Fuel Cell Systems

Abstract

To provide a technique by which a gas leakage check is effectively performed to reduce a time required to start a fuel cell system in which a plurality of fuel cell (FC) stacks are connected in parallel.SOLUTION: A controller of a fuel cell system disclosed in the present specification performs the following processes for: (1) starting both of two FC stacks when a gas concentration in a housing is lower than a first concentration, the housing accommodating the two FC stacks therein; (2) maintaining both of the two FC stacks stopped when a measured value of a gas sensor is higher than a second concentration which is higher than the first concentration; and (3) supplying a fuel gas to a high-temperature FC stack while maintaining supply of the fuel gas to a low-temperature FC stack stopped when the gas concentration is equal to or more than the first concentration and equal to or less than the second concentration, thereafter stopping supply of the fuel gas when a pressure in the high-temperature FC stack reaches a predetermined pressure threshold, and thereafter starting the high-temperature FC stack when the pressure in the high-temperature FC stack after a predetermined time is higher than a predetermined pressure lower limit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a fuel cell system in which a plurality of fuel cell stacks are connected in parallel. [Background technology]

[0002] Patent Documents 1 and 2 disclose fuel cell systems equipped with multiple fuel cell stacks connected in parallel. In the system of Patent Document 1, each fuel cell stack is equipped with a leak detection unit that detects fuel gas leakage. The leak detection unit determines whether or not there is a fuel gas leak from fluctuations in the fuel gas pressure. In the system of Patent Document 1, all of the leak detection units are activated simultaneously prior to starting up the fuel cell stacks. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-149347 A [Patent Document 2] International Publication No. 2017 / 010069 Summary of the Invention [Problem to be solved by the invention]

[0004] In the fuel cell system of Patent Document 1, the fuel cell stacks are started up after all leak detection units have confirmed that there are no fuel gas leaks. It takes a considerable amount of time to fill all fuel cell stacks with fuel gas at a specified pressure. Conventional fuel cell systems take a long time to start supplying power after receiving a startup command. This specification relates to a fuel cell system in which multiple fuel cell stacks are connected in parallel, and provides a technology for efficiently checking for gas leaks and shortening the startup time of the fuel cell system. [Means for solving the problem]

[0005] The fuel cell system disclosed in this specification includes two fuel cell stacks connected in parallel. Of the two fuel cell stacks, the one with the higher temperature is called the high-temperature fuel cell stack, and the one with the lower temperature is called the low-temperature fuel cell stack. After the gas leak check of the high-temperature fuel cell stack is completed, the high-temperature fuel cell stack is started before the gas leak check of the low-temperature fuel cell stack. If the pressure drop in the fuel cell stack after a predetermined time is small, the controller determines that there is no gas leak. In general, the high-temperature gas (gas in the high-temperature container) has a higher pressure than the low-temperature gas (gas in the low-temperature container). That is, in two fuel cell stacks receiving a supply of fuel gas, the fuel gas pressure increases more quickly in the high-temperature fuel cell stack than in the low-temperature fuel cell stack. The fuel cell stack in which the fuel gas pressure increases more quickly can complete the gas leak check sooner. The fuel cell system disclosed in this specification can quickly start supplying power after receiving a start command.

[0006] The fuel cell system disclosed in this specification includes two fuel cell stacks connected in parallel, a fuel tank that supplies fuel gas to the two fuel cell stacks, a housing that houses the two fuel cell stacks, a gas sensor that measures the fuel gas concentration in the housing, and a controller. In response to a start-up command, the controller starts up the fuel cell stack that is not leaking gas.

[0007] When the controller receives a start-up command, it executes the following process: (1) The controller starts up both of the two fuel cell stacks if the gas sensor measurement value is below a first concentration. (2) The controller does not start up either fuel cell stack if the gas sensor measurement value is above a second concentration that is higher than the first concentration. (3) If the gas sensor measurement value is equal to or greater than the first concentration and equal to or less than the second concentration, the controller compares the temperatures of the two fuel cell stacks and supplies fuel gas to the high-temperature fuel cell stack while stopping the supply of fuel gas to the low-temperature fuel cell stack. The controller stops the supply of fuel gas when the pressure in the high-temperature fuel cell stack reaches a predetermined pressure threshold. If the pressure in the high-temperature fuel cell stack after a predetermined time period is above a predetermined lower pressure limit, the controller starts up the high-temperature fuel cell stack.

