Fuel cell system

Abstract

To prevent the sticking of control valves that are only opened in specific situations. [Solution] A fuel cell system 10 including a fuel cell stack 12 that generates electricity using anode gas and cathode gas includes a control device 900 that performs a series of power generation controls including at least start control based on a start instruction, normal power generation control based on a power generation target, and stop control based on a stop instruction; a normally closed type control valve 69 in which a movable valve body abuts against a sealing member of a valve seat in a closed state; and a storage device 912 that stores opening information indicating that the control valve 69, which opens under predetermined conditions, has opened. The control device 900 includes a forced opening process to open the control valve 69 in the stop control if the control valve 69 has not opened before the stop control in the series of power generation controls.

Description

Technical Field

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

Background Art

[0002] There is known a technique for performing drying control such that dry air is supplied to a fuel cell stack at startup under low temperature by opening a bypass flow rate control valve (humidifier bypass valve) provided in a bypass flow path that bypasses a humidifier provided in a cathode flow path for supplying cathode gas 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, for ensuring access to sustainable and advanced energy, technical development related to fuel cells that contribute to energy efficiency improvement has been carried out. In the conventional technology, when the humidifier bypass valve is not opened for a long time, there is a risk that the humidifier bypass valve becomes fixed in a closed state.

Means for Solving the Problems

[0005] One aspect of the present invention is a fuel cell system including a fuel cell stack that generates electricity using anode gas and cathode gas, comprising: a control device that performs a series of power generation controls including at least start control based on a start instruction, normal power generation control based on a power generation target, and stop control based on a stop instruction; a normally closed type control valve in which a movable valve body abuts a sealing member of a valve seat in a closed state; and a storage device that stores opening information indicating that a control valve that opens under predetermined conditions has opened, wherein the control device includes a forced opening process to open the control valve in the stop control if the control valve has not opened before the stop control in the series of power generation controls. [Effects of the Invention]

[0006] According to the present invention, for example, it is possible to prevent a control valve that is only opened in limited situations from becoming stuck in the closed position. [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 the overview of power generation control in a fuel cell system. [Figure 3] A diagram illustrating the flow of the shutdown process. [Figure 4A] A flowchart illustrating an example of a series of power generation control processes executed by the control unit. [Figure 4B] A flowchart explaining the details of the stop control. [Figure 5A] A cross-sectional view illustrating a humidifier bypass valve. [Figure 5B] A perspective view illustrating the main components of the humidifier bypass valve. [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 communicates the outlet of the hydrogen tank 14 with the anode inlet 17A. An injector 50, an ejector 52, and a pressure sensor 93 are provided in the anode supply channel 40. The ejector 52 is disposed closer to the anode inlet 17A than the injector 50. The pressure sensor 93 is disposed on the anode inlet 17A side with respect to 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 communicates the anode outlet 17B with the intake port of the gas-liquid separator 54. The circulation channel 44 communicates the exhaust port of the gas-liquid separator 54 with the ejector 52. The drain channel 46 communicates the drain port of the gas-liquid separator 54 with the inlet of the diluter 60. A drain valve 56 is provided in the drain channel 46.

[0016] The cathode system 18 includes each component for supplying cathode gas to the cathode electrode 34 and each component for discharging cathode off-gas from the cathode electrode 34. The cathode system 18 includes a cathode supply channel 62, a cathode discharge channel 64, a cathode bypass channel 66, and a humidifier bypass channel 63. Further, the cathode system 18 includes a compressor 68 as a cathode gas supply device, a humidifier 70, a shutoff valve (In) 74, a shutoff valve (Out) 76, a cathode bypass valve 78, and a humidifier bypass valve 69. Note that the cathode bypass channel may be referred to as the cathode bypass path, and the humidifier bypass channel may be referred to as the humidifier bypass path. Also, the humidifier bypass valve 69 may be referred to as the control valve. In the fuel cell system 10 according to the embodiment, as will be described in detail later, a forced valve opening process is performed for the purpose of preventing sticking of the humidifier bypass valve 69 as the control valve.

