the memory unit 138. Furthermore, the timing unit 144 sets the remaining drainage time as the drainage time (second execution time). When step S17 ends, the process proceeds to step S18.

[0086] In step S18, timing unit 144 resets the timer and then restarts timing using the timer. That is, timing unit 144 starts timing the execution time of drainage control in the second drainage mode. When step S18 ends, the process proceeds to step S19.

[0087] When the process moves from step S13, step S18, or step S20 (described later) to step S19, the control unit 142 performs drainage in the second drainage mode. When moving from step S18 to step S19, the control unit 142 switches the drainage mode from the first drainage mode to the second drainage mode. In the second drainage mode, the control unit 142 controls the operation of the compressor 112 so that the flow rate of the oxidant gas discharged from the compressor 112 becomes the second flow rate. As a result, the oxidant gas at the second flow rate is supplied to the fuel cell stack 12 and the oxidant gas discharge channel 108. In this case, the oxidant gas is supplied to the fuel cell stack 12 and the oxidant gas discharge channel 108 at a flow rate that is smaller than that in the first drainage mode but larger than that during normal power generation. Because the process switches from drainage in the first drainage mode to drainage in the second drainage mode, the fuel cell stack 12 is appropriately drained, and excessive drying of the fuel cell stack 12 can be prevented. In the second drainage mode, the control unit 142 controls the rotation speed of the pump 126 to a second rotation speed, which is greater than the first rotation speed. After step S19 is completed, the process proceeds to step S20.

[0088] In step S20, the control unit 142 compares the time measured by the timer with the drainage time. If the measured time is equal to or greater than the drainage time (step S20: YES), the drainage control ends. In this case, the control unit 142 stops the compressor 112 and the pump 126. Furthermore, the control unit 142 closes each valve in turn. On the other hand, if the measured time is less than the drainage time (step S20: NO), the process returns to step S19.

[0089] As described above, when the fuel cell stack 12 is in a wet state, the control unit 142 executes drainage in the first drainage mode. When the fuel cell stack 12 is no longer in a wet state before a predetermined drainage time (drainage set time) is reached, the control unit 142 executes drainage in the second drainage mode.

[0090] 8, steps S17 and S18 can be omitted. That is, the timer 144 does not need to calculate the second execution time for executing drainage in the second drainage mode. In this case, the control unit 142 Timer Drainage in the second drainage mode is carried out until the time measured by the method reaches the drainage time set in step S11.

[0091] [4. Effects of the above embodiment] If the fuel cell stack 12 contains too much water, there is a risk that the water will freeze. Also, if the fuel cell stack 12 contains too much water, iron from the metal components will be more likely to dissolve in the water. Water containing iron will deteriorate the electrolyte membrane 36. For these reasons, it is preferable to properly drain water from the fuel cell stack 12 so that the water content in the fuel cell stack 12 does not become too high.

[0092] Increasing the amount of oxidant gas supplied to the fuel cell stack 12 can promote drainage from the fuel cell stack 12. On the other hand, if the fuel cell stack 12 is dried more than necessary, there is a risk that the fuel cell stack 12 will deteriorate.

[0093] In the above embodiment, the control unit 142 performs drainage in the first drainage mode when the fuel cell stack 12 is in a wet state. That is, during power generation during a shutdown, the control unit 142 relatively increases the amount of oxidant gas supplied to the fuel cell stack 12. This can promote drainage from the fuel cell stack 12, particularly from the first bypass stopper convex portion 64, the first feed portions 55a and 55b, the second bypass stopper convex portion 80, and the second feed portions 71a and 71b. On the other hand, the control unit 142 performs drainage control in the second drainage mode when the fuel cell stack 12 is not in a wet state. That is, during power generation during a shutdown, the control unit 142 relatively reduces the amount of oxidant gas supplied to the fuel cell stack 12. According to the above embodiment, it is possible to promote drainage from portions of the fuel cell stack 12 that are difficult to drain. Furthermore, according to the above embodiment, it is possible to perform drainage from the fuel cell stack 12 while preventing the fuel cell stack 12 from drying out excessively. That is, according to the above embodiment, it is possible to appropriately perform drainage from the fuel cell stack 12.

