Fuel cell system and its control method

Abstract

To suppress fuel cell degradation caused by an increase in cathode potential during soaking, even when the remaining amount of anode gas is low. [Solution] The fuel cell system includes an ECU that operates a cathode gas supply device and an anode gas supply device. The ECU is configured to perform a power generation shutdown process in which, after closing the cathode sealing valve of the cathode gas supply device when power generation is stopped, the supply of anode gas to the fuel cell stack is stopped when the anode pressure is higher than the cathode pressure, and the purge valve of the anode gas supply device is closed. After the completion of this power generation shutdown process, if predetermined start conditions are met, a fuel supply process is performed in which anode gas is supplied to the fuel cell stack until the anode pressure reaches a predetermined completion determination pressure. After the start of the fuel supply process, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the ECU terminates the fuel supply process even if the anode pressure is below the completion determination pressure.

Description

Technical Field

[0001] The present invention relates to a fuel cell system and a control method therefor. Background Art

[0002] In recent years, research and development on fuel cells that contribute to energy efficiency have been carried out to enable more people to secure access to affordable, reliable, sustainable and advanced energy.

[0003] In recent fuel cell systems, in order to suppress deterioration of the fuel cell (specifically, the electrolyte membrane, the anode electrode, the cathode electrode, etc.) caused by an increase in cathode potential during soaking of the fuel cell, anode gas (hydrogen gas) is supplied to the fuel cell during soaking. In many cases, the hydrogen partial pressure of the anode electrode during soaking is maintained at a predetermined pressure or higher by periodically performing a fuel supply process for supplying the fuel (see, for example, Patent Document 1). Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2009-117056 Summary of the Invention Problem to be Solved by the Invention

[0005] By the way, in the invention described in Patent Document 1, sufficient study has not been conducted on the remaining amount of anode gas supplied to the fuel cell during soaking. That is, in many fuel cell systems, the anode gas stored in a high-pressure tank is supplied to the fuel cell, but in the invention described in Patent Document 1, when the remaining amount of anode gas in the high-pressure tank is low, how much amount of anode gas should be supplied has not been sufficiently studied.

[0006] The present invention aims to achieve a fuel cell system that can suppress fuel cell degradation caused by an increase in cathode potential during soaking, even when the remaining amount of anode gas is low, and thereby contribute to energy efficiency. [Means for solving the problem]

[0007] (1) The fuel cell system according to the present invention (for example, fuel cell system 1 described later) comprises a fuel cell (for example, fuel cell stack 2 described later) that generates electricity when anode gas and cathode gas are supplied, a cathode gas supply device (for example, cathode gas supply device 4 described later) that supplies cathode gas to the cathode channel (for example, cathode channel 22 described later) of the fuel cell, an anode gas supply device (for example, anode gas supply device 3 described later) that supplies anode gas to the anode channel (for example, anode channel 21 described later) of the fuel cell, and control means (for example, ECU 6 described later) that operates the cathode gas supply device and the anode gas supply device, wherein the cathode gas supply device comprises cathode sealing valves (for example, inlet sealing valve 421 and outlet sealing valve 431 described later) provided on the inlet and outlet sides of the cathode channel, and the anode gas supply The device includes an anode discharge valve (for example, a purge valve 332 described later) provided on the outlet side of the anode flow path, and the control means is configured to perform a stop process (for example, a power generation stop process described later) in which, after closing the cathode sealing valve when power generation of the fuel cell is stopped, the supply of anode gas to the fuel cell is stopped when the anode pressure of the fuel cell is higher than the cathode pressure and the anode discharge valve is closed, and a fuel supply process (for example, a fuel supply process described later) in which, after the end of the stop process, a predetermined start condition is met and a fuel supply process is performed in which anode gas is supplied to the fuel cell until the anode pressure reaches a predetermined completion determination pressure, and the control means is configured to perform a stop start of the fuel supply process, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the fuel supply process is terminated even if the anode pressure is less than the completion determination pressure.

[0008] (2) In this case, the anode gas supply device comprises an anode gas supply source (for example, a hydrogen tank 31 described later), an anode gas supply passage (for example, a hydrogen supply pipe 32 described later) connecting the anode gas supply source and the inlet side of the anode flow path, an injector (for example, an injector 322 described later) provided in the anode gas supply passage, and an anode gas return passage (for example, a hydrogen return pipe 34 described later) connecting the outlet side of the anode flow path and the anode gas supply passage downstream of the injector, and the control means preferably acquires the pressure detected by a first pressure detection device (for example, an anode pressure sensor 28 described later) provided between the injector and the fuel cell in the anode gas supply passage as the anode pressure.

[0009] (3) In this case, if the control means terminates the fuel supply process before the anode pressure reaches the completion determination pressure, it is preferable that the control means prohibits the next fuel supply process and notifies the user that the anode gas supply source is in a state of insufficient remaining anode gas.

[0010] (4) In this case, it is preferable that the control means start the fuel supply process with the start condition being that a predetermined time has elapsed since the end of the stop process.

[0011] (5) In this case, it is preferable that the control means starts the fuel supply process with the start condition being that the anode pressure drops to a predetermined pressure from the end of the stop process.

[0012] (6) In this case, the anode gas supply device further comprises a pressure reducing valve (for example, a pressure reducing valve 324 described later) provided between the injector and the anode gas supply source in the anode gas supply path, and the control means preferably prohibits the next fuel supply process if, at the end of the fuel supply process, the pressure detected by a second pressure detection device provided between the anode gas supply source and the pressure reducing valve is less than a predetermined prohibition determination pressure.

[0013] (7) A control method for a fuel cell system according to the present invention comprises: a first step of closing the cathode sealing valve when power generation of the fuel cell is stopped, stopping the supply of anode gas to the fuel cell and closing the anode discharge valve when the anode pressure of the fuel cell is higher than the cathode pressure; and a second step of supplying anode gas to the fuel cell until the anode pressure reaches a predetermined completion determination pressure, provided that predetermined start conditions are met after the completion of the first step, and that after the start of the second step, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the second step is terminated even if the anode pressure is less than the completion determination pressure. [Effects of the Invention]

[0014] (1) When the fuel cell stops generating power, the control means closes the cathode sealing valve and then performs a stop process that stops the supply of anode gas to the fuel cell and closes the anode discharge valve when the anode pressure of the fuel cell is higher than the cathode pressure. After the completion of such a stop process, if predetermined start conditions are met, the control means performs a fuel supply process that supplies anode gas to the fuel cell until the anode pressure reaches a predetermined completion determination pressure. This makes it possible to maintain the hydrogen partial pressure at the anode electrode of the fuel cell during soaking at or above a predetermined pressure, thereby suppressing the deterioration of the fuel cell caused by the rise in cathode potential during soaking. Furthermore, after the start of such a fuel supply process, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the control means terminates the ongoing fuel supply process even if the anode pressure is below the completion determination pressure.Therefore, according to the present invention, even if the remaining amount of anode gas is insufficient at the start of the fuel supply process described above, the remaining anode gas can be supplied to the fuel cell as much as possible, thereby suppressing the deterioration of the fuel cell caused by the rise in cathode potential during soaking as much as possible, and ultimately contributing to energy efficiency.