[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 (In) 74, and the channel 72A of a humidifier 70. Among the cathode supply channel 62, the upstream portion from the humidifier 70 is defined as the cathode supply channel 62A. Among the cathode supply channel 62, the downstream portion 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 (In) 74. The shutoff valve (In) 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 side of the air intake port (not shown) rather than the compressor 68. The pressure sensor 95 detects the pressure of the intake air (atmosphere) 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 cathode bypass channel 66 (which may also be called the cathode bypass flow rate) from the compressor supply flow rate. The humidifier 70 recovers the moisture contained in the cathode off-gas flowing through the channel 72B and adds the recovered moisture to the cathode gas flowing through the channel 72A. Humidifying the cathode gas flowing through the channel 72A is to prevent the over-drying of the electrode structure 24.

[0018] The humidifier bypass channel 63 communicates the cathode supply channel 62A with the cathode supply channel 62B. In the embodiment, the portion between the compressor 68 and the shutoff valve (In) 74 in the cathode supply channel 62A is communicated with the upstream portion from the air flow sensor 99 in the cathode supply channel 62B. The humidifier bypass channel 63 is provided with a humidifier bypass valve 69.

[0019] <Humidifier bypass valve> An example configuration of the humidifier bypass valve 69 will be explained with reference to Figures 5A and 5B. Figure 5A is a cross-sectional view illustrating a humidifier bypass valve 69 provided in the humidifier bypass passage 63. Figure 5B is a perspective view illustrating the main parts of the humidifier bypass valve 69. The humidifier bypass valve 69 is, for example, composed of a normally closed type butterfly valve.

[0020] In Figures 5A and 5B, the humidifier bypass valve 69 comprises a cylindrical housing V41, an annular valve seat portion V42 provided along the inner wall surface of the housing V41, a disc-shaped valve body V43, a shaft (not shown) that penetrates the valve body V43 and pivotally supports the valve body V43, and a spring V46 provided inside the housing V41 to hold the valve seat portion V42.

[0021] The housing V41 comprises a cylindrical housing body V411 and joints V412 provided on both ends of the housing body V411. A step V413 is formed on the inner wall surface of the housing body V411 along the circumferential direction, and the inner diameter on one end of the housing V411 (left side in Figure 5A) is larger than the inner diameter on the other end (right side in Figure 5A). The valve seat portion V42 is fitted to the inner wall surface on one end side of the step V413 of the housing V41. A recess V422 extending circumferentially is formed on the outer circumferential surface of the valve seat portion V42, and a rubber ring V421 that holds the valve seat portion V42 is provided in the recess V422. In other words, the rubber ring V421 is provided on the inner wall surface of the housing V41.

[0022] The valve body V43 comprises a disc-shaped main body V431 and a shaft penetration portion V432 provided at one end of the main body V431 (right side in Figure 5A) through which a shaft axis (not shown) passes, forming a through hole V433. The valve body V43 is positioned so that the side opposite to the shaft penetration portion V432 faces the cathode supply passage 62B. The peripheral edge of the valve body V431 on the cathode supply passage 62B side is the valve seal surface V44. One of the valve seat portion V42 and the valve body V43 is made of stainless steel or a non-ferrous metal, while the other is made of resin or rubber (elastic material). In this embodiment, the valve seat portion V42 is made of an elastic material, so that the valve seat portion V42 itself functions as a sealing member.

[0023] A shaft (not shown) passing through the through-hole V433 of the valve body V43 is rotatably supported by a bearing (not shown) provided on the housing V41 side. When this shaft is rotationally driven by a drive mechanism (not shown), the valve body V43 rotates together with the shaft. The spring V46 is located on one end of the housing V41 (the left side in Figure 5A) relative to the step V413. The spring V46 biases the valve seat portion V42 toward the step V413 via the annular support portion V47.

[0024] The humidifier bypass valve 69 described above operates as follows: As shown in Figures 5B (1) to (4), the valve body V43, which is a movable part, rotates so that the extension direction of the valve body V43 becomes approximately perpendicular to the extension direction of the housing V41. When the valve sealing surface V44 of the valve body V43 seats on the annular valve seat portion V42, which acts as the valve seat, the humidifier bypass valve 69 closes. Figure 5B (4) shows the closed state. In the closed position, the rubber ring V421 aligns the valve body V43. Additionally, the spring V46 biases the valve seat portion V42 toward the valve body V43.

[0025] Meanwhile, as the valve body V43 rotates and its extension direction approaches parallel to the extension direction of the housing V41, the peripheral edge of the valve body V43 separates from the valve seat portion V42, and the humidifier bypass valve 69 opens. Figures 5B (1) to (3) illustrate intermediate openings between fully open and fully closed, with the magnitude of the opening being (1) > (2) > (3).

