Control device, fuel cell system, and control method

Abstract

A control device (16) of a fuel cell system (12), which has a plurality of fuel cell units (18) and a plurality of pump units (24) capable of supplying scavenging gases to the respective plurality of fuel cell units, comprises: a scavenging processing unit (56) that performs a first scavenging process when power generation by the plurality of fuel cell units is suspended; a determination unit (58) that determines whether or not a prescribed period has elapsed since the first scavenging process was started; and a scavenging prohibition unit (60) that prohibits a second scavenging process at least until the prescribed period has elapsed since the first scavenging process was started.

Description

Control Device, Fuel Cell System, and Control Method

[0001] The present disclosure relates to a control device, a fuel cell system, and a control method.

[0002] In recent years, in order for more people to access affordable, reliable, sustainable, and advanced energy, research and development on fuel cells that contribute to energy efficiency have been conducted. For example, Japanese Unexamined Patent Application Publication No. 2019-145432 discloses a fuel cell system capable of performing scavenging.

[0003] Regarding a fuel cell system capable of performing scavenging, better technologies are desired.

[0004] The present disclosure aims to solve the above-described problems.

[0005] A first aspect of the present disclosure is a control device for a fuel cell system having a plurality of fuel cell units and a plurality of pump units capable of supplying scavenging gas to each of the plurality of fuel cell units, the control device including: a scavenging processing unit that controls a first pump unit, which is a pump unit corresponding to a first fuel cell unit among the plurality of fuel cell units, to perform a first scavenging process, which is a scavenging process for the first fuel cell unit, when the plurality of fuel cell units are in a power generation suspension state; a determination unit that determines whether a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition unit that prohibits a second scavenging process, which is the scavenging process for a second fuel cell unit among the plurality of fuel cell units, until at least the predetermined period has elapsed since the start of the first scavenging process.

[0006] A second aspect of the present disclosure is a fuel cell system including the control device according to the first aspect of the present disclosure, the plurality of fuel cell units, and the plurality of pump units.

[0007] A third aspect of the present disclosure is a control method for a fuel cell system having a plurality of fuel cell units and a plurality of pump units capable of supplying scavenging gas to each of the plurality of fuel cell units, comprising: a first scavenging process start step of controlling a first pump unit which is a pump unit corresponding to a first fuel cell unit among the plurality of fuel cell units when the plurality of fuel cell units are not generating power; a determination step of determining whether a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition step of prohibiting the second scavenging process which is the scavenging process for a second fuel cell unit among the plurality of fuel cell units until at least the predetermined period has elapsed since the start of the first scavenging process.

[0008] According to this disclosure, the noise, vibration, and other sensations caused by the scavenging process that may cause discomfort to users of the fuel cell system are suppressed and mitigated.

[0009] Figure 1 is a diagram illustrating the configuration of a fuel cell system according to one embodiment. Figure 2 is a flowchart of a control method according to one embodiment. Figure 3A is a graph illustrating the time-series change in the rotational speed of the first pump section. Figure 3B is a graph illustrating the time-series change in the rotational speed of the second pump section. Figure 4 is a graph illustrating the time-series change in the NV level generated by the entire fuel cell system.

[0010] In fuel cell technology, it is desirable to minimize any discomfort caused by the scavenging process to the user of the fuel cell system. To minimize this discomfort, Japanese Patent Publication No. 2019-145432 proposes a fuel cell system that performs scavenging on multiple fuel cells simultaneously.

[0011] However, conventional fuel cell systems that perform scavenging on multiple fuel cells simultaneously have the following problem: the noise and vibration (NV) generated when the scavenging process of multiple fuel cells starts at the same time may cause discomfort to the user. For example, the scavenging process involves driving an air pump to supply scavenging gas to the gas flow path connected to the fuel cell. This scavenging gas discharges any water remaining in the gas flow path. In this case, the driven air pump becomes a source of noise or vibration.

[0012] Based on the preliminary explanation above, one embodiment will be described below. In the following description, the term "program" (computer program, computer software) is also referred to as a "computer program product." A computer program product is not limited to programs stored on a storage medium (recording medium), but also includes programs transmitted, distributed, and downloaded via networks such as the Internet.

[0013] (One Embodiment) Figure 1 is a diagram showing the configuration of a fuel cell system 12 according to one embodiment.