[0008] In the above fuel cell system, once it is confirmed that there are no gas leaks in the high-temperature fuel cell stack, the high-temperature fuel cell stack is started up without waiting for the completion of the gas leak check of the low-temperature fuel cell stack. As mentioned above, the gas pressure in the high-temperature container (high-temperature fuel cell stack) increases more quickly than the gas pressure in the low-temperature container (low-temperature fuel cell stack). A gas leak check of the high-temperature fuel cell stack is performed first, and if there are no gas leaks, the high-temperature fuel cell stack is started up. This process allows power supply to begin quickly after receiving a startup command.

[0009] This specification also discloses another embodiment of a fuel cell system that does not necessarily require a gas sensor in the housing. The fuel cell system includes two fuel cell stacks connected in parallel, a fuel tank that supplies fuel gas to the two fuel cell stacks, and a controller. In response to a start-up command, the controller starts up the fuel cell stack that is not leaking gas.

[0010] When the controller receives a start-up command, it executes the following process. (1) The controller compares the temperatures of the two fuel cell stacks. It supplies fuel gas to the high-temperature fuel cell stack while stopping the supply of fuel gas to the low-temperature fuel cell stack. (2) The controller stops the supply of fuel gas to the high-temperature fuel cell stack when the pressure in the high-temperature fuel cell stack reaches a predetermined first pressure threshold. If the pressure in the high-temperature fuel cell stack after a predetermined time (first pressure) is above a predetermined first pressure lower limit, the controller starts the high-temperature fuel cell stack and starts the supply of fuel gas to the low-temperature fuel cell stack. (3) If the first pressure is below the first pressure lower limit, the controller starts the supply of fuel gas to the low-temperature fuel cell stack without starting the high-temperature fuel cell stack. (4) The controller stops the supply of fuel gas to the low-temperature fuel cell stack when the pressure in the low-temperature fuel cell stack reaches a predetermined second pressure threshold, and if the pressure in the low-temperature fuel cell stack after a predetermined time (second pressure) is above a predetermined second pressure lower limit, the controller starts the low-temperature fuel cell stack. (5) The controller will not start up the low-temperature fuel cell stack if the second pressure is below a second lower pressure limit.

[0011] In the second fuel cell system, if it is determined in the above process (2) that there is no gas leak in the high-temperature fuel cell stack, the high-temperature fuel cell stack is started up before checking for gas leaks in the low-temperature fuel cell stack. A gas leak check is performed on the high-temperature fuel cell stack first, and if there is no gas leak, the high-temperature fuel cell stack is started up. This process makes it possible to start supplying power quickly after receiving a start-up command.

[0012] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram of a fuel cell system according to a first embodiment. [Diagram 2] 13 is a flowchart of a startup process. [Diagram 3] 13 is a flowchart of the startup process (continuation of Figure 2). [Figure 4] 13 is a flowchart of the startup process (continuation of FIG. 3). [Diagram 5] FIG. 11 is a block diagram of a fuel cell system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) A fuel cell system 2 of the first embodiment will be described. In the following, for ease of description, "fuel cell" may be abbreviated as FC. FIG. 1 shows a block diagram of the FC system 2 (fuel cell system 2). A controller 8 and various devices (valves 11a, 11b, 13a, 13b, air compressors 14a, 14b, pressure sensors 12a, 12b, gas sensor 21, temperature sensors 17a, 17b, boost converter 16, inverter 6, etc.) are connected via communication lines, but the communication lines are not shown in the figure.

[0015] The FC system 2 has two FC stacks (a first FC stack 10a and a second FC stack 10b), and each FC stack generates electricity. The capacity of the first FC stack 10a is the same as that of the second FC stack 10b. "Capacity of the FC stack" refers to the size of the space inside the FC stack. In the following, the first FC stack 10a and the second FC stack 10b may be referred to as FC stack 10 when there is no distinction between them.

[0016] Each FC stack 10 is associated with a boost converter 16. The input terminal of the boost converter 16 is connected to the output terminal of the FC stack 10, and the output terminal of the boost converter 16 is connected to the DC terminal of the inverter 6. The boost converter 16 boosts the DC power generated by the FC stack 10 and supplies it to the inverter 6. The inverter 6 converts the boosted DC power into AC power. A system output terminal 7 is connected to the AC terminal of the inverter 6, and the power generated by the FC stack 10 is supplied from the system output terminal 7 to other devices.