[0026] Returning to Figure 1, the cathode discharge channel 64 connects the cathode outlet 19B and the inlet of the diluent 60. The cathode discharge channel 64 is provided with the channel 72B of the humidifier 70 and a sealing valve (Out) 76. The portion of the cathode discharge channel 64 upstream of the humidifier 70 is designated as the cathode discharge channel 64A. The portion of the cathode supply channel 62 downstream of the humidifier 70 is designated as the cathode discharge channel 64B. The sealing valve (Out) 76 is provided in the cathode discharge channel 64B.

[0027] The discharge pipe 100 is, for example, a hollow pipe approximately 1 m in length. The inlet 100A of the discharge pipe 100 is connected to the outlet of the diluent 60. The outlet 100C of the discharge pipe 100 is located, for example, under the floor in the approximate center of the vehicle. By providing the discharge pipe 100, the gas diluted in the diluent 60 (the combined gas formed by the convergence of the cathode-off gas that flowed through the cathode discharge channel 64B and the anode-off gas that flowed 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.

[0028] The cathode bypass channel 66 connects the cathode supply channel 62A and the cathode discharge channel 64B. For example, the cathode bypass channel 66 connects the portion of the cathode supply channel 62A between the compressor 68 and the sealing valve (In) 74 and the portion of the cathode discharge channel 64B downstream of the sealing valve (Out) 76. A cathode bypass valve 78 is provided in the cathode bypass channel 66.

[0029] The cooling system 20 has components for supplying refrigerant to the fuel cell stack 12 and components for discharging refrigerant from the fuel cell stack 12. The cooling system 20 has a refrigerant supply channel 84 and a refrigerant discharge channel 86. The cooling system 20 also has a refrigerant pump 88, a radiator 90, and a temperature sensor 92.

[0030] A refrigerant flow path (not shown) for cooling the fuel cell stack 12 is formed inside the fuel cell stack 12. A refrigerant supply flow path 84 connects the outlet of the radiator 90 to the inlet of the refrigerant flow path. A refrigerant pump 88 is provided in the refrigerant supply flow path 84. A refrigerant discharge flow path 86 connects the outlet of the refrigerant flow path to the inlet of the radiator 90. A temperature sensor 92 is provided in the refrigerant discharge flow path 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.

[0031] 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 system startup control unit 913, a standby power generation control unit 914, a normal power generation control unit 915, a power generation control unit 916 when stopped, and a stop control unit 917. 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.

[0032] 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. The memory unit 912 may also be used as a memory device for storing valve opening information, which will be described later. The valve opening information is information indicating that the humidifier bypass valve 69 has opened during a series of power generation control operations. In this embodiment, if the humidifier bypass valve 69 opens before the stop process, the valve opening information is recorded in the memory unit 912. The humidifier bypass valve 69 opens exclusively when warm-up power generation is performed.

[0033] The control unit 911 receives detection signals from various sensors provided in the fuel cell system 10. Based on instructions from a control unit (not shown) and the respective detection signals, the control unit 911 outputs control signals to control each of the valves, injectors 50, compressors 68, refrigerant pumps 88, etc. This controls the power generation of the fuel cell system 10. The control unit 911 may delegate control to a system startup control unit 913, a standby power generation control unit 914, a normal power generation control unit 915, a shutdown power generation control unit 916, and a shutdown control unit 917. In this case, each of the valves, injectors 50, compressors 68, refrigerant pumps 88, etc., operates according to the control signals from the control unit 911 or each control unit.

[0034] Figure 2 is a diagram illustrating an overview of the power generation control of the fuel cell system 10. The control unit 911 or each control unit performs a series of power generation controls along the time axis indicated by the arrows moving from left to right in Figure 2, including start-up control to start the fuel cell system 10 from a standby state, normal power generation control to cause the fuel cell system 10 to generate power, and stop-down control to stop the fuel cell system 10 and put it into a standby state. This series of power generation controls may also be called the driving cycle of the fuel cell system 10.

[0035] (Startup control) When the control unit 911 receives a power generation instruction (which may also be called a start instruction) from a control unit (not shown), the system start control unit 913 performs start control on the standby fuel cell system 10. Standby state refers to a state in which the fuel cell system 10 is capable of receiving instructions.

