Fuel cell system

Abstract

To appropriately generate low-efficiency electricity while meeting dilution requirements. [Solution] The fuel cell system 10 includes a fuel cell stack 12 that generates electricity, a cathode supply passage 62 that supplies cathode gas to the fuel cell stack 12, a cathode discharge passage 64 that discharges cathode off gas discharged from the fuel cell stack 12, a first valve 74 provided in the cathode supply passage 62, a second valve 76 provided in the cathode discharge passage 64, a cathode bypass passage 66 that bypasses the fuel cell stack 12 and connects the cathode supply passage 62 and the cathode discharge passage 64, a third valve 78 provided in the cathode bypass passage 66, and a control unit 911 that opens the first valve 74 and the third valve 78 during the first power generation when the fuel cell stack 12 generates electricity during warm-up, and controls the opening degree of the second valve 76 to be more closed than the opening degree during the second power generation when the fuel cell stack 12 generates electricity after warm-up is complete.

Description

Technical Field

[0001] The present invention relates to a fuel cell system.

Background Art

[0002] There is known a technique of increasing power loss to raise the temperature of a fuel cell (warming up) by performing an operation with low power generation efficiency by restricting the amount of cathode gas supplied to a fuel cell stack (see Patent Document [1]).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, technological development related to fuel cells that contribute to energy efficiency has been carried out. As a technology related to this type of fuel cell, warming up may be performed by causing the fuel cell stack to generate electricity with deliberately low power generation efficiency (low efficiency). Since warming up involves power generation, there are cases where warming up cannot be performed depending on the charge state of the secondary battery or the state of the waste power-consuming auxiliary machine. Therefore, conventionally, even in a scene where warming up is restricted, it is required to perform warming up as much as possible.

Means for Solving the Problems

[0005] A fuel cell system according to one aspect of the present invention comprises a fuel cell stack that generates electricity using anode gas and cathode gas; a cathode supply passage that supplies cathode gas to the fuel cell stack; a cathode discharge passage that discharges cathode-off gas discharged from the fuel cell stack; a first valve provided in the cathode supply passage; a second valve provided in the cathode discharge passage; a cathode bypass passage that bypasses the fuel cell stack and connects the cathode supply passage and the cathode discharge passage; a third valve provided in the cathode bypass passage; and a control unit that, during a first power generation operation in which the fuel cell stack generates electricity during warm-up, opens the first and third valves and controls the opening of the second valve to be more closed than the opening during a second power generation operation in which the fuel cell stack generates electricity after warm-up is complete. [Effects of the Invention]

[0006] According to the present invention, it becomes possible to increase the opportunities for warming up the engine compared to conventional methods. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of a fuel cell system according to an embodiment of the present invention. [Figure 2] A diagram illustrating part of the control device configuration. [Figure 3] A flowchart illustrating an example of the process for setting the power generation mode. [Modes for carrying out the invention]

[0008] Embodiments of the invention will be described below with reference to the drawings. <Fuel cell system configuration> Figure 1 is a schematic diagram of the fuel cell system 10 according to the present invention. The fuel cell system 10 is mounted on a vehicle (fuel cell vehicle). Alternatively, the fuel cell system 10 may be mounted on a ship, aircraft, robot, etc. The fuel cell system 10 includes a fuel cell stack 12, a hydrogen tank 14, an anode system 16, a cathode system 18, a cooling system 20, and a control device 900. The output (power) of the fuel cell stack 12 is boosted to the required voltage by a voltage converter 200 and supplied to a battery 300 as a secondary battery or to a load 400 such as a motor. The battery 300 is composed of, for example, a lithium-ion battery. In this embodiment, as an example, regenerative power from the load 400 and FC power obtained by the power generation operation of the fuel cell stack 12 are stored (charged) in the battery 300, and the battery 300 is discharged in order to drive the vehicle and operate a predetermined group of auxiliary equipment.

[0009] The fuel cell stack 12 has a plurality of power generation cells 22 stacked in one direction. Each power generation cell 22 has an electrolyte membrane / electrode structure 24 (also simply called an electrode structure 24) and a pair of separators 26, 28. The pair of separators 26, 28 sandwich the electrode structure 24.