[0094] In the above embodiment, when the fuel cell stack 12 changes from a wet state to a predetermined dry state while the drainage control is being performed, the control unit 142 switches from drainage control in the first drainage mode to drainage control in the second drainage mode. In this way, according to the above embodiment, by switching from drainage control in the first drainage mode to drainage control in the second drainage mode, the fuel cell stack 12 is appropriately drained, and excessive drying of the fuel cell stack 12 can be prevented.

[0095] In the above embodiment, the control unit 142 performs drainage control using a predetermined drainage set time as the drainage time. According to the above embodiment, it is possible to prevent the drainage control from being performed for an unnecessarily long time.

[0096] Drainage control in the first drainage mode increases the power consumption of the compressor 112. In the above embodiment, the control unit 142 sets the rotation speed of the pump 126 during drainage in the first drainage mode to be lower than the rotation speed of the pump 126 during drainage in the second drainage mode. Therefore, according to the above embodiment, an increase in the power consumption of the entire fuel cell system 10 can be suppressed.

[0097] [5 Notes] In addition to the above disclosure, the following additional notes are also disclosed.

[0098] (Appendix 1) The first disclosure relates to a fuel cell system (10) including a fuel cell stack (12) including a plurality of power generation cells (24) that generate power using an oxidant gas and a fuel gas, an oxidant gas supplier (112) that supplies the oxidant gas to the fuel cell stack, a supply path (106) through which the oxidant gas supplied to the fuel cell stack flows, a discharge path (108) through which the oxidant gas discharged from the fuel cell stack flows, a temperature sensor (130) that detects a stack temperature that is the temperature of the fuel cell stack, and a control device (22) that controls the oxidant gas supplier, wherein the control device includes a control unit (142) that performs power generation during shutdown, which continues power generation by the power generation cells after receiving an instruction to stop power generation until a predetermined condition is satisfied, an acquisition unit (140) that acquires the stack temperature before the power generation during shutdown, and a control unit (142) that performs a power generation during shutdown based at least on the stack temperature acquired by the acquisition unit. and a determination unit (146) that determines whether the fuel cell stack is in a wet state, wherein the control unit is capable of selectively performing either drainage in a first drainage mode, in which water accumulating in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate, during the shutdown power generation, or drainage in a second drainage mode, in which water accumulating in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, and when the determination unit determines that the fuel cell stack is in the wet state, the control unit performs drainage in the first drainage mode during the shutdown power generation, and when the determination unit determines that the fuel cell stack is not in the wet state, the control unit performs drainage in the second drainage mode during the shutdown power generation.

[0099] The above configuration can promote drainage from difficult-to-drain areas of the fuel cell stack. Furthermore, the above configuration can prevent excessive drying of the fuel cell stack while draining the water from the fuel cell stack. In other words, the above configuration allows for appropriate drainage of the water from the fuel cell stack.

[0100] (Appendix 2) In the fuel cell system described in Supplementary Note 1, the determination unit may determine whether the fuel cell stack is in the wet state based on the stack temperature and an output current value of the fuel cell stack.

[0101] (Appendix 3) In the fuel cell system described in Appendix 2, the judgment unit may acquire the stack temperature and the output current value before the start of the shutdown power generation, and if the stack temperature is below a predetermined temperature threshold and the output current value is below a predetermined current threshold, judge that the fuel cell stack is in an expected wet state, and if the expected wet state reaches a predetermined time (Cth) before the start of the shutdown power generation, judge that the fuel cell stack is in the wet state.

[0102] (Appendix 4) In the fuel cell system described in Supplementary Note 1, the power generating cell may include a structure (26) including an electrolyte membrane (36), an anode electrode (38), and a cathode electrode (40), and a pair of separators (28, 30) sandwiching the structure, and each of the separators may include a reactant gas flow path (50, 66) through which the oxidant gas or the fuel gas flows, a seal portion (62, 78) surrounding the reactant gas flow path, and a bypass suppression portion (64, 80) formed between a flow path width direction end portion (52a, 68a) of the reactant gas flow path and the seal portion, and suppressing bypass of the oxidant gas or the fuel gas.