[0036] (Warm-up power generation control) When the stack temperature detected by the temperature sensor 92 during a power generation instruction is lower than a predetermined first temperature, the control unit 911 performs standby power generation control via the standby power generation control unit 914 to cause the fuel cell system 10 to perform warm-up power generation. The first temperature corresponds to the temperature at which the refrigerant may freeze. Warm-up power generation refers to power generation that increases the amount of heat generated in the fuel cell stack 12 compared to normal power generation by, for example, relatively reducing the supply flow rate of cathode gas to the anode gas to perform low-efficiency power generation. In this embodiment, standby power generation and warm-up power generation are synonymous. Warm-up power generation may also be simply called warm-up. Furthermore, the standby power generation control unit 914 determines that warm-up is complete when the stack temperature reaches a predetermined second temperature that is higher than the first temperature, or when a predetermined time has elapsed since the start of warm-up power generation. The second temperature corresponds to the temperature at which the stack has warmed up sufficiently. When the stack temperature reaches a predetermined second temperature higher than the first temperature, the humidifier bypass valve 69 is opened to supply cathode gas that has not been humidified by the humidifier 70 to the fuel cell stack 12, thereby drying the fuel cell stack 12.

[0037] (Normal power generation control) The control unit 911 performs normal power generation control, which causes the fuel cell system 10 to perform normal power generation, based on a power generation target from a control unit (not shown) and controlled by a normal power generation control unit 915. The normal power generation control unit 915 may prevent over-drying of the electrode structure 24 by adjusting the opening degree of the humidifier bypass valve 69, for example, based on the stack temperature detected by the temperature sensor 92 during power generation (humidification assistance).

[0038] (Stop control) When the control unit 911 receives a stop command from a control unit (not shown), the stop control unit 917 performs stop control on the fuel cell system 10. Figure 3 is a time chart illustrating the flow of the stop process. The stop process consists of stop process-1 and stop process-2. If a stop command is received at time t1 in Figure 3, the stop control unit 917 initiates stop process-1. When stop process-1 is initiated, the rotational speed of the compressor 68 is reduced compared to normal power generation, and the total amount of cathode gas discharged from the compressor 68 decreases.

[0039] (Power generation control during shutdown) Furthermore, the stop control unit 917 includes stop power generation control by the stop power generation control unit 916 in the stop process-1 as needed. Stop power generation refers to power generation to charge the battery 300 to a predetermined target SOC (State of Charge, which may also be called the battery charge rate) in preparation for the next start-up. In the example in Figure 3, stop power generation is performed from time t1 to time t2.

[0040] At time t2, the stop control unit 917 initiates nitrogen filling in stop process-1. The stop control unit 917, for example, narrows the opening of the sealing valve (Out) 76 to an intermediate opening, and then further narrows it to an opening of 0 (zero). The intermediate opening is the opening between fully open (opening 100) and fully closed (opening 0). As a result, even after power generation during shutdown, oxygen in the cathode gas of the outlet piping of the fuel cell stack 12 is consumed, and the relative amount of nitrogen increases.

[0041] The stop control unit 917 initiates stop process-2 at time t3. As stop process-2, the stop control unit 917 performs oxygen consumption near the electrode structure 24, air sealing, and pressure testing. For example, until time t4 when the sealing valve (In) 74 is fully closed, the remaining oxygen in the fuel cell stack 12 is further consumed (oxygen consumption). When the sealing valve (In) 74 is closed at time t4, the cathode gas supplied to the fuel cell stack 12 is cut off, resulting in an air-sealed state. The stop control unit 917 checks the pressure of the anode gas detected by the pressure sensor 93 (pressure check) and stops the operation of the compressor 68 at time t6. The results of the pressure check are used to determine the presence or absence of hydrogen and to determine whether the stop is complete. As a result, the series of power generation control processes end at time t7 (device shutdown), and the device transitions to a standby state. Thus, the control device 900 performs a series of power generation controls, including at least start control based on a start instruction, normal power generation control based on a power generation target (a target amount of power generation instructed by a control unit not shown), and stop control based on a stop instruction.

[0042] <Fluid flow> 1. Anode System The fluid flow in the anode system 16 shown 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.

[0043] 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.

[0044] 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.

[0045] 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 (In) 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.

[0046] With the sealing valve (Out) 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. As described above, the moisture in the cathode-off gas flowing through the cathode discharge channel 64 can also be used to humidify the cathode gas in the humidifier 70.