[0010] The electrode structure 24 comprises a solid polymer electrolyte membrane (also simply called an electrolyte membrane 30), an anode electrode 32, and a cathode electrode 34. The electrolyte membrane 30 is, for example, a thin film of perfluorosulfonic acid containing water. The anode electrode 32 and the cathode electrode 34 sandwich the electrolyte membrane 30. The anode electrode 32 and the cathode electrode 34 have a gas diffusion layer made of carbon paper or the like. An electrode catalyst layer is formed by uniformly coating the surface of the gas diffusion layer with porous carbon particles. A platinum alloy is supported on the surface of the porous carbon particles. The electrode catalyst layer is formed on both sides of the electrolyte membrane 30.

[0011] On the surface of the separator 26 facing the electrode structure 24, an anode channel 36 is formed. The anode channel 36 is connected to the anode supply channel 40 via the anode inlet 17A. The anode channel 36 is connected to the anode discharge channel 42 via the anode outlet 17B. On the surface of the separator 28 facing the electrode structure 24, a cathode channel 38 is formed. The cathode channel 38 is connected to the cathode supply channel 62 via the cathode inlet 19A. The cathode channel 38 is connected to the cathode discharge channel 64 via the cathode outlet 19B. The supply channel may also be called the supply path, and the discharge channel may also be called the discharge path.

[0012] Anode gas (hydrogen) is supplied to the anode electrode 32. At the anode electrode 32, hydrogen ions and electrons are generated from hydrogen molecules by an electrode reaction mediated by a catalyst. The hydrogen ions permeate the electrolyte membrane 30 and move to the cathode electrode 34. The electrons move in the following order: anode electrode 32, negative electrode terminal of fuel cell stack 12 (not shown), voltage converter 200, positive electrode terminal of fuel cell stack 12 (not shown), and cathode electrode 34. At the cathode electrode 34, water is produced by a reaction between hydrogen ions and electrons and oxygen contained in the supplied air, mediated by the catalyst.

[0013] The anode system 16 has components for supplying anode gas to the anode electrode 32 and components for discharging anode off-gas from the anode electrode 32. The anode system 16 has an anode supply channel 40, an anode discharge channel 42, a circulation channel 44, and a drain channel 46. The anode system 16 also has an injector 50, an ejector 52, a gas-liquid separator 54, and a drain valve 56. The anode discharge channel 42 and the drain channel 46 are sometimes collectively referred to as the anode discharge channel.

[0014] The anode supply channel 40 connects the outlet of the hydrogen tank 14 to the anode inlet 17A. The anode supply channel 40 is equipped with an injector 50, an ejector 52, and a pressure sensor 93. The ejector 52 is positioned closer to the anode inlet 17A than the injector 50. The pressure sensor 93 is positioned closer to the anode inlet 17A than the ejector 52. The pressure sensor 93 detects the pressure of the anode gas and sends a detection signal to the control device 900.

[0015] The anode discharge channel 42 connects the anode outlet 17B to the intake port of the gas-liquid separator 54. The circulation channel 44 connects the exhaust port of the gas-liquid separator 54 to the ejector 52. The drain channel 46 connects the drain port of the gas-liquid separator 54 to the inlet of the diluent 60. A drain valve 56 is provided in the drain channel 46.

[0016] The cathode system 18 has components for supplying cathode gas to the cathode electrode 34 and components for discharging cathode off gas from the cathode electrode 34. The cathode system 18 has a cathode supply channel 62, a cathode discharge channel 64, and a bypass channel 66. The cathode system 18 also has a compressor 68 as a cathode gas supply device, a humidifier 70, a sealing valve 74 as a first valve, a back pressure valve 76 as a second valve, and a bypass valve 78 as a third valve. The bypass channel may also be called a cathode bypass channel.

[0017] The cathode supply channel 62 communicates an air intake port (not shown) with the cathode inlet 19A. The cathode supply channel 62 is provided with a compressor 68, a shutoff valve 74, and the channel 72A of a humidifier 70. The upstream portion of the cathode supply channel 62 from the humidifier 70 is defined as the cathode supply channel 62A. The downstream portion of the cathode supply channel 62 from the humidifier 70 is defined as the cathode supply channel 62B. The cathode supply channel 62A is provided with a pressure sensor 95, an air flow sensor 98, a compressor 68, and a shutoff valve 74. The shutoff valve 74 is arranged closer to the humidifier 70 than the compressor 68. The pressure sensor 95 and the air flow sensor 98 are arranged on the air intake port (not shown) side of the compressor 68. The pressure sensor 95 detects the pressure of the intake air (atmospheric air) and sends a detection signal to the control device 900. The pressure sensor 95 also functions as an atmospheric pressure sensor outside the vehicle. The air flow sensor 98 detects the supply flow rate of the cathode gas (which may also be called the compressor supply flow rate) and sends a detection signal to the control device 900. The cathode supply channel 62B is provided with an air flow sensor 99. The air flow sensor 99 detects the flow rate of the cathode gas supplied to the fuel cell stack 12 (which may also be called the stack supply flow rate) and sends a detection signal to the control device 900. The stack supply flow rate corresponds to the flow rate obtained by subtracting the flow rate of the cathode gas flowing through the bypass channel 66 (which may also be called the bypass flow rate) from the compressor supply flow rate.