[0015] (2) The control means acquires the pressure detected by a first pressure detection device located on the fuel cell side of the injector in the anode gas supply path connecting the anode gas supply source and the inlet side of the anode flow path as the anode pressure. In this way, the present invention determines the timing to terminate the fuel supply process based on the pressure fluctuation range on the lower pressure side of the injector in the anode gas supply path from the high-pressure side anode gas supply source to the low-pressure side fuel cell. As a result, even if the remaining amount of anode gas in the anode gas supply source is insufficient, the remaining anode gas can be supplied to the fuel cell as much as possible, thereby suppressing the deterioration of the fuel cell as much as possible.

[0016] (3) If the control means terminates the fuel supply process before the anode pressure reaches the completion determination pressure, in other words, if the fuel supply process is terminated because there is insufficient remaining anode gas in the anode gas supply source, it will prohibit the next fuel supply process and notify the user that there is insufficient remaining anode gas in the anode gas supply source. This will minimize the consumption of anode gas in the fuel cell during soaking in preparation for the next start-up of the fuel cell system, and will also make the user aware that there is insufficient remaining anode gas.

[0017] (4) The control means starts the fuel supply process when a predetermined time has elapsed from the end of the shutdown process. In other words, the control means starts the fuel supply process when a predetermined time has elapsed from the end of the shutdown process, regardless of the remaining amount of anode gas at that time. Therefore, according to the present invention, even if the remaining amount of anode gas is insufficient, as much anode gas as possible can be supplied to the fuel cell, so that deterioration of the fuel cell caused by the rise in cathode potential during soaking can be suppressed as much as possible.

[0018] (5) The control means starts the fuel supply process on the condition that the anode pressure drops by a predetermined pressure from the end point of the stop process. In other words, when the anode pressure drops by the predetermined pressure from the end point of the stop process, the control means starts the fuel supply process regardless of the remaining amount of anode gas at that time. Therefore, according to the present invention, even when the remaining amount of anode gas is insufficient, anode gas can be supplied to the fuel cell as much as possible, so deterioration of the fuel cell caused by the increase in cathode potential during soaking can be suppressed as much as possible.

[0019] (6) When the fuel supply process ends, if the pressure detected by a second pressure detection device provided between the anode gas supply source and the pressure reducing valve in the anode gas supply path is less than a predetermined prohibition determination pressure, the control means prohibits execution of the next fuel supply process. This can prevent an excessive drop in pressure in the anode gas supply source during soaking, thereby protecting the anode gas supply source.

[0020] (7) According to the control method for a fuel cell system of the present invention, even when the remaining amount of anode gas during soaking is insufficient, the remaining anode gas can be supplied to the fuel cell, so deterioration of the fuel cell caused by the increase in cathode potential during soaking can be suppressed as much as possible, which in turn can contribute to improved energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [Figure 1] It is a diagram showing the configuration of the fuel cell system according to the first embodiment of the present invention. [Figure 2] It is a flowchart showing the specific procedure of power generation stop processing. [Figure 3A] It is a flowchart showing the specific procedure of anode gas filling processing (part 1). [Figure 3B] It is a flowchart showing the specific procedure of anode gas filling processing (part 2). [Figure 4A] It is a time chart showing a first example of changes in anode pressure realized by power generation stop processing and anode gas sealing processing. [Figure 4B] It is a time chart showing a second example of changes in anode pressure achieved by power generation stop processing and anode gas sealing processing. [Figure 5] It is a part of a flowchart showing a specific procedure of anode gas filling processing in the fuel cell system according to the second embodiment of the present invention. [Figure 6] It is a part of a flowchart showing a specific procedure of anode gas filling processing in the fuel cell system according to the third embodiment of the present invention. [Figure 7] It is a part of a flowchart showing a specific procedure of anode gas filling processing in the fuel cell system according to the fourth embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

[0022] <First Embodiment> Hereinafter, a fuel cell system according to the first embodiment of the present invention will be described with reference to the drawings.

[0023] FIG. 1 is a diagram showing a configuration of a fuel cell system 1 according to the present embodiment. The fuel cell system 1 comprises: a fuel cell stack 2 that generates power when supplied with anode gas and cathode gas; an anode gas supply device 3 that supplies hydrogen as anode gas to an anode flow path 21 of the fuel cell stack 2; a cathode gas supply device 4 that supplies air as cathode gas to a cathode flow path 22 of the fuel cell stack 2; a cooling system 5 that cools the fuel cell stack 2; a battery B that can store electric power generated by the fuel cell stack 2; a travel motor M that rotates tires (not shown) by electric power supplied from the fuel cell stack 2 and the battery B; a power circuit 7 that electrically connects the battery B, the travel motor M and the fuel cell stack 2; and an ECU 6 which is a computer that controls these components. Hereinafter, a case where the fuel cell system 1 is mounted on a fuel cell vehicle that travels using the tires as drive wheels will be described.

[0024] The fuel cell stack 2 is, for example, a stack structure in which tens to hundreds of fuel cell cells are stacked. Each fuel cell is constructed by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure consists of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Typically, both electrodes are formed from a catalyst layer that performs oxidation-reduction reactions in contact with the solid polymer electrolyte membrane, and a gas diffusion layer in contact with this catalyst layer. In this fuel cell stack 2, when hydrogen is supplied to the anode channel 21 formed on the anode electrode side and oxygen-containing air is supplied to the cathode channel 22 formed on the cathode electrode side, electricity is generated by these electrochemical reactions. The electricity generated by the fuel cell stack 2 is supplied to loads such as the driving motor M and battery B via the power circuit 7.

[0025] The anode gas supply device 3 includes a hydrogen tank 31 for storing hydrogen gas at high pressure, a hydrogen supply pipe 32 from the hydrogen tank 31 to the inlet side of the anode flow path 21 of the fuel cell stack 2, a hydrogen discharge pipe 33 from the outlet side of the anode flow path 21 to a diluent (not shown) provided in the cathode gas supply device 4, and a hydrogen reflux pipe 34 that branches off from the hydrogen discharge pipe 33 and goes to the hydrogen supply pipe 32.

[0026] The hydrogen supply pipe 32 is a pipe that connects the hydrogen tank 31 to the inlet side of the anode flow path 21, and guides the high-pressure hydrogen gas stored in the hydrogen tank 31 to the anode flow path 21 as anode gas. The hydrogen supply pipe 32 is equipped with a pressure reducing valve 324, a shut-off valve 321, an injector 322, and an ejector 323 in order from the high-pressure side (hydrogen tank 31) to the low-pressure side (fuel cell stack 2).