[0103] The water remaining in the bypass suppression section is difficult to drain at the normal flow rate of the oxidant gas during power generation during shutdown (the second flow rate of the oxidant gas in the second drainage mode). On the other hand, the first flow rate of the oxidant gas in the first drainage mode can promote drainage from the bypass suppression section.

[0104] (Appendix 5) In the fuel cell system described in Appendix 1, the judgment unit may further determine whether the fuel cell stack is in the wet state during drainage in the first drainage mode, and if the judgment unit determines that the fuel cell stack is no longer in the wet state during drainage in the first drainage mode, the control unit may switch from drainage in the first drainage mode to drainage in the second drainage mode.

[0105] According to the above configuration, by switching from drainage control in the first drainage mode to drainage control in the second drainage mode, the fuel cell stack is drained appropriately, and excessive drying of the fuel cell stack can be prevented. Furthermore, even when the fuel cell stack is no longer in a wet state (i.e., in a predetermined dry state), drainage in the second drainage mode can be performed to drain liquid water accumulated in an exhaust device (e.g., a second sealing valve) provided in the exhaust path. This prevents the fuel cell system from being unable to generate electricity at startup due to liquid water accumulated in the exhaust device freezing when the system is shut down.

[0106] (Appendix 6) In the fuel cell system described in Appendix 5, the control unit may measure a first execution time, which is the execution time of drainage in the first drainage mode, determine a second execution time, which is the execution time of drainage in the second drainage mode, based on the first execution time, and perform drainage in the second drainage mode for the second execution time.

[0107] (Appendix 7) In the fuel cell system described in Appendix 5, the control unit may measure a first execution time, which is the execution time of drainage in the first drainage mode, and determine a second execution time, which is the execution time of drainage in the second drainage mode, by subtracting the first execution time from a predetermined drainage time, and perform drainage in the second drainage mode for the second execution time.

[0108] (Appendix 8) In the fuel cell system described in any one of Appendices 1 to 7, a refrigerant supply pump (126) that supplies a cooling medium to the fuel cell stack may be provided, and the control device may set the rotation speed of the refrigerant supply pump when performing drainage in the first drainage mode to be lower than the rotation speed of the refrigerant supply pump when performing drainage in the second drainage mode.

[0109] According to the above configuration, it is possible to suppress an increase in power consumption of the entire fuel cell system.

[0110] (Appendix 9) The second disclosure is a control method for a fuel cell system including a fuel cell stack having a plurality of power generation cells that generate power using an oxidant gas and a fuel gas, an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack, a supply path through which the oxidant gas supplied to the fuel cell stack flows, a discharge path through which the oxidant gas discharged from the fuel cell stack flows, a temperature sensor that detects a stack temperature that is the temperature of the fuel cell stack, and a control device that controls the oxidant gas supplier, wherein the control device performs stoppage power generation in which power generation by the power generation cells is continued from when a command to stop power generation is received until a predetermined condition is satisfied, acquires the stack temperature before the stoppage power generation, and determines a temperature of the power generation cells based at least on the acquired stack temperature before the stoppage power generation. The system is capable of determining whether the fuel cell stack is in a wet state, and selectively performing either a first drainage mode drainage in which water accumulating in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate during the shutdown power generation, or a second drainage mode drainage in which water accumulating in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate.If it is determined that the fuel cell stack is in the wet state, drainage in the first drainage mode is performed during the shutdown power generation, and if it is determined that the fuel cell stack is not in the wet state, drainage in the second drainage mode is performed during the shutdown power generation.

[0111] The above configuration can promote drainage from difficult-to-drain areas of the fuel cell stack. Furthermore, the above configuration can prevent excessive drying of the fuel cell stack while draining the water from the fuel cell stack. In other words, the above configuration allows for appropriate drainage of the water from the fuel cell stack.