[0017] Fuel gas (hydrogen gas) is supplied to the FC stack 10 from a fuel tank 3 through a fuel supply pipe 4. A fuel valve 11a (11b) is connected to the fuel supply pipe 4, and the flow rate of the fuel gas supplied to the first FC stack 10a (second FC stack 10b) can be adjusted by adjusting the opening of the fuel valve 11a (11b). The fuel valves 11a, 11b are sometimes called injectors.

[0018] A pressure sensor 12a (12b) is connected downstream of the fuel valve 11a (11b), and the pressure measured by the pressure sensor 12a (12b) is equal to the pressure inside the first FC stack 10a (second FC stack 10b). While the FC stack 10 is generating power, the controller 8 controls the opening of the fuel valves 11a, 11b so that the measurement value of the pressure sensor 12a (12b) is maintained within an appropriate range. The fuel valves 11a, 11b may be referred to as fuel valve 12 when there is no need to distinguish between them, and the pressure sensors 12a, 12b may be referred to as pressure sensor 12 when there is no need to distinguish between them.

[0019] Air (oxygen) is supplied to the FC stack 10 through an air supply pipe 5. The air supply pipe 5 is equipped with an air compressor 14a (14b) and an air valve 13a (13b), and air is sent to the first FC stack 10a (second FC stack 10b) by the air compressor 14a (14b). The amount of air (oxygen) supplied to the first FC stack 10a (second FC stack 10b) is adjusted by the output of the air compressor 14a (14b) and the opening of the air valve 13a (13b). When there is no need to distinguish between the air compressors 14a and 14b, they may be referred to as air compressor 14.

[0020] In the FC stack 10, fuel gas (hydrogen) reacts with air (oxygen) to generate electricity. The gas after the reaction (exhaust gas) is sent to a gas-liquid separator 33 via an exhaust gas pipe 31. In the gas-liquid separator 33, hydrogen gas not used in the reaction is separated from the exhaust gas. The separated hydrogen gas is returned to the fuel supply pipe 4 via a return pipe 4a. The remaining exhaust gas and water are mixed with air exhausted from the FC stack 10 via an exhaust air pipe 32, and are released into the atmosphere via a muffler 35. An exhaust valve 34 is provided at the outlet of the gas-liquid separator 33. By adjusting the opening of the exhaust valve 34, the fuel gas is diluted with air until the fuel gas concentration drops to an appropriate concentration. When the fuel gas remaining in the FC stack 10 is discharged, the fuel gas is diluted with air sent from the exhaust air pipe 32 to a predetermined safe concentration before being released into the atmosphere.

[0021] The first FC stack 10a and the second FC stack 10b are housed in a housing 20. The housing 20 is provided with a gas sensor 21 that measures the fuel gas concentration within the housing.

[0022] A first temperature sensor 17a is attached to the first FC stack 10a, and a second temperature sensor 17b is attached to the second FC stack 10b. When the first temperature sensor 17a and the second temperature sensor 17b are not distinguished from each other, they are referred to as temperature sensor 17. The temperature sensor 17 measures the temperature of the FC stack 10. The temperature of the FC stack 10 is also an approximation of the gas temperature inside the FC stack 10. In other words, the measurement value of the temperature sensor 17 may be regarded as the temperature of the gas inside the FC stack 10.

[0023] Measurement values ​​of sensors such as the gas sensor 21, the pressure sensor 12, and the temperature sensor 17 are sent to the controller 8. As described above, the controller 8 is connected to actuators such as the air compressor 14a, and devices such as the FC stack 10 and the boost converter 16 via communication lines, and the controller 8 controls the actuators and devices.

[0024] The startup process of the FC system 2 will now be described. When the controller 8 receives an external startup command, it starts up the FC stack 10 and prepares to supply power from the system output terminal 7. Prior to starting up the FC stack 10, the controller 8 checks to ensure safety that there is no fuel gas leakage in the FC stack 10. For ease of explanation, below, "fuel gas leakage" may be simply referred to as "gas leakage".

[0025] The controller 8 first checks whether the inside of the housing 20 is filled with fuel gas using the measurement value (fuel gas concentration inside the housing) of the gas sensor 21. If the fuel gas concentration inside the housing 20 is below a predetermined first concentration, it can be confirmed that there is no gas leakage in all of the FC stacks 10 without checking for gas leakage in each of the FC stacks 10. By installing the gas sensor 21 inside the housing, the gas leakage check can be completed in a short time compared to checking for gas leakage in each of the FC stacks 10. In other words, the time from receiving a startup command to being ready to supply power can be shortened.