[0018] The cathode discharge channel 64 communicates the cathode outlet 19B with the inlet of the diluter 60. The cathode discharge channel 64 is provided with the channel 72B of a humidifier 70 and a back pressure valve 76. The upstream portion of the cathode discharge channel 64 from the humidifier 70 is defined as the cathode discharge channel 64A. The downstream portion of the cathode supply channel 62 from the humidifier 70 is defined as the cathode discharge channel 64B. The back pressure valve 76 is provided in the cathode discharge channel 64B.

[0019] The discharge pipe 100 is composed of, for example, a hollow pipe with a length of about 1 m. The inlet 100A of the discharge pipe 100 is connected to the outlet of the diluter 60. The outlet 100C of the discharge pipe 100 is located, for example, under the floor at approximately the center of the vehicle. By providing the discharge pipe 100, the gas diluted by the diluter 60 (the combined gas formed by the confluence of the cathode off-gas flowing through the cathode discharge channel 64B and the anode off-gas flowing through the anode discharge channel 42 and the drain channel 46) is discharged to the outside (into the atmosphere) in a space away from the vehicle user.

[0020] The bypass channel 66 connects the cathode supply channel 62A and the cathode discharge channel 64B. For example, the bypass channel 66 connects a portion between the compressor 68 and the shut-off valve 74 in the cathode supply channel 62A and a portion downstream of the back-pressure valve 76 in the cathode discharge channel 64B. A bypass valve 78 is provided in the bypass channel 66.

[0021] The cooling system 20 has each component for supplying a refrigerant to the fuel cell stack 12 and each component for discharging the refrigerant from the fuel cell stack 12. The cooling system 20 has a refrigerant supply channel 84 and a refrigerant discharge channel 86. Further, the cooling system 20 has a refrigerant pump 88, a radiator 90, and a temperature sensor 92.

[0022] Inside the fuel cell stack 12, a refrigerant flow path (not shown) for cooling the fuel cell stack 12 is formed. The refrigerant supply channel 84 connects the outlet of the radiator 90 and the inlet of the refrigerant flow path. A refrigerant pump 88 is provided in the refrigerant supply channel 84. The refrigerant discharge channel 86 connects the outlet of the refrigerant flow path and the inlet of the radiator 90. A temperature sensor 92 is provided in the refrigerant discharge channel 86. The temperature sensor 92 detects the temperature of the refrigerant discharged from the fuel cell stack 12 and sends a detection signal to the control device 900.

[0023] The control device 900 is a computer (for example, a vehicle's ECU). The control device 900 includes a control unit 911, a storage unit 912, a first supply flow rate calculation unit 913, a second supply flow rate calculation unit 914, a selection unit 915, a cathode compressor control unit 916, a bypass valve opening degree calculation unit 917, and a bypass valve control unit 918. The control unit 911 has a processing circuit. The processing circuit may be a processor such as a CPU. The processing circuit may be an integrated circuit such as an ASIC or FPGA. The processor can perform various processes by executing a program stored in the storage unit 912. At least some of the processes may be performed by an electronic circuit including discrete devices.

[0024] The control unit 911 controls the operation of the fuel cell system 10. For example, the control unit 911 receives detection signals from various sensors provided in the fuel cell system 10. Based on each detection signal, the control unit 911 outputs control signals to control each of the valves, injectors 50, compressors 68, refrigerant pumps 88, etc. Each of the valves, injectors 50, compressors 68, refrigerant pumps 88, etc. operates according to the control signals.