[0112] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0113] 10...Fuel cell system 12...Fuel cell stack 22...Control device 24...Power generation cell 26...Electrolyte membrane / electrode structure (structure) 28...First separator (separator) 30...Second separator (separator) 36...electrolyte membrane 38...anode electrode 40...Cathode electrode 50...oxidant gas flow path (reactant gas flow path) 52a... First end flow path protrusion (end in the flow path width direction) 62...First flow path seal portion (seal portion) 64...First bypass stopper convex portion (bypass suppression portion) 66...Fuel gas flow path (reactant gas flow path) 68a... second end flow passage protrusion (end in the width direction of the flow passage) 78...Second flow path seal portion (seal portion) 80...Second bypass stopper convex portion (bypass suppression portion) 106...oxidant gas supply channel (supply channel) 108...Oxidant gas exhaust path (exhaust path) 112...Compressor (oxidant gas supply device) 126... Pump (refrigerant supply pump) 130... Temperature sensor 140... Acquisition unit 142... Control unit 146…Judgment section

Claims

1. a fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; A fuel cell system comprising: The control device a control unit that performs power generation during shutdown, which continues power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is satisfied; an acquisition unit that acquires the stack temperature before the power generation is stopped; a determination unit that determines whether the fuel cell stack is in a wet state based at least on the stack temperature acquired by the acquisition unit, the control unit is capable of selectively performing, during the power generation during shutdown, either drainage in a first drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate, or drainage in a second drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, When the determination unit determines that the fuel cell stack is in the wet state, the control unit executes drainage in the first drainage mode during the power generation during shutdown, When the determination unit determines that the fuel cell stack is not in the wet state, the control unit executes drainage in the second drainage mode during the power generation during shutdown, The determination unit Before the start of the shutdown power generation, the stack temperature and the output current value of the fuel cell stack are acquired; A fuel cell system that determines that the fuel cell stack is in an expected wet state when the stack temperature is below a predetermined temperature threshold and the output current value is below a predetermined current threshold, and determines that the fuel cell stack is in the expected wet state when the expected wet state reaches a predetermined time before the start of the shutdown power generation.

2. A fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; A fuel cell system comprising: The control device a control unit that performs power generation during shutdown, which continues power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is satisfied; an acquisition unit that acquires the stack temperature before the power generation is stopped; a determination unit that determines whether the fuel cell stack is in a wet state based at least on the stack temperature acquired by the acquisition unit, the control unit is capable of selectively performing, during the power generation during shutdown, either drainage in a first drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate, or drainage in a second drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, When the determination unit determines that the fuel cell stack is in the wet state, the control unit executes drainage in the first drainage mode during the power generation during shutdown, When the determination unit determines that the fuel cell stack is not in the wet state, the control unit executes drainage in the second drainage mode during the power generation during shutdown, the determination unit further determines whether the fuel cell stack is in the wet state during the water discharge in the first water discharge mode; The control unit measuring a first execution time, which is the execution time of drainage in the first drainage mode; When the determination unit determines that the fuel cell stack is no longer in the wet state during drainage in the first drainage mode, the drainage mode is switched from the first drainage mode to the second drainage mode, and determining a second execution time, which is the execution time of drainage in the second drainage mode, by subtracting the first execution time from a preset drainage time; The fuel cell system performs drainage in the second drainage mode for the second execution time.

3. A fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; A fuel cell system comprising: a coolant supply pump for supplying a coolant to the fuel cell stack; The control device a control unit that performs power generation during shutdown, which continues power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is satisfied; an acquisition unit that acquires the stack temperature before the power generation is stopped; a determination unit that determines whether the fuel cell stack is in a wet state based at least on the stack temperature acquired by the acquisition unit, the control unit is capable of selectively performing, during the power generation during shutdown, either drainage in a first drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a first flow rate, or drainage in a second drainage mode in which water remaining in the fuel cell stack is drained by supplying the oxidant gas from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, When the determination unit determines that the fuel cell stack is in the wet state, the control unit executes drainage in the first drainage mode during the power generation during shutdown, When the determination unit determines that the fuel cell stack is not in the wet state, the control unit executes drainage in the second drainage mode during the power generation during shutdown, a rotation speed of the coolant supply pump when draining in the first drainage mode is set to be lower than a rotation speed of the coolant supply pump when draining in the second drainage mode.