[0026] If the fuel gas concentration inside the housing 20 exceeds a predetermined second concentration, the controller 8 determines that it is not suitable to start up the FC stacks 10, and stops the process without starting up any of the FC stacks 10. The second concentration is set to a value higher than the first concentration.

[0027] When the fuel gas concentration inside the housing 20 is equal to or higher than the first concentration and equal to or lower than the second concentration, the FC stacks 10 that are not leaking gas may be started. In this case, the controller 8 checks for gas leaks in each of the FC stacks 10. The procedure for checking for gas leaks in the FC stacks 10 will be described below.

[0028] The controller 8 compares the temperatures of the two FC stacks 10. The temperature of the FC stack 10a (10b) is measured by a temperature sensor 17a (17b). For convenience, below, of the two FC stacks 10, the one with the higher temperature is referred to as the high-temperature FC stack, and the one with the lower temperature is referred to as the low-temperature FC stack.

[0029] The controller 8 first checks for gas leaks in the high-temperature FC stack, and if it confirms that there are no gas leaks, it starts up the high-temperature FC stack without waiting for the completion of the gas leak check for the low-temperature FC stack. Generally, if the volume is the same, the higher the temperature, the higher the internal gas pressure. Gas leaks are detected in the following procedure. The controller 8 fills the FC stack 10 with fuel gas up to a predetermined pressure threshold, and checks the fuel gas pressure after a predetermined time. If the fuel gas pressure after the predetermined time is below a predetermined lower pressure limit, the controller 8 determines that gas is leaking.

[0030] The internal gas pressure of a high-temperature FC stack increases more quickly than that of a low-temperature FC stack. By checking the high-temperature FC stack for gas leaks before checking the low-temperature FC stack, the time from when a start-up command is received until the stack is ready to supply power can be shortened.

[0031] The startup process executed by the controller 8 will be described in detail with reference to the flowcharts of Figures 2 to 4. Note that "FCS" in Figures 3 and 4 stands for fuel cell stack.

[0032] The controller 8 uses the gas sensor 21 to measure the fuel gas concentration inside the housing 20 (step S2). If the fuel gas concentration exceeds the second concentration, the controller 8 determines that it is not suitable for starting up the FC stack 10, notifies the user of a gas leak, and ends the process (steps S3: YES, S4). The notification of the gas leak is sent to a display 9 (see FIG. 1) connected to the controller 8, or to the user's terminal. A message indicating the occurrence of a gas leak is displayed on the display 9 or the user's terminal that has received the notification. If the fuel cell system 2 is installed in an automobile, a message indicating the occurrence of a gas leak is displayed on the instrument panel.

[0033] If the fuel gas concentration does not exceed the second concentration, the controller 8 compares the fuel gas concentration inside the housing 20 with the first concentration (steps S3: NO, S5). As described above, the second concentration is set to a concentration that is not suitable for starting up the FC stack 10, and the first concentration is set to a value lower than the second concentration. The first concentration is set to a value that indicates the possibility that a gas leak has occurred in either of the two FC stacks 10.

[0034] If the fuel gas concentration is below the first concentration (step S5: YES), the controller 8 determines that there is no gas leak in either of the two FC stacks 10. In this case, the controller 8 opens fuel valves 11a and 11b to start the supply of fuel gas to the two FC stacks 10, also starts the supply of air, and starts up the two FC stacks 10 (step S6). When step S6 is executed, preparations for power supply are complete. After step S6, the controller 8 adjusts the amounts of fuel gas and air (oxygen) supplied to the FC stacks 10 so that power can be supplied according to demand.

[0035] On the other hand, if the fuel gas concentration is equal to or higher than the first concentration and equal to or lower than the second concentration (steps S3: NO, S5: NO), the controller 8 compares the temperatures of the two FC stacks 10 (FIG. 3, step S11). As described above, of the two FC stacks 10, the FC stack with the higher temperature is referred to as the high-temperature FC stack, and the FC stack with the lower temperature is referred to as the low-temperature FC stack. In FIGS. 3 and 4, the high-temperature FC stack is referred to as the high-temperature FCS, and the low-temperature FC stack is referred to as the low-temperature FCS.