[0025] The storage unit 912 has volatile memory and non-volatile memory. Examples of volatile memory include RAM. The volatile memory is used as the working memory of the processor. The volatile memory temporarily stores data necessary for processing or calculation. Examples of non-volatile memory include ROM and flash memory. The non-volatile memory is used as memory for data storage. The non-volatile memory stores programs, tables, maps, etc. At least a part of the storage unit 912 may be provided in a processor, integrated circuit, etc. as described above.

[0026] Figure 2 is a diagram illustrating the first supply flow rate calculation unit 913, the second supply flow rate calculation unit 914, the selection unit 915, the cathode compressor control unit 916, the bypass valve opening degree calculation unit 917, and the bypass valve control unit 918, which are all part of the control device 900. The supply flow rate first calculation unit 913 receives target output information from the control unit 911, indicating the target output (which may also be called target power generation or target electricity) of the fuel cell stack 12. Based on the target output, the supply flow rate first calculation unit 913 calculates a first target flow rate (which may also be called a first discharge rate). The first target flow rate is the target value of the cathode gas supply flow rate to the fuel cell stack 12, which is used to ensure the oxygen partial pressure necessary for the electrode reaction at the cathode electrode 34 of each power generation cell 22 when the target output is extracted from the fuel cell stack 12. The first target flow rate increases or decreases according to the target output when a power generation request is made. That is, the cathode gas supply flow rate based on a power generation request is higher when the target output is larger than when the target output is smaller.

[0027] The second supply flow rate calculation unit 914 receives the target output, anode pressure information (detected by pressure sensor 93) indicating the pressure of the anode gas, atmospheric pressure information (detected by pressure sensor 95) indicating atmospheric pressure, and stack temperature information (detected by temperature sensor 92) indicating the stack temperature. Based on the input values ​​of each of these pieces of information, the second supply flow rate calculation unit 914 calculates a second target flow rate (which may also be called a second discharge rate). The second target flow rate is the target value of the cathode gas supply flow rate to the diluent 60 necessary to dilute the hydrogen concentration of the exhaust gas discharged from the outlet 100C of the discharge pipe 100 to below the combustible concentration. The second target flow rate increases or decreases depending on the hydrogen concentration of the anode off-gas when a dilution request is made. That is, the cathode gas supply flow rate based on a dilution request is higher when the hydrogen concentration is high compared to when the hydrogen concentration is low.

[0028] The selection unit 915 receives a signal indicating the first target flow rate and a signal indicating the second target flow rate. Normally, based on a command from the control unit 911, the selection unit 915 selects the larger of the first target flow rate based on the target output and the second target flow rate based on the dilution request as the target compressor supply flow rate. Furthermore, based on a command from the control unit 911, the selection unit 915 selects a second target flow rate based on the dilution request as the target compressor supply flow rate when generating power for warm-up.

[0029] The cathode compressor control unit 916 receives a signal indicating the compressor supply flow rate (detected by the airflow sensor 98) and a signal indicating the target compressor supply flow rate. The cathode compressor control unit 916 calculates a torque command value for the compressor 68 based on the deviation between the compressor supply flow rate and the target compressor supply flow rate, and controls the compressor 68 according to this torque command value. As a result, the compressor supply flow rate is controlled to the target compressor supply flow rate.

[0030] The bypass valve opening calculation unit 917 receives stack supply flow rate information (detected by the airflow sensor 99) and a signal indicating the first target flow rate. Based on the deviation between the stack supply flow rate and the first target flow rate, the bypass valve opening calculation unit 917 calculates the opening degree of the bypass valve 78 required to bring the stack supply flow rate to the first target flow rate, which is called the target bypass valve opening degree.

[0031] When the selection unit 915 selects the first target flow rate as the target compressor supply flow rate, the compressor 68 is controlled so that the compressor supply flow rate becomes the first target flow rate. Therefore, there is no need to bypass the cathode gas discharged from the compressor 68, and the target bypass valve opening is set to fully closed.

[0032] On the other hand, when the selection unit 915 selects the second target flow rate as the target compressor supply flow rate, the compressor supply flow rate becomes greater than the first target flow rate in order to dilute the hydrogen discharged into the drain channel 46. Therefore, the bypass valve opening calculation unit 917 sets the target bypass valve opening so that the excess amount (second target flow rate - first target flow rate) flows into the bypass channel 66.

[0033] The bypass valve control unit 918 receives a signal indicating the target bypass valve opening. The bypass valve control unit 918 controls the opening of the bypass valve 78 to the target bypass valve opening.