[0027] The hydrogen tank 31 is equipped with a tank valve 311 that opens and closes in response to a command signal from the ECU 6. The hydrogen tank 31 is connected to the hydrogen supply pipe 32 via this tank valve 311. The pressure reducing valve 324 reduces the hydrogen gas supplied from the hydrogen tank 31 to a predetermined pressure. The shut-off valve 321 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. The injector 322 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. When the injector 322 is opened, high-pressure hydrogen gas supplied via the shut-off valve 321 is injected towards the ejector 323. The amount of hydrogen gas injected from the injector 322 is controlled by PWM control by the ECU 6. The ejector 323 mixes the hydrogen gas injected from the injector 322 with the anode-off gas discharged from the hydrogen reflux pipe 34 (i.e., hydrogen-containing gas discharged from the outlet side of the anode flow path 21) and injects it towards the inlet side of the anode flow path 21. Therefore, in such an anode gas supply device 3, hydrogen gas stored in the hydrogen tank 31 can be supplied to the fuel cell stack 2 by opening and closing the injector 322 while both the tank valve 311 and the shut-off valve 321 are open.

[0028] The hydrogen reflux pipe 34 is a pipe that connects the hydrogen discharge pipe 33, which is connected to the outlet side of the anode flow path 21, and the ejector 323, which is located downstream of the injector 322 in the hydrogen supply pipe 32, and guides a portion of the anode off gas flowing through the hydrogen discharge pipe 33 to the ejector 323. As a result, the hydrogen-containing anode off gas circulates together with the anode gas newly injected from the injector 322 within the circulation channel composed of the hydrogen supply pipe 32, anode flow path 21, hydrogen discharge pipe 33, hydrogen reflux pipe 34, and ejector 323.

[0029] The hydrogen discharge pipe 33 is a pipe connecting the outlet side of the anode flow path 21 to the diluent (not shown) of the cathode gas supply device 4. The hydrogen discharge pipe 33 is equipped with a catch tank 331 for storing water contained in the anode off-gas and a purge valve 332 for discharging the anode off-gas to the cathode gas supply device 4, in that order from the fuel cell stack 2 side toward the cathode gas supply device 4 side. The catch tank 331 is also equipped with a drain pipe 35 for discharging the accumulated water. This drain pipe 35 runs from the catch tank 331 to the downstream side of the hydrogen discharge pipe 333 beyond the purge valve 332. The drain pipe 35 is equipped with a drain valve 351. When this drain valve 351 is opened, the water accumulated in the catch tank 331 is discharged through the hydrogen discharge pipe 33 to the diluent (not shown). The purge valve 332 and the drain valve 351 are solenoid valves that open and close in response to command signals from the ECU 6.

[0030] The cathode gas supply device 4 includes an air compressor 41, an air supply pipe 42 leading from the air compressor 41 to the inlet of the cathode flow path 22, an air discharge pipe 43 leading from the discharge of the cathode flow path 22 to a diluent (not shown), an air bypass pipe 45 branching from the air discharge pipe 43 to the air supply pipe 42, and a humidifier 46 connecting the air discharge pipe 43 and the air supply pipe 42.

[0031] The air compressor 41 supplies outside air to the cathode channel 22 of the fuel cell stack 2 via the air supply pipe 42. The air compressor 41 operates in response to command signals from the ECU 6. The humidifier 46 recovers water contained in the gas discharged from the cathode channel 22 (hereinafter also referred to as "cathode-off gas") and uses the recovered water to humidify the air supplied by the air compressor 41. Due to the function of this humidifier 46, the MEA of the fuel cell stack 2 during power generation is maintained in a state suitable for power generation.

[0032] The air supply pipe 42 is provided with a humidifier bypass pipe 47 that bypasses the humidifier 46. This humidifier bypass pipe 47 is provided with a bypass valve 471. When the bypass valve 471 is opened, most of the air supplied from the air compressor 41 bypasses the humidifier 46 and is supplied to the fuel cell stack 2. The bypass valve 471 is a solenoid valve that opens and closes in response to a command signal from the ECU 6.

[0033] Furthermore, the air supply pipe 42 and the air discharge pipe 43 are equipped with an inlet sealing valve 421 and an outlet sealing valve 431, respectively. When these sealing valves 421 and 431 are closed, the inside of the cathode flow path 22 is isolated from the outside air. These sealing valves 421 and 431 are solenoid valves that open and close in response to command signals from the ECU 6.

[0034] The air bypass pipe 45 is a pipe that connects the high-pressure side air supply pipe 42 and the low-pressure side air discharge pipe 43. More specifically, the air bypass pipe 45 connects the air supply pipe 42 upstream of the humidifier 46 and the inlet sealing valve 421, and the air discharge pipe 43 downstream of the humidifier 46 and the outlet sealing valve 431. Therefore, a portion of the air supplied from the air compressor 41 bypasses the humidifier 46 and the cathode flow path 22, and is discharged to the air discharge pipe 43 via the air bypass pipe 45.

[0035] The air bypass pipe 45 is equipped with a back pressure control valve 451 for adjusting the back pressure in the cathode flow path 22 of the fuel cell stack 2. The back pressure control valve 451 is a solenoid valve that opens and closes in response to a command signal from the ECU 6.

[0036] The cooling system 5 includes a refrigerant circulation path 51 that includes the inside of the fuel cell stack 2 as part of its flow path, a cooling pump 52 that circulates refrigerant within the refrigerant circulation path 51, a radiator 53 provided upstream of the cooling pump 52 in the refrigerant circulation path 51, a thermovalve 54 provided downstream of the cooling pump 52 in the refrigerant circulation path 51, and a bypass pipe 55 that connects the thermovalve 54 to the upstream side of the radiator 53 in the refrigerant circulation path 51.

[0037] The fuel cell stack 2 is cooled by heat exchange with the refrigerant flowing through its internal passages. The radiator 53 cools the refrigerant by heat exchange with the outside air. The cooling pump 52 operates in response to command signals from the ECU 6. The rotational speed of the cooling pump 52 is controlled by the ECU 6. Increasing the rotational speed of the cooling pump 52 increases the flow rate of the refrigerant circulating in the refrigerant circulation path 51, which includes the fuel cell stack 2 and the radiator 53 in its refrigerant passages, thereby increasing the cooling capacity of the fuel cell stack 2.

[0038] The thermovalve 54 is a three-way valve that opens and closes in response to a command signal from the ECU 6. The opening ratio of the thermovalve 54 (the ratio of the opening on the refrigerant circulation path 51 side (100% to 0%) to the opening on the bypass pipe 55 side (0% to 100%)) is controlled by the ECU 6. When the opening ratio of the thermovalve 54 is set to the maximum (i.e., "1"), all the refrigerant discharged from the cooling pump 52 is supplied to the fuel cell stack 2, thereby increasing the cooling capacity of the fuel cell stack 2. When the opening ratio of the thermovalve 54 is set to the minimum (i.e., "0"), all the refrigerant discharged from the cooling pump 52 is supplied to the bypass pipe 55.

[0039] Battery B is a secondary battery capable of both discharging, which converts chemical energy into electrical energy, and charging, which converts electrical energy into chemical energy. In the following description, a so-called lithium-ion battery, which charges and discharges by the movement of lithium ions between electrodes, is used as Battery B, but the present invention is not limited to this. Battery B may also be a capacitor, for example.