[0036] The controller 8 first checks for gas leaks in the high-temperature FC stack. The flowchart in Fig. 3 corresponds to the gas leak check in the high-temperature FC stack.

[0037] The controller 8 first opens the fuel valve 11 that supplies fuel gas to the high-temperature FC stack. The supply of fuel gas to the high-temperature FC stack is started (step S12). At this time, the fuel valve 11 that supplies fuel gas to the low-temperature FC stack remains closed. In other words, no fuel gas is supplied to the low-temperature FC stack. The controller 8 continues to supply fuel gas until the pressure inside the high-temperature FC stack reaches a first pressure threshold (step S13). The first pressure threshold is set to a value at which the high-temperature FC stack can generate power. The pressure inside the high-temperature FC stack is measured by a pressure sensor 12a.

[0038] When the pressure inside the high-temperature FC stack reaches the first pressure threshold, the controller 8 closes the fuel valve 11 and stops the supply of fuel to the high-temperature FC stack. The controller then waits for a predetermined time (step S13). The predetermined time is set to, for example, one minute. If the pressure inside the high-temperature FC stack has dropped significantly after the predetermined time, it is determined that a gas leak has occurred in the high-temperature FC stack. Conversely, if the pressure inside the high-temperature FC stack has not dropped significantly even after the predetermined time has passed, it is determined that no gas leak has occurred.

[0039] After waiting for a certain period of time, the controller 8 measures the pressure inside the high-temperature FC stack again with the pressure sensor 12 (step S14). For convenience of explanation, the pressure inside the high-temperature FC stack after the predetermined time has elapsed is referred to as the first FC pressure.

[0040] If the first FC pressure is above the predetermined first pressure lower limit value, the controller 8 determines that no gas leak is occurring in the high-temperature FC stack. In this case, the controller 8 resumes fuel supply to the high-temperature FC stack and starts up the high-temperature FC stack (steps S15: YES, S16). When step S16 is executed, it becomes possible for the high-temperature FC stack to supply power. After step S16, the controller 8 adjusts the amounts of fuel gas and air (oxygen) supplied to the high-temperature FC stack so that power can be supplied according to demand. Note that at this point, the low-temperature FC stack has not yet started up.

[0041] If the first FC pressure is below the first pressure lower limit, the controller 8 notifies the gas leak of the high-temperature FC stack (step S15: NO, S17). The notification in step S17 is sent from the controller 8 to the display 9 or the user's terminal, similar to the notification in step S4.

[0042] Incidentally, since the gas concentration inside the housing 20 is equal to or lower than the second concentration (step S3: NO), even if a gas leak occurs in the low-temperature FC stack, the high-temperature FC stack may be started up.

[0043] Next, the controller 8 executes a gas leak check process for the low-temperature FC stack. The flow chart of Fig. 4 shows the gas leak check process for the low-temperature FC stack.

[0044] The gas leak check process for the low-temperature FC stack is the same as that for the high-temperature FC stack.

[0045] The controller 8 opens the fuel valve 11 that supplies fuel gas to the low-temperature FC stack. The controller 8 starts the supply of fuel gas to the low-temperature FC stack (step S22). The controller 8 continues the supply of fuel gas until the pressure inside the low-temperature FC stack reaches a second pressure threshold (step S23). The second pressure threshold is set to a value at which the low-temperature FC stack can generate power. The pressure inside the low-temperature FC stack is measured by the pressure sensor 12b.

[0046] Additionally, if the first FC stack 10a and the second FC stack 10b have the same volume and performance, the second pressure threshold may be equal to the first pressure threshold.

[0047] When the pressure inside the low-temperature FC stack reaches the second pressure threshold, the controller 8 closes the fuel valve 11 and stops the fuel supply to the low-temperature FC stack. Then, the controller waits for a predetermined time (step S23). If the pressure inside the low-temperature FC stack has decreased considerably after waiting for the predetermined time, it is determined that a gas leak has occurred in the low-temperature FC stack. Conversely, if the pressure inside the low-temperature FC stack has not decreased significantly even after the predetermined time has elapsed, it is determined that no gas leak has occurred.

[0048] After waiting for a certain period of time, the controller 8 measures the pressure inside the low-temperature FC stack again with the pressure sensor 12 (step S24). For convenience of explanation, the pressure inside the low-temperature FC stack after the lapse of a certain period of time is referred to as the second FC pressure.