[0034] <Fluid flow> 1. Anode System The fluid flow in the anode system 16 in Figure 1 will be explained. The injector 50 injects anode gas (hydrogen) from the hydrogen tank 14 downstream of the anode supply channel 40. The anode gas injected from the injector 50 flows through the anode supply channel 40 and is supplied to the anode channel 36. The anode gas flows through the anode channel 36 and is discharged from the anode outlet 17B as anode off gas. The anode off gas contains hydrogen that did not react with oxygen, nitrogen in the cathode gas that has permeated the electrolyte membrane 30, and water produced by the reaction between oxygen and hydrogen.

[0035] The anode off gas flows through the anode discharge channel 42 and is supplied to the gas-liquid separator 54. The gas-liquid separator 54 separates the anode off gas into a gaseous component (anode off gas) and a liquid component (water). The anode off gas discharged from the gas-liquid separator 54 flows through the circulation channel 44 and is supplied to the ejector 52. In the ejector 52, the anode off gas and the anode gas injected from the injector 50 merge.

[0036] The water separated in the gas-liquid separator 54 is temporarily stored at the bottom of the gas-liquid separator 54. With the drain valve 56 open, the water stored in the gas-liquid separator 54 flows through the drain channel 46 and is discharged to the diluent 60. When the drain valve 56 opens after the water in the gas-liquid separator 54 has been depleted, the anode-off gas from the gas-liquid separator 54 flows through the drain channel 46 and is discharged to the diluent 60.

[0037] 2. Cathode System The fluid flow in the cathode system 18 will be described. The compressor 68 discharges cathode gas (air) drawn in from outside the vehicle downstream of the cathode supply passage 62. With the sealing valve 74 open, the cathode gas discharged from the compressor 68 flows through the cathode supply passage 62 and is supplied to the cathode passage 38. The cathode gas flows through the cathode passage 38 and is discharged from the cathode outlet 19B as cathode-off gas. The cathode-off gas contains the various components contained in the air, as well as water produced by the reaction of oxygen and hydrogen.

[0038] With the back pressure valve 76 open, the cathode-off gas flows through the cathode discharge channel 64 and is discharged to the diluent 60. The cathode-off gas contains moisture. In the humidifier 70, the moisture in the cathode-off gas is used to humidify the cathode gas.

[0039] With the bypass valve 78 open, the cathode gas flows through the bypass channel 66 and the cathode discharge channel 64 and is discharged to the diluent 60. The bypass channel 66 is used to reduce the amount of cathode gas supplied to the fuel cell stack 12.

[0040] <Warm up> In this embodiment, when the fuel cell system 10 is started, if the stack temperature (detected by the temperature sensor 92) has dropped to a predetermined temperature, the control device 900 causes the fuel cell system 10 to perform warm-up power generation (corresponding to the first power generation described later). During warm-up power generation, the flow rate of cathode gas is reduced compared to normal power generation (corresponding to the second power generation described later), causing the fuel cell stack 12 to perform low-efficiency power generation (this may also be called a low-efficiency power generation request), thereby increasing the amount of heat generated compared to normal power generation. For example, the supply flow rate of cathode gas based on the low-efficiency power generation request is set to be smaller than the supply flow rate of cathode gas based on the normal power generation request. Incidentally, in low-efficiency power generation, the concentration of excess hydrogen in the anode off-gas increases, so even when reducing the cathode gas supplied to the fuel cell stack 12, it may be necessary to send the cathode gas required for dilution to the diluent 60 (in other words, not reduce the cathode gas) (this can also be called a dilution request). The following describes the control mechanism that reduces the flow rate of cathode gas supplied to the fuel cell stack 12 in response to low-efficiency power generation requirements, while simultaneously supplying the necessary cathode gas to the diluent 60 in response to dilution requirements.

[0041] (Cathode gas flow rate during normal power generation) The control device 900, using the bypass valve opening calculation unit 917, calculates the target bypass valve opening degree for the opening of the bypass valve 78 in order to bring the stack supply flow rate to the first target flow rate, based on the deviation between the stack supply flow rate and the first target flow rate. Furthermore, the control device 900, using the selection unit 915, selects the larger of the first target flow rate and the second target flow rate as the target compressor supply flow rate.