[0040] The power circuit 7 consists of power lines connecting the fuel cell stack 2 to the drive motor M and battery B, a DC-DC converter installed in these power lines to step up or step down the DC power output from the fuel cell stack 2, and an inverter installed in these power lines to convert the DC power output from the DC-DC converter into three-phase AC power for supply to the drive motor M, and to convert the three-phase AC power supplied from the drive motor M into DC power for supply to the battery B. Multiple switching elements constituting these DC-DC converters and inverters are driven on / off according to gate drive signals generated at predetermined timings from a gate drive circuit (not shown) of the ECU 6. Therefore, the ECU 6 can control the flow of power between the fuel cell stack 2, battery B, and drive motor M in the power circuit 7 by operating the DC-DC converters and inverters using the gate drive circuit.

[0041] The ECU6 is a computer equipped with multiple functions, including a requested output acquisition function, a power generation control function, a temperature control function, an output control function, and a stack protection control function. The requested output acquisition function refers to the function in which the ECU6 acquires a requested output corresponding to the request for the output of the fuel cell stack 2 based on the amount of operation of the accelerator pedal, brake pedal, etc. (not shown) by the driver.

[0042] The power generation control function refers to the function in which the ECU 6 controls the power generation state of the fuel cell stack 2 by operating the anode gas supply device 3, cathode gas supply device 4, etc., based on the requested output. The temperature control function refers to the function in which the ECU 6 controls the temperature of the fuel cell stack 2 by operating the cooling system 5. The output control function refers to the function in which the ECU 6 controls the output of the fuel cell stack 2 so that the requested output is met by operating the DC-DC converter, inverter, etc., of the power circuit 7 based on the requested output.

[0043] The stack protection control function refers to a function in which the ECU6 periodically activates during the soaking of the fuel cell stack 2 by utilizing its built-in RTC (Real Time Clock) and performs processes to protect the fuel cell stack 2 during soaking, such as drying, power generation shutdown, anode gas filling, and fuel supply, as described below, as needed.

[0044] The ECU6 is connected to several sensors for monitoring the state of the fuel cell stack 2 during power generation, including a cell voltage sensor 24, a current sensor 26, a cathode pressure sensor 27, an anode pressure sensor 28, an intermediate pressure sensor 25, and an upstream pressure sensor 29.

[0045] The cell voltage sensor 24 detects the voltage of each fuel cell constituting the fuel cell stack 2 (so-called cell voltage) and transmits a signal approximately proportional to the detected value to the ECU 6. The current sensor 26 detects the output current of the fuel cell stack 2, more specifically the current output from the fuel cell stack 2 to loads such as the drive motor M and battery B via the power circuit 7, and transmits a signal approximately proportional to the detected value to the ECU 6.

[0046] The cathode pressure sensor 27 is installed, for example, between the inlet sealing valve 421 and the fuel cell stack 2 in the air supply pipe 42. The cathode pressure sensor 27 detects the pressure of the cathode gas between the inlet sealing valve 421 and the fuel cell stack 2 in the air supply pipe 42 and transmits a signal approximately proportional to the detected value to the ECU 6. The ECU 6 acquires the pressure detected by the cathode pressure sensor 27 installed in this position as the cathode pressure.

[0047] The hydrogen supply pipe 32 is equipped with an upstream pressure sensor 29, an intermediate pressure sensor 25, and an anode pressure sensor 28, in that order from the high-pressure hydrogen tank 31 to the low-pressure fuel cell stack 2.

[0048] The upstream pressure sensor 29 is installed, for example, between the hydrogen tank 31 and the pressure reducing valve 324 in the hydrogen supply pipe 32. The upstream pressure sensor 29 detects the pressure of the anode gas between the hydrogen tank 31 and the pressure reducing valve 324 in the hydrogen supply pipe 32 and transmits a signal approximately proportional to the detected value to the ECU 6. The ECU 6 acquires the pressure detected by the upstream pressure sensor 29 installed in such a location as the upstream pressure.

[0049] The intermediate pressure sensor 25 is installed, for example, between the shut-off valve 321 and the injector 322 in the hydrogen supply pipe 32. The intermediate pressure sensor 29 detects the pressure of the anode gas between the shut-off valve 321 and the injector 322 in the hydrogen supply pipe 32 and transmits a signal approximately proportional to the detected value to the ECU 6. The ECU 6 acquires the pressure detected by the intermediate pressure sensor 29 installed in such a location as the intermediate pressure.

[0050] The anode pressure sensor 28 is installed, for example, between the injector 322 and the fuel cell stack 2 in the hydrogen supply pipe 32. The anode pressure sensor 28 detects the pressure of the anode gas between the injector 322 and the fuel cell stack 2 in the hydrogen supply pipe 32 and transmits a signal approximately proportional to the detected value to the ECU 6. The ECU 6 acquires the pressure detected by the anode pressure sensor 28 installed in such a location as the anode pressure.

[0051] Figure 2 is a flowchart showing the specific procedure for stopping power generation. This power generation stopping process is performed by the ECU 6 when the fuel cell stack 2 stops generating power in order to suppress the deterioration of the fuel cell stack 2 during soaking and restarting. Here, "when the fuel cell stack 2 stops generating power" refers to the moment immediately after power generation by the fuel cell stack 2 has finished. More specifically, the ECU 6 performs the power generation stopping process shown in Figure 2, for example, immediately after the fuel cell stack 2 has finished generating power to drive the vehicle, or immediately after the fuel cell stack 2 has finished generating power during the drying process which is performed as appropriate during the soaking of the fuel cell stack 2. Here, the drying process refers to the process of raising the temperature and drying the inside of the fuel cell stack 2, and is performed as appropriate by the ECU 6 during the soaking of the fuel cell stack 2.

[0052] In response to the completion of power generation by the fuel cell stack 2, in step ST1, the ECU 6 first stops the supply of cathode gas and seals the cathode passage 22 of the fuel cell stack 2, and then proceeds to step ST2. More specifically, the ECU 6 stops the supply of cathode gas by stopping the air compressor 41 and closes the inlet sealing valve 421 and the outlet sealing valve 431. As a result, the inlet and outlet sides of the cathode passage 22 of the fuel cell stack 2 are sealed and isolated from the outside air.

[0053] Next, in step ST2, the ECU 6 seals the anode passage 21 of the fuel cell stack 2 while the anode pressure is higher than the cathode pressure, and then proceeds to step ST3. More specifically, the ECU 6 supplies anode gas to the anode passage 21 of the fuel cell stack 2 by driving the injector 322 while keeping the shut-off valve 321 and the tank valve 311 open until the anode pressure reaches a predetermined target pressure set to be higher than the cathode pressure. Then, in response to the anode pressure reaching the target pressure, the ECU 6 closes the shut-off valve 321 and the tank valve 311, and stops driving the injector 322 to stop the supply of anode gas to the fuel cell stack 2, and also closes the purge valve 332. As a result, the inlet and outlet sides of the anode passage 21 of the fuel cell stack 2 are sealed while the anode pressure is higher than the cathode pressure.