[0049] If the low-temperature FC pressure is above the predetermined second lower limit pressure, the controller 8 resumes fuel supply to the low-temperature FC stack and starts up the low-temperature FC stack (steps S25: YES, S26). When step S26 is executed, power can also be supplied from the low-temperature FC stack. After step S26, the controller 8 adjusts the amounts of fuel gas and air (oxygen) supplied to the high-temperature FC stack and the low-temperature FC stack so that power according to demand can be supplied.

[0050] In addition, when the first FC stack 10a and the second FC stack 10b have the same volume and performance, the second pressure lower limit value may be equal to the first pressure lower limit value.

[0051] On the other hand, if the second FC pressure is below the second pressure lower limit, the controller 8 notifies the user of a gas leak from the low-temperature FC stack (step S25: NO, S27). The notification in step S27 is sent from the controller 8 to the display 9 or the user's terminal, similar to the notification in step S4.

[0052] When steps S16 and S26 are executed, the FC system 2 generates power using the two FC stacks 10. When the determination in step S15 is NO and step S26 is executed, the FC system 2 generates power using only the low-temperature FC stack. At this time, the FC system 2 cannot supply large amounts of power, but can supply power within the capacity of the low-temperature FC stack. When step S16 is executed and the determination in step S25 is NO, the FC system 2 generates power using only the high-temperature FC stack. At this time, the FC system 2 cannot supply large amounts of power, but can supply power within the capacity of the high-temperature FC stack.

[0053] As described above, the FC system 2 first checks the gas concentration inside the housing, and if it determines that no gas leak has occurred, it immediately starts up the two FC stacks 10a, 10b. After receiving a start-up command, the FC system 2 quickly becomes ready to supply power.

[0054] When the gas concentration inside the housing is equal to or higher than the first concentration and equal to or lower than the second concentration, a gas leak check is performed on the high-temperature FC stack first. Because the high-temperature FC stack has a higher temperature than the low-temperature FC stack, the fuel gas pressure increases quickly. The controller 8 fills the FC stack with fuel gas up to a predetermined pressure threshold, and performs a gas leak check by detecting a drop in gas pressure after a predetermined time. In such a gas leak check process, the higher the temperature of the FC stack, the quicker the gas leak check can be completed. Because the FC system 2 checks for gas leaks in the high-temperature FC stack first, the time from when it receives a startup command until it is ready to supply power is short.

[0055] If a gas leak is detected in the high-temperature FC stack (step S15: NO), the controller 8 dilutes the fuel gas in the high-temperature FC stack with air and releases it to the atmosphere. Similarly, if a gas leak is detected in the low-temperature FC stack (step S25: NO), the controller 8 dilutes the fuel gas in the low-temperature FC stack with air and releases it to the atmosphere.

[0056] Second embodiment An FC system 102 of a second embodiment will be described with reference to Fig. 5. The FC system 102 has the same structure as the FC system 2 of the first embodiment, except that it does not have the gas sensor 21. Therefore, the FC system 102 does not perform gas leak detection using a gas sensor. The controller 108 of the FC system 102 does not execute the process of Fig. 2, but performs a gas leak check by the processes of Figs. 3 and 4.

[0057] When the controller 108 receives a start-up command, it executes the following process. (1) It compares the temperatures of the two FC stacks 10. It starts the supply of fuel gas to the high-temperature FC stack while stopping the supply of fuel gas to the low-temperature FC stack (step S12). (2) When the pressure in the high-temperature FC stack reaches a predetermined first pressure threshold, it stops the supply of fuel gas to the high-temperature FC stack and waits for a predetermined time (step S13). After waiting for the predetermined time, if the pressure in the high-temperature FC stack (first FC pressure) is above the first pressure lower limit, it starts the high-temperature FC stack (steps S15: YES, S16). It then starts the supply of fuel gas to the low-temperature FC stack (step S22). (3) If the first FC pressure is below the first pressure lower limit, it starts the supply of fuel gas to the low-temperature FC stack without starting the high-temperature FC stack (steps S15: NO, S17, S22). (4) When the pressure in the low-temperature FC stack reaches a second pressure threshold, it stops the supply of fuel gas to the low-temperature FC stack and waits for a predetermined time (step S23). After waiting for a predetermined time, if the pressure in the low-temperature FC stack (second FC pressure) is above a predetermined second pressure lower limit value, the low-temperature FC stack is started (step S25: YES, S26). (5) If the second FC pressure is below the second pressure lower limit value, the low-temperature FC stack is not started (step S25: NO, S27).