[0042] When the first target flow rate > the second target flow rate, the selection unit 915 selects the first target flow rate as the target compressor supply flow rate. The cathode compressor control unit 916 controls the compressor 68 so that the compressor supply flow rate becomes the first target flow rate. In this case, the bypass valve opening calculation unit 917 only needs to supply the cathode gas discharged from the compressor 68 to the fuel cell stack 12 without bypassing it, so it sets the target bypass valve opening to fully closed.

[0043] When the first target flow rate < the second target flow rate, the selection unit 915 selects the second target flow rate as the target compressor supply flow rate. The cathode compressor control unit 916 controls the compressor 68 so that the compressor supply flow rate becomes the second target flow rate. In this case, the bypass valve opening calculation unit 917 sets the target bypass valve opening so that the excess cathode gas discharged from the compressor 68 (i.e., second target flow rate - first target flow rate) flows into the bypass flow path 66.

[0044] (Cathode gas flow rate during warm-up power generation) The selection unit 915 selects the second target flow rate as the target compressor supply flow rate during warm-up power generation. The cathode compressor control unit 916 controls the compressor 68 so that the compressor supply flow rate becomes the second target flow rate. In this case, the bypass valve opening calculation unit 917 sets the target bypass valve opening so that the excess cathode gas discharged from the compressor 68 (i.e., second target flow rate - first target flow rate) flows into the bypass flow path 66. Here, even if the bypass valve opening calculation unit 917 were to set the target bypass valve opening to fully open, the flow rate of cathode gas supplied to the fuel cell stack 12 may exceed the first target flow rate due to the structural flow division ratio determined by the inner diameter of the pipelines constituting the cathode supply passage 62 and the bypass passage 66. In other words, the amount of power generated by the fuel cell stack 12 may exceed the target output during warm-up power generation. Therefore, in this embodiment, during warm-up power generation, the back pressure valve 76 is controlled to close based on a command from the control unit 911, thereby controlling the opening of the back pressure valve 76 to be smaller than during normal power generation. This makes it possible to control the flow rate of cathode gas supplied to the fuel cell stack 12 to the first target flow rate. Furthermore, even if the flow rate of cathode gas supplied to the fuel cell stack 12 decreases during warm-up power generation compared to normal power generation, the compressor supply flow rate is controlled to the second target flow rate. Therefore, the total flow rate of cathode gas supplied to the diluent 60 does not decrease, and the dilution requirement is met.

[0045] <Explanation of the flowchart> Figure 3 is a flowchart showing an example of the process of setting the power generation mode, which is executed by the control unit 911 based on a predetermined program. The control unit 911 performs the process shown in Figure 3 when the fuel cell system 10 is started (for example, when the vehicle's ignition switch (not shown) is turned on).

[0046] In step S1, the control unit 911 determines whether or not there is a power generation request from the ECU (not shown) to the fuel cell system 10. If there is a power generation request, the control unit 911 affirms step S1 and proceeds to step S2; if there is no power generation request, it denies step S1 and proceeds to step S3.

[0047] In step S2, the control unit 911 determines whether or not a warm-up request is required. For example, if the stack temperature (detected by the temperature sensor 92) is lower than a predetermined temperature, the control unit 911 determines that a warm-up request is required, affirms step S2, and proceeds to step S4. If the stack temperature is above the predetermined temperature, the control unit 911 determines that there is no warm-up request, negates step S2, and proceeds to step S5. The control unit 911 may also determine whether or not a warm-up request is required based on the temperature of the cathode off-gas flowing through the cathode discharge channel 64 or the temperature of the anode off-gas flowing through the anode discharge channel 42.

[0048] In step S3, the control unit 911 sets the system to not be in power generation mode (which may be called standby mode) and terminates the process shown in Figure 3.

[0049] In step S4, the control unit 911 determines whether the charge state of the battery 300 (which may also be called the battery charge rate) is below a predetermined value. If the SOC is below the predetermined value, the control unit 911 affirms step S4 and proceeds to step S6. If the SOC is not below the predetermined value, the control unit 911 negates step S4 and proceeds to step S7.

[0050] Step S5 is performed only if a warm-up operation is not performed. In step S5, the control unit 911 sets the system to the normal power generation mode and terminates the process shown in Figure 3.

[0051] Step S6 is initiated when the battery 300's charge level has decreased and the engine is being warmed up. In step S6, the control unit 911 sets the engine to the normal low-efficiency power generation mode and terminates the process shown in Figure 3.