[0047] With the cathode bypass valve 78 open, the cathode gas flows through the cathode bypass passage 66 and the cathode discharge passage 64 and is discharged to the diluent 60. By using the cathode bypass passage 66, it is possible to change the amount of cathode gas supplied to the fuel cell stack 12 by adjusting the opening of the cathode bypass valve 78 without changing the rotational speed of the compressor 68 (in other words, changing the total amount of air discharged from the compressor 68).

[0048] With the humidifier bypass valve 69 open, the cathode gas is supplied to the fuel cell stack 12 by bypassing the humidifier 70 (in other words, via the humidifier bypass channel 63). Using the humidifier bypass channel 63 makes it possible to supply cathode gas that is not humidified by the humidifier 70 to the fuel cell stack 12. That is, the humidifier bypass valve 69 is opened when it is desired to supply dry air as cathode gas during warm-up power generation.

[0049] <Forced valve opening procedure> The humidifier bypass valve 69 may remain closed for extended periods depending on the operating environment of the fuel cell system 10. For example, if the fuel cell system 10 is used only in warm regions and there is no need to perform warm-up power generation, there is no opportunity to open the humidifier bypass valve 69 and supply dry air to the fuel cell stack 12. Therefore, the humidifier bypass valve 69 may remain closed for many years. Furthermore, if one of the valve seat portion V42 and valve body V43 is made of an elastic sealing member, the humidifier bypass valve 69 may become stuck in the closed position due to deterioration of the sealing member over time.

[0050] To prevent the aforementioned sticking, in this embodiment, if the humidifier bypass valve 69 is not opened during a series of power generation control operations, a forced opening process for the humidifier bypass valve 69 is included in the stop control. As an example, the stop control unit 917 outputs a forced open / close instruction signal to the humidifier bypass valve 69 at time t3 in Figure 3. Specifically, it outputs an open / close instruction signal to open the humidifier bypass valve 69, which is in the closed state (opening degree 0), to its full opening degree of 100, and then return it to the closed state. As a result, the opening degree of the humidifier bypass valve 69 changes as shown by the waveform at the bottom of Figure 3. The stop control unit 917 monitors the temporal change in the opening degree of the humidifier bypass valve 69 based on the opening / closing instruction signal, and performs a spring check and full-open learning. The spring check is a process to obtain information to determine whether the sealing performance of the humidifier bypass valve 69 can be guaranteed, and it refers to a process to confirm whether the time from power-off to reaching a predetermined opening is greater than or equal to a predetermined value. Furthermore, full-open learning is a process to correct for variations between the gear angle of the butterfly valve itself, as illustrated in Figures 5A and 5B, and the mounting position of the opening sensor (not shown). It refers to a process of learning (resetting) the position detected by the opening sensor when the opening of the humidifier bypass valve 69 is controlled to the fully closed (buttocked) position to be set to a controlled opening of 0 (zero).

[0051] <Explanation of the flowchart> Figures 4A and 4B are flowcharts illustrating an example of a series of power generation control processes executed by the control unit 911 based on a predetermined program. The control unit 911 performs the processes shown in Figures 4A and 4B when the fuel cell system 10 is ON (for example, when the vehicle's ignition switch (not shown) is ON).

[0052] In step S10 of Figure 4A, when the control unit 911 receives a power generation instruction from a control unit (not shown), the system startup control unit 913 performs startup control on the standby fuel cell system 10 and proceeds to step S20.

[0053] In step S20, the control unit 911 determines whether the stack temperature is below the first temperature. If the detection signal from the temperature sensor 92 indicates that the stack temperature is below the first temperature, the control unit 911 affirms step S20 and proceeds to step S30; otherwise, it negates step S20 and proceeds to step S40. The first temperature can also be determined by the control unit 911 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.

[0054] In step S30, the control unit 911, using the standby power generation control unit 914, performs standby power generation control to cause the fuel cell system 10 to perform warm-up power generation, and then proceeds to step S40. In step S40, the control unit 911, using the normal power generation control unit 915, performs normal power generation control to cause the fuel cell system 10 to perform normal power generation, and then proceeds to step S50.

[0055] In step S50, the control unit 911 determines whether or not there is a stop instruction. If the control unit 911 receives a stop instruction from a control unit (not shown) (corresponding to time t1 in Figure 3), it affirms step S50 and starts stop process-1. As a result, the stop control unit 917 starts stop process-1 on the fuel cell system 10 and proceeds to step S60. If the control unit 911 does not receive a stop instruction, it negates step S50 and returns to step S40, continuing normal power generation control by the normal power generation control unit 915.