[0014] The fuel cell system 12 is installed in a vehicle 10, such as a fuel cell vehicle. The fuel cell system 12 has a plurality of power generation systems 14 and a control device 16.

[0015] Each of the multiple power generation systems 14 includes a fuel cell unit 18, a cathode gas supply device 20, and an anode gas supply device 22.

[0016] The fuel cell unit 18 has a fuel cell. The fuel cell unit 18 may have multiple fuel cells. For example, the fuel cell unit 18 may be a fuel cell stack. Although not shown in the figures, the fuel cell unit 18 has a cathode (cathode electrode), an anode (anode electrode), and an electrolyte membrane disposed between the cathode and the anode. The electrolyte membrane is, for example, a solid polymer electrolyte membrane.

[0017] The cathode gas supply device 20 comprises a pump unit 24, a cathode gas flow path 26, a cathode off-gas flow path 28, and a humidifier 30.

[0018] The pump unit 24 includes a device that supplies an oxygen-containing cathode gas to the cathode gas flow path 26. For example, an air pump is included in the pump unit 24. The cathode gas is, for example, air.

[0019] The cathode gas flow path 26 connects the pump unit 24 to the fuel cell unit 18 (the cathode of the fuel cell unit 18). This allows the pump unit 24 to supply cathode gas to the cathode.

[0020] The cathode-off gas channel 28 connects the fuel cell unit 18 (the cathode of the fuel cell unit 18) to a dilution box (not shown). The cathode-off gas discharged from the cathode is exhausted into the dilution box via the cathode-off gas channel 28.

[0021] The humidifier 30 is connected to the cathode gas flow path 26 and the cathode off gas flow path 28. The humidifier 30 exchanges moisture and heat between the cathode gas flowing through the cathode gas flow path 26 and the cathode off gas flowing through the cathode off gas flow path 28.

[0022] The anode gas supply device 22 includes an anode gas flow path 32, an anode off-gas flow path 34, an anode gas circulation path 36, an ejector 38, a shut-off valve 40, and a purge valve 42.

[0023] The anode gas flow path 32 connects an anode (anode electrode) (not shown) provided in the fuel cell unit 18 to a fuel tank (not shown). The fuel tank stores anode gas, which is fuel gas. The anode gas is, for example, hydrogen gas. The anode gas is supplied from the fuel tank to the anode via the anode gas flow path 32.

[0024] The anode off-gas flow path 34 connects the fuel cell unit 18 (the anode of the fuel cell unit 18) to a dilution box (not shown, as described above). The anode off-gas discharged from the anode may be exhausted into the dilution box via the anode off-gas flow path 34.

[0025] The anode gas circulation path 36 connects the anode gas flow path 32 and the anode off-gas flow path 34. Unused anode gas may flow from the anode into the anode off-gas flow path 34. Unused anode gas is anode gas that was supplied to the anode via the anode gas flow path 32 but was not consumed by the anode. This unused anode gas can flow from the anode off-gas flow path 34 into the anode gas flow path 32 via the anode gas circulation path 36.

[0026] The ejector 38 is provided in the anode gas flow path 32. The ejector 38 is located between the fuel cell unit 18 and the shut-off valve 40, which will be described later. The ejector 38 causes the anode gas to flow from the fuel tank towards the fuel cell unit 18. The ejector 38 also draws in unused anode gas from the anode off-gas flow path 34. As shown in Figure 1, the ejector 38 may be located at the connection point between the anode gas flow path 32 and the anode gas circulation path 36.

[0027] The shut-off valve 40 is provided in the anode gas passage 32. The shut-off valve 40 is located between the ejector 38 and the fuel tank. When the shut-off valve 40 is closed, the amount of anode gas supplied from the fuel tank to the fuel cell unit 18 is reduced compared to when the shut-off valve 40 is open.

[0028] The purge valve 42 is provided in the anode off-gas flow path 34. The purge valve 42 is located between the branch 44 of the anode off-gas flow path 34 to the anode gas circulation path 36 and the aforementioned dilution box (not shown). When the purge valve 42 is closed, the amount of anode off-gas exhausted into the dilution box is reduced compared to when the purge valve 42 is open.

[0029] The power generation system 14 is further equipped with a temperature sensor 48. The temperature sensor 48 is a sensor for detecting the temperature of the fuel cell unit 18. Each of the multiple power generation systems 14 is equipped with a temperature sensor 48.