[0052] Step S7 is performed when the battery 300 is not charged and the engine is being warmed up. In step S7, the control unit 911 sets the power generation mode to an even lower efficiency mode than the normal low-efficiency power generation mode and terminates the process shown in Figure 3.

[0053] According to the embodiment described above, the following effects and advantages are achieved. (1) The fuel cell system 10 includes a fuel cell stack 12 that generates electricity using anode gas and cathode gas, a cathode supply channel 62 that supplies cathode gas to the fuel cell stack 12, a cathode discharge channel 64 that discharges cathode off gas discharged from the fuel cell stack 12, a first valve 74 provided in the cathode supply channel 62, a second valve 76 provided in the cathode discharge channel 64, a bypass channel 66 that bypasses the fuel cell stack 12 and connects the cathode supply channel 62 and the cathode discharge channel 64, a third valve 78 provided in the bypass channel 66, and a control unit 911 that opens the second valve 76 and the third valve 78 during a first power generation operation in which the fuel cell stack 12 generates electricity during warm-up, and controls the opening degree of the second valve 76 to be more closed than the opening degree during a second power generation operation in which the fuel cell stack 12 generates electricity after warm-up is complete. This configuration allows for more opportunities for warming up than in the conventional system. For example, while maintaining the opening of the second valve 76 and the third valve 78, it becomes possible to reduce the flow rate of cathode gas through the fuel cell stack 12 during the first power generation compared to the second power generation. In other words, by controlling the second valve 76 to the closed side when warming up is required compared to when warming up is not required, it becomes possible to appropriately perform low-efficiency power generation with a lower cathode gas flow rate than in the conventional system. In this way, by achieving a flow division ratio higher than that of the original piping structure during the first power generation phase (warm-up phase), it becomes possible to keep the target output of the fuel cell stack 12 lower.

[0054] (2) The fuel cell system 10 described in (1) above further includes a battery 300 as a rechargeable secondary battery and a control unit 911 as an information acquisition unit that acquires information (e.g., SOC) indicating the charge state of the battery 300, wherein the control unit 911 controls the opening degree of the second valve 76 in multiple stages based on the charge state of the battery 300 during the first power generation. With this configuration, for example, by controlling the opening degree of the second valve 76 in multiple stages based on the State of Charge (SOC) of the battery 300, it becomes possible to control the amount of power generated by the fuel cell stack 12 during the first power generation (warm-up) in multiple stages.

[0055] (3) In the fuel cell system 10 described in (2) above, the control unit 911 controls the opening of the second valve 76 to a second opening greater than the first opening when the SOC is less than a predetermined value during the first power generation, and controls the opening of the second valve 76 to the first opening when the SOC is equal to or greater than the predetermined value. With this configuration, for example, if the State of Charge (SOC) of battery 300 exceeds a predetermined value and the battery's allowable power absorption decreases, in other words, if it becomes difficult for battery 300 to absorb the current generated from the fuel cell stack 12, the opening of the second valve 76 is controlled to the first opening, which is a more closed position, thereby suppressing the amount of power generated. In other words, the first power generation (warm-up) can be performed appropriately so that battery 300 does not become overcharged. As a result, it becomes possible to continue the first power generation for a longer period than if the opening of the second valve 76 were maintained at the second opening.

[0056] (4) In the fuel cell system 10 described in (3) above, the fuel cell stack 12 generates electricity at a lower power generation efficiency than during the second power generation, with the second valve 76 controlled to the first or second opening during the first power generation. With this configuration, the amount of power generated by the fuel cell stack 12 can be suppressed by controlling the opening of the second valve 76 to the first or second opening, and the heat generated during low-efficiency power generation is used for warming up, making it possible to properly prevent overcharging of the battery 300 and warm it up.

[0057] (5) In the fuel cell system 10 described in (4) above, the control unit 911 sets the first opening degree during the first power generation to be smaller than the opening degree set for the second valve during the second power generation, and at least equal to the minimum opening degree that can be set for the second valve. With this configuration, it is possible to perform the first power generation (warm-up) at a lower efficiency than the second power generation, while taking into consideration the durability of the second valve 76.