[0056] In step S60, the control unit 911 determines whether or not power generation is necessary during shutdown. If the State of Charge (SOC) of the battery 300 is less than or equal to the target SOC, the control unit 911 affirms step S60 and proceeds to step S70. If the SOC is not less than or equal to the target SOC, the control unit 911 negates step S60 and proceeds to step S80.

[0057] In step S70, the control unit 911, using the power generation control unit 916 during shutdown, performs power generation control during shutdown to cause the fuel cell system 10 to generate power during shutdown, and then proceeds to step S80. In step S80, the control unit 911 causes the stop control unit 917 to perform stop control.

[0058] The details of the stop control in step S80 will be explained with reference to the flowchart in Figure 4B. In step S810 in Figure 4B, the stop control unit 917 performs nitrogen filling and proceeds to step S820 (corresponding to time t2 in Figure 3).

[0059] In step S820, the stop control unit 917 determines whether or not there is valve opening information. If the storage unit 912 does not store valve opening information, the stop control unit 917 affirms step S820 and proceeds to step S830. If the storage unit 912 does store valve opening information, the stop control unit 917 denies step S820 and proceeds to step S850.

[0060] In step S830, the stop control unit 917 outputs a forced opening / closing instruction signal to the humidifier bypass valve 69 at time t3 in Figure 3 (forced opening), and proceeds to step S840 (corresponding to time t3 in Figure 3).

[0061] In step S840, the stop control unit 917 performs an ancillary process of spring check and full-open learning before proceeding to step S850. In step S850, the stop control unit 917 performs oxygen consumption as stop process-2 and proceeds to step S860 (corresponding to times t3 to t5 in Figure 3). In step S860, the stop control unit 917 performs a pressure test as stop process-2 and proceeds to step S870 (corresponding to times t5 to t6 in Figure 3).

[0062] In step S870, the stop control unit 917 confirms that the device has stopped and terminates the process shown in Figure 4B, and also terminates the process shown in Figure 4A (corresponding to time t7 in Figure 3).

[0063] According to the embodiment described above, the following effects and advantages are achieved. (1) A fuel cell system 10 including a fuel cell stack 12 that generates electricity using anode gas and cathode gas includes a control device 900 that performs a series of power generation controls including at least a start control (S10) based on a start instruction, a normal power generation control (S40) based on a power generation target, and a stop control (S80) based on a stop instruction; a humidifier bypass valve 69 as a normally closed control valve in which a movable valve body V43 abuts against a sealing member of a valve seat portion V42 as a valve seat in a closed state; and a storage unit 912 as a storage device that stores opening information indicating that the humidifier bypass valve 69, which opens under predetermined conditions, has opened. The control device 900 includes a forced opening process (S830) in the stop control (S80) that opens the humidifier bypass valve 69 if the humidifier bypass valve 69 has not opened before the stop control (S80) in the series of power generation controls. With this configuration, if the humidifier bypass valve 69 is not open during the series of power generation control (in other words, if the opening information is not stored in the memory unit 912), the humidifier bypass valve 69 is opened by the forced opening process (S830) included in the stop control (S80). This prevents the humidifier bypass valve 69 from remaining closed for a long period of time, causing the sealing member to weld together due to aging deterioration and preventing the humidifier bypass valve 69 from becoming stuck in the closed position.

[0064] (2) In the fuel cell system 10 described in (1) above, the humidifier bypass valve 69 is provided in the cathode supply channel 62 that supplies cathode gas to the fuel cell stack 12, and the control device 900 includes in the stop control (S80) a forced valve opening process (S830) to be performed before or during the oxygen consumption process (S850) that consumes the oxygen remaining in the fuel cell stack 12. With this configuration, even if oxygen flows into the fuel cell stack 12 by opening the humidifier bypass valve 69 through the forced valve opening process (S830), the oxygen in the cathode channel 38 can be depleted by the oxygen consumption process (S850), thus preventing deterioration due to residual oxygen in the cathode channel 38.

[0065] (3) In the fuel cell system 10 described in (1) or (2) above, the control device 900 performs at least one of the humidifier bypass valve 69 spring check process and opening degree learning process as an ancillary process in conjunction with the forced valve opening process (S830) (S840). With this configuration, by performing a spring check and opening degree learning process for the humidifier bypass valve 69 in conjunction with the forced valve opening process (S830), it becomes possible to ensure the sealing performance of the cathode supply channel 62.