[0054] Next, in step ST3, the ECU6 stores the current time as the end time of the power generation shutdown process, and then proceeds to step ST4. In step ST4, the ECU6 stores the cathode pressure and anode pressure at the current time, i.e., the end time of the power generation shutdown process, and then terminates the power generation shutdown process shown in Figure 2.

[0055] During the power generation shutdown process, the ECU6 operates the anode gas supply device 3 and cathode gas supply device 4 according to the above procedure, thereby sealing the anode flow path 21 and cathode flow path 22 when the anode pressure is higher than the cathode pressure. This suppresses the permeation of oxygen from the cathode electrode to the anode electrode in the fuel cell stack 2 during soaking, and thus suppresses the deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking.

[0056] Figures 3A and 3B are flowcharts showing the specific procedure for the anode gas filling process. As mentioned above, in order to suppress the degradation of the fuel cell stack 2 caused by the rise in cathode potential during soaking, it is necessary to maintain a high anode pressure in the fuel cell stack 2 during soaking after the power generation shutdown process is completed. This anode gas filling process is performed by the ECU 6 during the soak of the fuel cell stack 2 in order to maintain a high anode pressure in the fuel cell stack 2 during soaking. The anode gas filling process shown in Figure 3 is performed periodically by the ECU 6 during the soak of the fuel cell stack 2 after the completion of the power generation shutdown process shown in Figure 2. More specifically, after the completion of the power generation shutdown process, the ECU 6 starts the anode gas filling process shown in Figures 3A and 3B in response to being automatically activated during the soak of the fuel cell stack 2 by its built-in RTC.

[0057] First, in step ST11, the ECU6 determines whether the value of the prohibition flag, described later, is "1". The prohibition flag indicates that the execution of the fuel supply process (see step ST15 described later) is prohibited. If the result of the determination in step ST11 is NO, the ECU6 proceeds to step ST12. If it is YES, the anode gas filling process shown in Figures 3A and 3B is terminated without executing the processes in steps ST12 to ST22 described below.

[0058] Next, in step ST12, the ECU6 determines whether the predetermined start conditions for starting the fuel supply process have been met. If the result of the determination in step ST12 is YES, i.e., the start conditions are met, the ECU6 proceeds to step ST13. If the result is NO, i.e., the start conditions are not met, the anode gas filling process shown in Figures 3A and 3B is terminated.

[0059] In the following description, the ECU6 starts the fuel supply process when a predetermined set time has elapsed from the later of the end time of the power generation shutdown process (see step ST3 above) and the end time of the previous fuel supply process (see step ST21 below), but the present invention is not limited to this. For example, the set time may be predetermined, or it may be determined based on the cathode pressure and anode pressure at the end of the power generation shutdown process or the previous fuel supply process (see step ST4 above or step ST22 below). Alternatively, the ECU6 may use the anode pressure at the end of the power generation shutdown process or the previous fuel supply process as a reference, and start the fuel supply process when the current anode pressure drops to a predetermined pressure from this reference.

[0060] Next, in step ST13, the ECU 6, having met the above-mentioned starting conditions, first opens the tank valve 311 and the shut-off valve 321, and then proceeds to step ST14. This fills the hydrogen supply pipe 32 upstream of the injector 322 with high-pressure anode gas.

[0061] Next, in step ST14, the ECU 6 determines whether the tank valve 311 is in the open state. More specifically, the ECU 6 determines whether the tank valve 311 is in the open state by referring to a signal transmitted from, for example, a tank valve sensor (not shown) installed in the hydrogen tank 31. If the result of the determination in step ST14 is YES, the ECU 6 proceeds to step ST15. If the result of the determination in step ST14 is NO, the ECU 6 determines that the tank valve 311 is faulty and proceeds to step ST18.

[0062] In step ST15, the ECU 6 performs a fuel supply process that supplies anode gas to the anode flow path 21 of the fuel cell stack 2 during soaking, and then proceeds to step ST16. More specifically, the ECU 6 drives the injector 322 with the tank valve 311 and shut-off valve 321 open as described above, supplying anode gas from the hydrogen tank 31 to the anode flow path 21 of the fuel cell stack 2. This causes the anode pressure to rise.

[0063] In step ST16, the ECU6 determines whether the anode pressure has reached a predetermined completion threshold pressure, which is at least higher than the current cathode pressure. This completion threshold pressure may be predetermined or determined based on the current cathode pressure. If the result of step ST16 is YES, i.e., if the anode pressure has risen to the completion threshold pressure by executing the fuel supply process, the ECU6 terminates the fuel supply process by stopping the injector 322 and then proceeds to step ST20. If the result of step ST16 is NO, the ECU6 proceeds to step ST17.

[0064] In step ST17, the ECU6 determines whether the fluctuation range of the anode pressure over a predetermined time period is less than or equal to a predetermined completion threshold after the start of the fuel supply process in step ST15. If the result of the determination in step ST17 is NO, that is, if the anode pressure has not yet reached the completion threshold and the fluctuation range of the anode pressure over the predetermined time period is less than or equal to the completion threshold, the ECU6 returns to step ST15 to continue the fuel supply process. As described above, if the above start conditions are met after the completion of the power generation shutdown process, the ECU6 executes the fuel supply process until the anode pressure reaches the completion threshold.

[0065] If the result of step ST17 is YES, that is, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to the completion judgment range, it means that the anode pressure hardly changes even if the injector 322 is opened. This also means that the amount of anode gas remaining in the hydrogen tank 31 has decreased to the point where the pressure on the upstream side of the injector 322 (i.e., the intermediate pressure detected by the intermediate pressure sensor 25) and the pressure on the downstream side (i.e., the anode pressure detected by the anode pressure sensor 28) are approximately equal. Therefore, if the result of step ST17 is YES, the ECU 6 terminates the fuel supply process by stopping the operation of the injector 322 even if the anode pressure is less than the completion judgment pressure, and then moves on to step ST18.

[0066] In step ST18, the ECU 6 sets the value of the prohibit flag to "1" to prohibit the fuel supply process from the next time onward, and then proceeds to step ST19. That is, if the tank valve 311 is malfunctioning (see step ST14 above) or if there is insufficient remaining anode gas until the pressure on the upstream side and the pressure on the downstream side of the injector 322 are approximately equal (see step ST17 above), the ECU 6 sets the value of the prohibit flag to "1" because it is not possible to perform the proper fuel supply process. This value of the prohibit flag is reset to "0" when the cause preventing the proper fuel supply process is removed, i.e., when the repair of the tank valve 311 is completed or when the hydrogen tank 31 is filled with sufficient anode gas.

[0067] In step ST19, the ECU 6 notifies the user that a malfunction has occurred that prevents the proper fuel supply process from being performed, and then proceeds to step ST20. More specifically, if the tank valve 311 is malfunctioning (i.e., the result of the determination in step ST14 above is NO), the ECU 6 notifies the user that the tank valve 311 is malfunctioning by illuminating a predetermined warning light. Also, if the amount of anode gas remaining in the hydrogen tank 31 is insufficient (i.e., the result of the determination in step ST17 above is YES), the ECU 6 notifies the user that the amount of anode gas is insufficient by illuminating a predetermined warning light.