4. The fuel cell system according to any one of claims 1 to 3, The power generating cell is a structure including an electrolyte membrane, an anode electrode, and a cathode electrode; a pair of separators sandwiching the structure; Equipped with Each of the separators comprises: a reaction gas flow path through which the oxidant gas or the fuel gas flows; a seal portion surrounding the reaction gas flow path; a bypass suppression portion formed between the seal portion and an end portion in a flow path width direction of the reactant gas flow path, the bypass suppression portion suppressing bypass of the oxidant gas or the fuel gas; A fuel cell system comprising:

5. a fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; A control method for a fuel cell system comprising: The control device performing power generation during shutdown by continuing power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is met; The stack temperature before the power generation is stopped is acquired; determining whether the fuel cell stack is in a wet state based at least on the acquired stack temperature before the shutdown power generation; During the power generation during shutdown, it is possible to selectively perform either drainage in a first drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a first flow rate, thereby draining water remaining in the fuel cell stack, or drainage in a second drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, thereby draining water remaining in the fuel cell stack, When it is determined that the fuel cell stack is in the wet state, drainage is performed in the first drainage mode during the power generation during the shutdown period; If it is determined that the fuel cell stack is not in the wet state, drainage is performed in the second drainage mode during the power generation during shutdown; Before the start of the shutdown power generation, the stack temperature and the output current value of the fuel cell stack are acquired; When the stack temperature is less than a predetermined temperature threshold and the output current value is less than a predetermined current threshold, the fuel cell stack is determined to be in an expected wet state, and when the expected wet state has lasted for a predetermined time before the start of the shutdown power generation, the fuel cell stack is determined to be in the expected wet state. A method for controlling a fuel cell system.

6. A fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; A control method for a fuel cell system comprising: The control device performing power generation during shutdown by continuing power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is met; The stack temperature before the power generation is stopped is acquired; determining whether the fuel cell stack is in a wet state based at least on the acquired stack temperature before the shutdown power generation; During the power generation during shutdown, it is possible to selectively perform either drainage in a first drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a first flow rate, thereby draining water remaining in the fuel cell stack, or drainage in a second drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, thereby draining water remaining in the fuel cell stack, When it is determined that the fuel cell stack is in the wet state, drainage is performed in the first drainage mode during the power generation during the shutdown period; If it is determined that the fuel cell stack is not in the wet state, drainage is performed in the second drainage mode during the power generation during shutdown; Further determining whether the fuel cell stack is in the wet state during the draining in the first draining mode; measuring a first execution time, which is the execution time of drainage in the first drainage mode; When it is determined that the fuel cell stack is no longer in the wet state during the water discharge in the first water discharge mode, the water discharge in the first water discharge mode is switched to the water discharge in the second water discharge mode, and determining a second execution time, which is the execution time of drainage in the second drainage mode, by subtracting the first execution time from a preset drainage time; A control method for a fuel cell system, wherein drainage is performed in the second drainage mode for the second execution time.

7. A fuel cell stack including a plurality of power generation cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas supplier that supplies the oxidant gas to the fuel cell stack; a supply path through which the oxidant gas supplied to the fuel cell stack flows; an exhaust passage through which the oxidant gas discharged from the fuel cell stack flows; a temperature sensor for detecting a stack temperature, which is the temperature of the fuel cell stack; a control device for controlling the oxidant gas supply device; a coolant supply pump for supplying a coolant to the fuel cell stack; A control method for a fuel cell system comprising: The control device performing power generation during shutdown by continuing power generation by the power generation cell after receiving an instruction to stop power generation until a predetermined condition is met; The stack temperature before the power generation is stopped is acquired; determining whether the fuel cell stack is in a wet state based at least on the acquired stack temperature before the shutdown power generation; During the power generation during shutdown, it is possible to selectively perform either drainage in a first drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a first flow rate, thereby draining water remaining in the fuel cell stack, or drainage in a second drainage mode in which the oxidant gas is supplied from the oxidant gas supplier to the fuel cell stack at a second flow rate that is less than the first flow rate, thereby draining water remaining in the fuel cell stack, When it is determined that the fuel cell stack is in the wet state, drainage is performed in the first drainage mode during the power generation during the shutdown period; If it is determined that the fuel cell stack is not in the wet state, drainage is performed in the second drainage mode during the power generation during shutdown; A control method for a fuel cell system, comprising: setting a rotation speed of the coolant supply pump when draining in the first drainage mode to be lower than a rotation speed of the coolant supply pump when draining in the second drainage mode.

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