[0066] (4) The fuel cell system 10 described in (3) above further comprises a humidifier 70 for humidifying the cathode gas and a humidifier bypass channel 63 for bypassing the humidifier 70, and the humidifier bypass valve 69 is provided in the humidifier bypass channel 63. With this configuration, even though the humidifier bypass valve 69 is only opened in limited situations such as when bypassing the humidifier 70, it is possible to prevent the humidifier bypass valve 69 from becoming stuck in the closed position by performing a forced opening procedure (S830).

[0067] (5) In the fuel cell system 10 described in (4) above, the predetermined condition for the humidifier bypass channel 63 to open during a series of power generation control is that the fuel cell system 10 is warmed up. With this configuration, even if the humidifier bypass valve 69 is opened only during warm-up power generation at low temperatures, for example, if the opening information is not stored in the memory unit 912 (i.e., warm-up is not performed), a forced opening process (S830) can be performed to prevent the humidifier bypass valve 69 from becoming stuck in the closed state.

[0068] The above embodiment can be modified into various forms. Modifications will be described below. (Variation 1) In the embodiment described above, an example was explained in which the forced opening process (S830) of the humidifier bypass valve 69 is performed at the start of oxygen consumption in stop process-2 (time t3 in Figure 3). Alternatively, the procedure may be performed before the start of oxygen consumption in stop process-2, or during the oxygen consumption process after the start of oxygen consumption.

[0069] (Modification 2) In the embodiment described above, an example was explained in which both a spring check and full-open learning are performed as an ancillary process (S840) attached to the forced valve opening process (S830) for the humidifier bypass valve 69. Alternatively, the configuration may be such that only one of the spring check and full-open learning is performed as the ancillary process (S840).

[0070] (Variation 3) In the embodiment described above, an example was explained in which the humidifier bypass valve 69 is configured with a butterfly valve. However, the humidifier bypass valve 69 is not limited to a butterfly valve and may be configured with other types of valves.

[0071] 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]

[0072] 10 Fuel cell system, 12 Fuel cell stack, 36 Anode channel, 38 Cathode channel, 40 Anode supply channel, 42 Anode discharge channel, 62 Cathode supply channel, 63 Humidifier bypass channel, 64, 64A, 64B Cathode discharge channel, 66 Cathode bypass channel, 68 Compressor, 69 Humidifier bypass valve, 74 Sealing valve (In), 76 Sealing valve (Out), 78 Cathode bypass valve, 900 Control device, 911 Control unit, 912 Memory unit, 913 System startup control unit, 914 Standby power generation control unit, 915 Normal power generation control unit, 916 Power generation control unit during shutdown, 917 Shutdown control unit, 300 Battery

Claims

1. A fuel cell system including a fuel cell stack that generates electricity using anode gas and cathode gas, A control device that performs a series of power generation controls, including at least start control based on a start instruction, normal power generation control based on a power generation target, and stop control based on a stop instruction, A normally closed type control valve in which a movable valve body contacts the sealing member of the valve seat in the closed state, The system includes a memory device that stores opening information indicating that the control valve, which opens under predetermined conditions, has opened, The control device includes in the stop control a forced valve opening process to open the control valve if the control valve has not been opened before the stop control in the series of power generation control operations. A fuel cell system characterized by the following features.

2. In the fuel cell system according to claim 1, The control valve is provided in the cathode supply path that supplies the cathode gas to the fuel cell stack. The control device includes in the stop control the forced valve opening process to be performed before or during the oxygen consumption process that consumes the oxygen remaining in the fuel cell stack. A fuel cell system characterized by the following features.

3. In the fuel cell system according to claim 1 or 2, The control device performs at least one of the following in conjunction with the forced valve opening process: a spring check process and an opening degree learning process for the control valve. A fuel cell system characterized by the following features.

4. In the fuel cell system according to claim 3, A humidifier for humidifying the cathode gas, The system further comprises a bypass channel that bypasses the humidifier, The control valve is provided in the bypass passage, A fuel cell system characterized by the following features.

5. In the fuel cell system according to claim 4, The predetermined condition under which the control valve opens during the series of power generation control operations is that the fuel cell system is warmed up. A fuel cell system characterized by the following features.

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