[0030] Although not shown in the diagram, the fuel cell unit 18 is connected to a refrigerant circuit. The refrigerant circuit is a fluid circuit that circulates refrigerant between the fuel cell unit 18 and a cooler (not shown). The cooler includes a device for cooling the refrigerant. For example, a radiator capable of cooling the refrigerant is included in the cooler. The refrigerant is supplied, for example, between multiple unit cells formed in the fuel cell stack described above. There is a correlation (causal relationship) between the temperature change of the fuel cell unit 18 and the temperature change of the refrigerant from which heat is recovered from the fuel cell unit 18. Based on this, the temperature sensor 48 may detect the temperature of the refrigerant in the refrigerant circuit. The detection signal output from the temperature sensor 48 according to the temperature of the refrigerant from which heat is recovered from the fuel cell unit 18 is substantially a detection signal according to the temperature of the fuel cell unit 18.

[0031] The control device 16 is an electronic device that controls the scavenging process of the fuel cell unit 18. For example, a computer such as an ECU (Electronic Control Unit) is included in the control device 16. As described above, each of the multiple power generation systems 14 is equipped with a fuel cell unit 18. Therefore, the entire fuel cell system 12 has multiple fuel cell units 18. The control device 16 controls the scavenging process of these multiple fuel cell units 18.

[0032] As shown in Figure 1, the control device 16 includes a storage unit 50 and an arithmetic unit 52.

[0033] The storage unit 50 includes one or more memories. The storage unit 50 includes non-volatile memory such as ROM (Read Only Memory), flash memory, or magnetic disk. Non-volatile memory is a storage medium that stores programs, tables, maps, etc., on a non-temporary basis. At least a part of the storage unit 50 may be implemented by a storage medium such as USB (Universal Serial Bus) memory, memory card, or optical disk. The storage unit 50 may also include volatile memory such as RAM (Random Access Memory).

[0034] The arithmetic unit 52 includes a processing circuit capable of performing arithmetic processing. This processing circuit may have one or more processors. For example, the processing circuit may have a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc. The processing circuit may have an IC (Integrated Circuit) or discrete devices.

[0035] The arithmetic unit 52 includes a temperature acquisition unit 54, a scavenging processing unit 56, a determination unit 58, and a scavenging prohibition unit 60. The temperature acquisition unit 54, the scavenging processing unit 56, the determination unit 58, and the scavenging prohibition unit 60 are realized by the processing circuit described above. For example, the temperature acquisition unit 54, the scavenging processing unit 56, the determination unit 58, and the scavenging prohibition unit 60 are realized by the execution of a program stored in the storage unit 50 by the processor of the arithmetic unit 52. At least one of the above-mentioned IC and discrete device may realize at least a part of the temperature acquisition unit 54, the scavenging processing unit 56, the determination unit 58, and the scavenging prohibition unit 60.

[0036] The temperature acquisition unit 54 acquires temperature information. The temperature information is information indicating the temperature of each of the multiple fuel cell units 18 provided in the fuel cell system 12. The temperature acquisition unit 54 can acquire temperature information based on detection signals from multiple temperature sensors 48 provided in each of the multiple power generation systems 14.

[0037] The scavenging unit 56 controls a plurality of pump units 24 corresponding to each of the plurality of fuel cell units 18 to perform scavenging for each of the plurality of fuel cell units 18. The scavenging process includes the scavenging gas supply process described below. The scavenging process may also further include the moisture adjustment process and the oxygen concentration adjustment process described below (see also Figures 3A and 3B).

[0038] In the scavenging gas supply process, the scavenging unit 56 drives the pump unit 24 at a relatively high rotational speed. This supplies scavenging gas to the cathode of the fuel cell unit 18 via the cathode gas flow path 26. The scavenging gas is, for example, air. Due to fuel crossover, hydrogen may move from the anode to the cathode via the electrolyte membrane. In the scavenging gas supply process, the hydrogen that has moved from the anode to the cathode is discharged into the cathode-off gas flow path 28 along with the scavenging gas.

[0039] The moisture adjustment process is performed after the scavenging gas supply process. In the moisture adjustment process, the scavenging unit 56 reduces the rotational speed of the pump unit 24 compared to the scavenging gas supply process, and also causes the fuel cell unit 18 to generate electricity. The fuel cell unit 18 heats up by generating electricity. As a result, the moisture content in the fuel cell unit 18 is reduced. More specifically, the moisture content of the electrolyte membrane provided in the fuel cell unit 18 is reduced. The amount of electricity generated by the fuel cell unit 18 during the moisture adjustment process is kept relatively low.