[0058] (6) The fuel cell system 10 described in (5) above is further provided with a compressor 68 as a cathode gas supply unit that supplies cathode gas to the cathode supply channel 62, and the control unit 911 controls the compressor 68 to discharge cathode gas at the larger of the first discharge amount based on the power generation request and the second discharge amount based on the dilution request during the second power generation, and to discharge cathode gas at the second discharge amount during the first power generation. With this configuration, it is possible to satisfy both the power generation requirement and the dilution requirement while controlling the opening degree of the second valve 76 to either the first or second opening degree. In particular, during the first power generation, when the state of charge of the battery 300 is high and low-efficiency power generation is required, it is possible to perform low-efficiency power generation (satisfying both the power generation requirement and the warm-up requirement) without changing the total amount of air discharged from the compressor 68 (satisfying the dilution requirement).

[0059] The above embodiment can be modified into various forms. Modifications will be described below. (modified version) If step S4 described above is deemed negative, and the State of Charge (SOC) of battery 300 is greater than the predetermined value, and the charge level of battery 300 exceeds a second predetermined value indicating that it is nearly fully charged, the system may be configured not to enter power generation mode and terminate the process shown in Figure 3. This makes it possible to prevent overcharging of battery 300 by continuing to generate power, even if at low efficiency. On the other hand, if the State of Charge (SOC) of battery 300 is greater than the above predetermined value but less than or equal to the second predetermined value, the system proceeds to step S7 and sets to a power generation mode that is even less efficient than the normal low-efficiency power generation mode. By performing warm-up power generation in a power generation mode that is even less efficient than the normal low-efficiency power generation mode, it becomes possible to continue warming up while suppressing the increase in the charge level of battery 300 more gradually.

[0060] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as they do not impair the features of the present invention. [Explanation of symbols]

[0061] 10 Fuel cell system, 12 Fuel cell stack, 36 Anode channel, 38 Cathode channel, 40 Anode supply channel, 42 Anode discharge channel, 46 Drain channel, 56 Drain valve, 60 Diluter, 62 Cathode supply channel, 64, 64A, 64B Cathode discharge channel, 66 Bypass channel, 68 Compressor, 74 Sealing valve (1st valve), 76 Back pressure valve (2nd valve), 78 Bypass valve (3rd valve), 900 Control device, 911 Control unit, 100 Discharge pipe, 300 Battery

Claims

1. A fuel cell stack that generates electricity using anode gas and cathode gas, A cathode supply path for supplying the cathode gas to the fuel cell stack, A cathode discharge channel for discharging cathode off-gas discharged from the fuel cell stack, A first valve provided in the cathode supply path, A second valve provided in the cathode discharge passage, A cathode bypass path that bypasses the fuel cell stack and connects the cathode supply path and the cathode discharge path, A third valve is provided in the cathode bypass path, A control unit that, during the first power generation when the fuel cell stack generates electricity during warm-up, opens the first valve and the third valve, and controls the opening of the second valve to be more closed than the opening during the second power generation when the fuel cell stack generates electricity after the warm-up is complete, A fuel cell system characterized by comprising the following features.

2. In the fuel cell system according to claim 1, A rechargeable secondary battery, The system further includes an information acquisition unit that acquires information indicating the charge state of the secondary battery, The control unit controls the opening degree of the second valve in multiple stages based on the charge state of the secondary battery during the first power generation. A fuel cell system characterized by the following features.

3. In the fuel cell system according to claim 2, The control unit controls the opening of the second valve to a second opening greater than the first opening when the value indicating the charge state is less than a predetermined value during the first power generation, and controls the opening of the second valve to the first opening when the value indicating the charge state is equal to or greater than the predetermined value. A fuel cell system characterized by the following features.

4. In the fuel cell system according to claim 3, The fuel cell stack, during the first power generation, performs power generation with a lower power generation efficiency than during the second power generation, with the second valve controlled to a first or second opening. A fuel cell system characterized by the following features.

5. In the fuel cell system according to claim 4, The control unit sets the first opening degree during the first power generation to be smaller than the opening degree set for the second valve during the second power generation, and at least equal to the minimum opening degree that can be set for the second valve. A fuel cell system characterized by the following features.

6. In the fuel cell system according to claim 5, The system further includes a cathode gas supply unit that supplies the cathode gas to the cathode supply path, The control unit, During the second power generation described above, the cathode gas is discharged at the larger of the first discharge amount based on the power generation request and the second discharge amount based on the dilution request. During the first power generation, the cathode gas supply unit is controlled to discharge the cathode gas at the second discharge volume. A fuel cell system characterized by the following features.

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