[0058] The FC system 102 of the second embodiment also checks the high-temperature FC stack for gas leaks before checking the low-temperature FC stack. Once it is confirmed that there is no gas leak in the high-temperature FC stack, the high-temperature FC stack is started up without waiting for the completion of the gas leak check for the low-temperature FC stack. The FC system 102 of the second embodiment can also quickly start supplying power after receiving a startup command.

[0059] The following points should be noted regarding the technology described in the embodiments. The FC system disclosed in this specification may have three or more FC stacks connected in parallel. All of the FC stacks have the same capacity. Among the three or more FC stacks, a gas leak check is performed on the FC stack with the highest temperature before the other FC stacks.

[0060] In the description of the embodiment, the expression "greater than" may be replaced with "equal to or greater than." Similarly, the expression "less than" may be replaced with "equal to or less than." In other words, in determining an inequality in a flowchart, the case where the right side and the left side are equal may be included as either "YES" or "NO."

[0061] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0062] 2, 102: fuel cell system 3: fuel tank 4: fuel supply pipe 4a: return pipe 5: air supply pipe 6: inverter 7: system output terminal 8, 108: controller 9: display 10, 10a, 10b: FC stack 11a, 11b, 131, 13b: valve 12a, 12b: pressure sensor 14a, 14b: air compressor 16: boost converter 17a, 17b: temperature sensor 20: housing 21: gas sensor 31: exhaust gas pipe 32: exhaust air pipe 33: gas-liquid separator 34: exhaust valve 35: muffler

Claims

1. two fuel cell stacks connected in parallel; a fuel tank for supplying fuel gas to the two fuel cell stacks; a housing for housing the two fuel cell stacks; a gas sensor that measures a fuel gas concentration in the housing; a controller that starts up the fuel cell stack in response to a start-up command; Equipped with The controller includes: (1) starting up both fuel cell stacks when the measured value of the gas sensor is below a first concentration; (2) when the measured value is greater than a second concentration that is higher than the first concentration, neither of the two fuel cell stacks is started; (3) When the measured value is equal to or greater than the first concentration and equal to or less than the second concentration, the temperatures of the two fuel cell stacks are compared, and the fuel gas supply to the high temperature fuel cell stack is supplied while the supply of fuel gas to the low temperature fuel cell stack is stopped, and when the pressure in the high temperature fuel cell stack reaches a predetermined pressure threshold, the supply of the fuel gas is stopped, and when the pressure in the high temperature fuel cell stack after a predetermined time period exceeds a predetermined lower pressure limit, the high temperature fuel cell stack is started. Fuel cell system.

2. two fuel cell stacks connected in parallel; a fuel tank for supplying fuel gas to the two fuel cell stacks; a controller for starting up the two fuel cell stacks in response to a start-up command; Equipped with The controller includes: (1) comparing the temperatures of the two fuel cell stacks, and supplying the fuel gas to the high temperature fuel cell stack while stopping the supply of the fuel gas to the low temperature fuel cell stack; (2) when the pressure in the high-temperature fuel cell stack reaches a predetermined first pressure threshold, the supply of the fuel gas to the high-temperature fuel cell stack is stopped, and if the pressure (first pressure) in the high-temperature fuel cell stack after a predetermined time period exceeds a predetermined first pressure lower limit value, the high-temperature fuel cell stack is started up, and the supply of the fuel gas to the low-temperature fuel cell stack is started; (3) if the first pressure is below the first pressure lower limit, starting the supply of the fuel gas to the low-temperature fuel cell stack without starting up the high-temperature fuel cell stack; (4) when the pressure in the low-temperature fuel cell stack reaches a predetermined second pressure threshold, the supply of the fuel gas to the low-temperature fuel cell stack is stopped, and when the pressure in the low-temperature fuel cell stack after a predetermined time (the second pressure) exceeds a predetermined second pressure lower limit value, the low-temperature fuel cell stack is started; (5) when the second pressure is lower than the second pressure lower limit, the low-temperature fuel cell stack is not started up; Fuel cell system.

3. The controller includes: When the first pressure is lower than the first pressure lower limit, the fuel gas in the high-temperature fuel cell stack is diluted with air and discharged; When the second pressure is lower than the second pressure lower limit value, the fuel gas in the low-temperature fuel cell stack is diluted with air and discharged. The fuel cell system according to claim 2 .

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