[0068] In step ST20, the ECU 6 seals the anode passage 21 by closing the tank valve 311 and the shut-off valve 321, and then proceeds to step ST21. In step ST21, the ECU 6 stores the current time as the end time of the fuel supply process, and then proceeds to step ST22. In step ST22, the ECU 6 stores the cathode pressure and anode pressure at the present time, i.e., the end time of the fuel supply process, and then terminates the anode gas sealing process shown in Figures 3A and 3B.

[0069] During the anode gas filling and fuel supply processes, the ECU 6 operates the anode gas supply device 3 according to the above procedure, thereby filling the anode gas into the anode flow path 21 during the soak of the fuel cell stack 2. This maintains a high anode pressure in the fuel cell stack 2 during the soak, and consequently suppresses the deterioration of the fuel cell stack 2.

[0070] Figure 4A is a time chart showing a first example of the change in anode pressure achieved by the power generation stop process (see Figure 2) and anode gas sealing process (see Figures 3A and 3B) described above. In the lower part of Figure 4A, the solid line represents the anode pressure (i.e., the pressure downstream of the injector 322 detected by the anode pressure sensor 28), and the dashed line represents the intermediate pressure (i.e., the pressure upstream of the injector 322 detected by the intermediate pressure sensor 25).

[0071] Initially, at time t0, the ECU 6 starts the power generation shutdown process shown in Figure 2, in response to the completion of power generation by the fuel cell stack 2. As described above, at time t0, the ECU 6 initially stops the supply of cathode gas and seals the cathode flow path 22. After sealing the cathode flow path 22 at time t0, the ECU 6 continues to supply anode gas until the anode pressure rises above the cathode pressure to a predetermined target pressure. Therefore, as shown in Figure 4A, the anode pressure continues to rise after time t0.

[0072] Subsequently, at time t1, the ECU 6 closes the shut-off valve 321 and the tank valve 311 in response to the anode pressure reaching the target pressure. As a result, as shown in Figure 4A, after time t1, the anode pressure rises and the intermediate pressure decreases. Then, at time t2, the ECU 6 stops the supply of anode gas by stopping the operation of the injector 322 and closes the purge valve 332. As a result, at time t2, the anode flow path 21 of the fuel cell stack 2 is sealed with the anode pressure higher than the cathode pressure. The ECU 6 also stores time t2, when the anode flow path 21 is sealed, as the end time of the power generation stop process.

[0073] Figure 4A shows the case where the shut-off valve 321 and the tank valve 311 are closed at time t1, and the injector 322 is stopped and the purge valve 332 is closed at time t2, but the present invention is not limited to this. As long as the anode flow path 21 of the fuel cell stack 2 can be sealed when the anode pressure is higher than the cathode pressure, the order in which the shut-off valve 321, the tank valve 311, and the purge valve 332 are closed or the injector 322 is stopped may be any order.

[0074] During the power generation shutdown process, the ECU 6 operates the anode gas supply device 3 and cathode gas supply device 4 according to the procedure described above, thereby sealing the anode flow path 21 and cathode flow path 22 while the anode pressure is higher than the cathode pressure. However, if the soak period of the fuel cell stack 2 is prolonged, the hydrogen sealed in the anode flow path permeates into the cathode flow path and is consumed by reaction with oxygen, causing the anode pressure to gradually decrease as shown in Figure 4A.

[0075] Subsequently, at time t3, ECU6 starts the fuel supply process (see step ST15 in Figure 3A) in response to the fulfillment of the start condition (see step ST12 in Figure 3A). More specifically, at time t3, ECU6 starts the fuel supply process in response to the elapsed time from the end time t2 of the power generation stop process. More specifically, at time t3, ECU6 opens the shut-off valve 321 and the tank valve 311 (see step ST13 in Figure 3A), and after confirming that the tank valve 311 is in the open state (see step ST14 in Figure 3A), starts driving the injector 322 (see step ST15 in Figure 3A). As a result, the anode pressure begins to rise, as shown in Figure 4A.

[0076] After initiating the fuel supply process using the procedure described above, the ECU 6 terminates the fuel supply process by stopping the injector 322 drive at time t4, when the anode pressure reaches the completion determination pressure shown by the dashed line in Figure 4A (see step ST16 in Figure 3A). Subsequently, the ECU 6 closes the shut-off valve 321 and the tank valve 311 (see step ST20 in Figure 3B). This maintains a high anode pressure, thereby suppressing the deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking. The ECU 6 also stores time t4 as the end time of the fuel supply process (see step ST21 in Figure 3B). As a result, if the soaking period of the fuel cell stack 2 is prolonged, the ECU 6 will execute the fuel supply process again when a set time has elapsed from the end time t4 of this fuel supply process. This ensures that the anode pressure remains high even if the soaking period is prolonged.

[0077] Figure 4B is a time chart showing a second example of the change in anode pressure achieved by the power generation shutdown process (see Figure 2) and anode gas sealing process (see Figures 3A and 3B) described above. Figure 4B shows the case where the remaining amount of anode gas in the hydrogen tank 31 is smaller compared to the example shown in Figure 4A. Furthermore, the events that occur between times t10 and t13 in the example shown in Figure 4B are qualitatively the same as the events that occur between times t0 and t3 in the example shown in Figure 4A, so a detailed explanation is omitted.

[0078] At time t13, ECU6 starts the fuel supply process (see step ST15 in Figure 3A) in response to the fulfillment of the start condition (see step ST12 in Figure 3A). More specifically, at time t13, ECU6 starts the fuel supply process in response to the elapsed time from the end time t12 of the power generation stop process. More specifically, at time t13, ECU6 opens the shut-off valve 321 and the tank valve 311 (see step ST13 in Figure 3A), confirms that the tank valve 311 is in the open state (see step ST14 in Figure 3A), and then starts driving the injector 322 (see step ST15 in Figure 3A).

[0079] As described above, the example shown in Figure 4B has less anode gas remaining in the hydrogen tank 31 than the example shown in Figure 4A. Therefore, when the fuel supply process is started at time t13, the anode pressure begins to rise, but the rate of rise is slower than in the example in Figure 4A. Also, because the amount of anode gas remaining in the hydrogen tank 31 is small, the intermediate pressure decreases as the anode pressure rises. Therefore, the anode pressure rises to approximately equal to the intermediate pressure at time t14, and then becomes approximately constant. That is, after time t14, the pressure difference between the upstream and downstream sides of the injector 322 becomes approximately 0, so the anode pressure becomes approximately constant before reaching the completion judgment pressure. Then, at time t15, the ECU 6 determines that the fluctuation range of the anode pressure over a predetermined time is less than or equal to the completion judgment range, and terminates the fuel supply process by stopping the operation of the injector 322 even if the anode pressure is below the completion judgment pressure (see step ST17 in Figure 3A). Subsequently, the ECU 6 closes the shut-off valve 321 and the tank valve 311 (see step ST20 in Figure 3B). Also at this time t15, the ECU 6 sets the value of the prohibition flag to "1" to prohibit the fuel supply process from the next time onward (see step ST18 in Figure 3B), and further informs the user that the remaining amount of anode gas is insufficient.

[0080] The fuel cell system 1 according to this embodiment provides the following effects. (1) When the fuel cell stack 2 stops generating power, the ECU 6 closes the inlet sealing valve 421 and the outlet sealing valve 431, and then stops supplying anode gas to the fuel cell stack 2 when the anode pressure of the fuel cell stack 2 is higher than the cathode pressure, and also closes the purge valve 332, thereby executing a power generation stop process. After the completion of this power generation stop process, if predetermined start conditions are met, the ECU 6 executes a fuel supply process that supplies anode gas to the fuel cell stack 2 until the anode pressure reaches a predetermined completion determination pressure. This makes it possible to maintain the hydrogen partial pressure at the anode electrode of the fuel cell stack 2 at or above a predetermined pressure during soaking, thereby suppressing deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking. Furthermore, after the start of this fuel supply process, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the ECU 6 terminates the ongoing fuel supply process even if the anode pressure is below the completion determination pressure. Therefore, according to the fuel cell system 1, even if the amount of anode gas remaining at the start of the fuel supply process described above is insufficient, the remaining anode gas can be supplied to the fuel cell stack 2 as much as possible. This makes it possible to minimize the deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking, and ultimately contribute to energy efficiency.

[0081] (2) The ECU 6 acquires the pressure detected by the anode pressure sensor 28, which is located on the fuel cell stack 2 side of the injector 322 in the hydrogen supply pipe 32 connecting the hydrogen tank 31 and the inlet side of the anode flow path 21, as the anode pressure. In this way, the fuel cell system 1 determines the timing to terminate the fuel supply process based on the pressure fluctuation range on the lower pressure side of the hydrogen supply pipe 32, which runs from the high-pressure hydrogen tank 31 to the low-pressure fuel cell stack 2. As a result, even if the amount of anode gas remaining in the hydrogen tank 31 is insufficient, the remaining anode gas can be supplied to the fuel cell stack 2 as much as possible, thereby suppressing the deterioration of the fuel cell stack 2 as much as possible.

[0082] (3) If the ECU 6 terminates the fuel supply process before the anode pressure reaches the completion judgment pressure, in other words, if the fuel supply process is terminated because there is not enough anode gas remaining in the hydrogen tank 31, it will prohibit the next fuel supply process and notify the user that there is insufficient anode gas remaining in the hydrogen tank 31. This will minimize the consumption of anode gas in the fuel cell stack 2 during soaking in preparation for the next start of the fuel cell system 1, and will also make the user aware that there is insufficient anode gas remaining.

[0083] (4) The ECU 6 starts the fuel supply process when a set time has elapsed since the end of the power generation shutdown process. In other words, the ECU 6 starts the fuel supply process when a set time has elapsed since the end of the power generation shutdown process, regardless of the remaining amount of anode gas at that time. Therefore, according to the fuel cell system 1, even if the remaining amount of anode gas is insufficient, anode gas can be supplied to the fuel cell stack 2 as much as possible, so that deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking can be suppressed as much as possible.

[0084] (5) The ECU 6 starts the fuel supply process when the anode pressure drops to a predetermined pressure from the end of the power generation shutdown process. In other words, the ECU 6 starts the fuel supply process regardless of the remaining amount of anode gas at the time when the anode pressure drops to a predetermined pressure from the end of the power generation shutdown process. Therefore, according to the fuel cell system 1, even if the remaining amount of anode gas is insufficient, as much anode gas as possible can be supplied to the fuel cell stack 2, so that deterioration of the fuel cell stack 2 caused by the rise in cathode potential during soaking can be suppressed as much as possible.

[0085] <Second Embodiment> Next, a fuel cell system according to the second embodiment of the present invention will be described with reference to the drawings. The fuel cell system according to this embodiment differs from the fuel cell system 1 according to the first embodiment described above in the procedure for anode gas filling. More specifically, the fuel cell system according to this embodiment differs from the fuel cell system 1 according to the first embodiment in the flow up to the start of the fuel supply process in the anode gas filling process.

[0086] Figure 5 is a part of a flowchart showing the specific procedure for the anode gas filling process in the fuel cell system according to this embodiment. Note that the process following Figure 5 is the same as in Figure 3B, so the illustration and detailed explanation are omitted. Also, steps ST31-ST33 and ST35-ST37 in Figure 5 are the same as steps ST11-ST13 and ST15-ST17 in Figure 3A, so a detailed explanation is omitted. In other words, the anode gas filling process according to this embodiment consists of the anode gas filling process shown in Figures 3A and 3B, and a process to determine whether the tank valve 311 is in an open state (see step ST14 in Figure 3A). It differs only in that it does not include [the specified element]. In other words, in the anode gas filling process according to this embodiment, if the start condition is met in step ST32, the fuel supply process is started without checking whether the tank valve 311 is in the open state or not (see step ST35).

[0087] The fuel cell system according to this embodiment provides the following effects. (6) Upstream of the injector 322 in the hydrogen supply pipe 32, there is a small amount of anode gas at a higher pressure than downstream of the injector 322 even before the tank valve 311 is opened (see, for example, times t2-t3 in Figure 4A and times t12-t13 in Figure 4B). Therefore, even if the tank valve 311 is malfunctioning and cannot be opened, by opening the shut-off valve 321 and then driving the injector 322, a portion of the high-pressure anode gas present upstream of the injector 322 in the hydrogen supply pipe 32 can be supplied to the fuel cell stack 2, thereby slightly suppressing the deterioration of the fuel cell stack 2.

[0088] <Third Embodiment> Next, a fuel cell system according to the third embodiment of the present invention will be described with reference to the drawings. The fuel cell system according to this embodiment differs from the fuel cell system 1 according to the first embodiment described above in the procedure for anode gas filling. More specifically, the fuel cell system according to this embodiment differs from the fuel cell system 1 according to the first embodiment in the procedure for anode gas filling.

[0089] Figure 6 is a part of a flowchart showing the specific procedure for the anode gas filling process in the fuel cell system according to this embodiment. The process following Figure 6 is the same as that in Figure 3B, so the illustration and detailed explanation are omitted. Also, the processes in steps ST41 to ST47 in Figure 6 are the same as the processes in steps ST11 to ST17 in Figure 3A, so a detailed explanation is omitted.

[0090] In step ST46, the ECU6 determines that the anode pressure has reached the completion determination pressure, and terminates the fuel supply process by stopping the drive of the injector 322, then proceeds to step ST48. In step ST48, the ECU6 determines whether the upstream pressure detected by the upstream pressure sensor 29, which is installed between the hydrogen tank 31 and the pressure reducing valve 324 in the hydrogen supply pipe 32, is below the prohibition determination pressure, which indicates that the hydrogen tank 31 is low. If the determination result in step ST48 is NO, the ECU6 proceeds to step ST20 in Figure 3B. If the determination result in step ST48 is YES, that is, if the upstream pressure at the end of the fuel supply process was below the prohibition determination pressure, the ECU6 proceeds to step ST18 in Figure 3B to prohibit the next fuel supply process.

[0091] The fuel cell system according to this embodiment provides the following effects. (7) At the end of the fuel supply process, if the upstream pressure detected by the upstream pressure sensor 29 installed between the hydrogen tank 31 and the pressure reducing valve 324 in the hydrogen supply pipe 32 is below a predetermined prohibition judgment pressure, the ECU 6 prohibits the execution of the next fuel supply process. This prevents an excessive drop in pressure inside the hydrogen tank 31 during soaking, thereby protecting the hydrogen tank 31.

[0092] <Fourth Embodiment> Next, a fuel cell system according to the fourth embodiment of the present invention will be described with reference to the drawings. The fuel cell system according to this embodiment differs from the fuel cell system 1 according to the first embodiment described above in the procedure for anode gas filling. More specifically, the fuel cell system according to this embodiment differs from the fuel cell system according to the third embodiment in the flow up to the start of the fuel supply process in the anode gas filling process.

[0093] Figure 7 is a part of a flowchart showing the specific procedure for the anode gas filling process in the fuel cell system according to this embodiment. Note that the process following Figure 7 is the same as that in Figure 3B, so the illustration and detailed explanation are omitted. Also, the processes in steps ST51 to ST54 and ST56 to ST59 in Figure 7 are the same as the processes in steps ST41 to ST44 and ST45 to ST48 in Figure 6, so a detailed explanation is omitted.

[0094] In step ST54, the ECU6 confirms that the tank valve 311 is open. Then, in step ST55, it determines whether the upstream pressure detected by the upstream pressure sensor 29 is below the prohibition judgment pressure. If the result of the determination in step ST55 is NO, the ECU6 proceeds to step ST56 and starts the fuel supply process. If the result of the determination in step ST55 is YES, that is, if the upstream pressure after opening the tank valve 311 is below the prohibition judgment pressure, the ECU6 proceeds to step ST18 in Figure 3B to prohibit the current and next fuel supply processes.

[0095] The fuel cell system according to this embodiment provides the following effects. (8) If the upstream pressure immediately before starting the fuel supply process, more specifically after opening the tank valve 311, is below the prohibition judgment pressure, the ECU 6 will prohibit the execution of the current and next fuel supply processes. This prevents an excessive drop in pressure inside the hydrogen tank 31 during soaking, thereby protecting the hydrogen tank 31.

[0096] Although one embodiment of the present invention has been described above, the present invention is not limited thereto. Within the scope of the spirit of the present invention, the details of the configuration may be modified as appropriate. [Explanation of Symbols]

[0097] 1…Fuel cell system 2…Fuel cell stack (fuel cell) 21... Anode channel 22... Cathode channel 25…Medium pressure sensor 27… Cathode pressure sensor 28…Anode pressure sensor (first pressure detection device) 29…Upstream pressure sensor (second pressure detection device) 3…Anode gas supply device 31…Hydrogen tank (anode gas supply source) 311... Tank valve 32…Hydrogen supply pipe (anode gas supply line) 321...Shut-off valve 322... Injector 324... Pressure Reducing Valve 33…Hydrogen discharge pipe 332... Purge valve (anode discharge valve) 34…Hydrogen reflux tube (anode gas reflux channel) 4… Cathode gas supply device 42... Air supply pipe 421... Inlet sealing valve (cathode sealing valve) 43... Air exhaust pipe 431... Outlet sealing valve (cathode sealing valve) 5…Cooling system 6…ECU (Control Unit) 7…Power circuit

Claims

1. A fuel cell system comprising a fuel cell that generates electricity when anode gas and cathode gas are supplied, A cathode gas supply device that supplies cathode gas to the cathode flow path of the fuel cell, an anode gas supply device that supplies anode gas to the anode flow path of the fuel cell, The system comprises a cathode gas supply device and a control means for operating the anode gas supply device, The cathode gas supply device includes cathode sealing valves provided on the inlet and outlet sides of the cathode flow path. The anode gas supply device includes an anode discharge valve provided on the outlet side of the anode flow path, The control means is After closing the cathode sealing valve when the power generation of the fuel cell is stopped, the supply of anode gas to the fuel cell is stopped and the anode discharge valve is closed while the anode pressure of the fuel cell is higher than the cathode pressure, and the stopping process is performed. If predetermined start conditions are met after the completion of the stop process, the system is configured to perform a fuel supply process that supplies anode gas to the fuel cell until the anode pressure reaches a predetermined completion determination pressure. The fuel cell system is characterized in that, after the start of the fuel supply process, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the control means terminates the fuel supply process even if the anode pressure is less than the completion determination pressure.

2. The anode gas supply device comprises an anode gas supply source, an anode gas supply path connecting the anode gas supply source and the inlet side of the anode flow path, an injector provided in the anode gas supply path, and an anode gas return path connecting the outlet side of the anode flow path and the anode gas supply path downstream of the injector. The fuel cell system according to claim 1, characterized in that the control means acquires the pressure detected by a first pressure detection device provided between the injector and the fuel cell in the anode gas supply path as the anode pressure.

3. The fuel cell system according to claim 2, characterized in that if the fuel supply process is terminated before the anode pressure reaches the completion determination pressure, the control means prohibits the next fuel supply process and notifies the user that the anode gas supply source is in a state of insufficient remaining anode gas.

4. The fuel cell system according to any one of claims 1 to 3, characterized in that the control means starts the fuel supply process with the start condition being that a predetermined time has elapsed from the end of the stop process.

5. The fuel cell system according to any one of claims 1 to 3, characterized in that the control means starts the fuel supply process with the start condition being that the anode pressure drops to a predetermined pressure from the end of the stop process.

6. The anode gas supply device further comprises a pressure reducing valve provided between the injector and the anode gas supply source in the anode gas supply path, The fuel cell system according to claim 2 or 3, characterized in that the control means prohibits the next fuel supply process if, at the end of the fuel supply process, the pressure detected by a second pressure detection device provided between the anode gas supply source and the pressure reducing valve is less than a predetermined prohibition judgment pressure.

7. A control method for a fuel cell system comprising: a fuel cell that generates electricity when anode gas and cathode gas are supplied; a cathode gas supply device that supplies cathode gas to the cathode channel of the fuel cell; and an anode gas supply device that supplies anode gas to the anode channel of the fuel cell, The cathode gas supply device includes cathode sealing valves provided on the inlet and outlet sides of the cathode flow path. The anode gas supply device includes an anode discharge valve provided on the outlet side of the anode flow path, The first step involves closing the cathode sealing valve when the fuel cell stops generating power, then stopping the supply of anode gas to the fuel cell while the anode pressure of the fuel cell is higher than the cathode pressure, and closing the anode discharge valve. If predetermined start conditions are met after the completion of the first step, the second step includes supplying anode gas to the fuel cell until the anode pressure reaches a predetermined completion determination pressure, A control method for a fuel cell system, characterized in that, after the start of the second step, if the fluctuation range of the anode pressure over a predetermined time is less than or equal to a predetermined completion determination range, the second step is terminated even if the anode pressure is less than the completion determination pressure.

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