[0040] The oxygen concentration adjustment process is performed after the moisture adjustment process. In the oxygen concentration adjustment process, the scavenging unit 56 further reduces the rotation speed of the pump unit 24 compared to the moisture adjustment process, and supplies hydrogen to the anode of the fuel cell unit 18. As a result, the oxygen remaining in the cathode is consumed by a chemical reaction with the hydrogen. Consequently, the oxygen concentration in the cathode is adjusted. More specifically, the oxygen concentration in the cathode is reduced. By reducing the oxygen concentration in the cathode, oxidation of the components of the fuel cell unit 18 (cathode) is suppressed. In addition, as the oxygen concentration in the cathode decreases, for example, the nitrogen concentration in the cathode increases.

[0041] The scavenging unit 56 may decide whether or not to perform scavenging on the multiple fuel cell units 18 based on whether or not predetermined processing start conditions are met. In this case, for example, if the multiple fuel cell units 18 have stopped generating power and the temperature of at least one of the multiple fuel cell units 18 is below a predetermined temperature threshold, the scavenging unit 56 may determine that the predetermined processing start conditions have been met. The scavenging unit 56 can determine whether or not the temperature of at least one of the multiple fuel cell units 18 is below a predetermined temperature threshold based on the temperature of the fuel cell units 18 obtained by the temperature acquisition unit 54. The predetermined temperature threshold is determined, for example, based on experiments, simulations, etc., conducted in advance.

[0042] When the predetermined processing start conditions are met, the scavenging processing unit 56 starts the fuel cell system 12, which is in a power generation shutdown state, and executes the first fuel cell unit identification process. In this case, the fuel cell system 12 may be started using the Real Time Clock (RTC).

[0043] The first fuel cell unit identification process is a process to identify the first fuel cell unit 181 from among a plurality of fuel cell units 18. The first fuel cell unit identification process includes a process in which the scavenging processing unit 56 compares the temperatures of the plurality of fuel cell units 18 based on the results obtained by the temperature acquisition unit 54. As a result, the scavenging processing unit 56 identifies the fuel cell unit 18 with the lowest temperature among the plurality of fuel cell units 18 as the first fuel cell unit 181.

[0044] When the first fuel cell unit 181 is specified, the scavenging unit 56 executes the first scavenging process. The first scavenging process is a scavenging process for the first fuel cell unit 181. The first scavenging process includes, for example, a scavenging gas supply process executed for the first fuel cell unit 181, a moisture adjustment process executed for the first fuel cell unit 181, and an oxygen concentration adjustment process executed for the first fuel cell unit 181. The scavenging unit 56 controls the first pump unit 241 to execute the first scavenging process. The first pump unit 241 is the pump unit 24 corresponding to the first fuel cell unit 181. That is, the first pump unit 241 is the pump unit 24 that supplies scavenging gas to the first fuel cell unit 181.

[0045] The determination unit 58 determines whether or not a predetermined period has elapsed since the start of the first scavenging process. It is preferable that the predetermined period includes the execution period of the scavenging gas supply process of the first scavenging process. The predetermined period may further include the execution period of the moisture adjustment process of the first scavenging process. The predetermined period may further include the execution period of the oxygen concentration adjustment process of the first scavenging process.

[0046] The predetermined period may be a period during which the first pump unit 241 is driven so that the rotation speed of the first pump unit 241 becomes equal to or higher than a predetermined rotation speed threshold. The rotation speed threshold is determined based on, for example, experiments, simulations, etc. performed in advance.

[0047] The rotation speed threshold may be set to be lower than the rotation speed of the first pump unit 241 in the scavenging gas supply process of the first scavenging process. Thereby, the execution period of the scavenging gas supply process of the first scavenging process is substantially included in the predetermined period.

[0048] Also, the rotation speed threshold may be set to be lower than the rotation speed of the first pump unit 241 in the moisture adjustment process of the first scavenging process. Thereby, the execution periods of the scavenging gas supply process and the moisture adjustment process of the first scavenging process are substantially included in the predetermined period.

[0049] Furthermore, the rotational speed threshold may be set lower than the rotational speed of the first pump unit 241 in the oxygen concentration adjustment process of the first scavenging process. This ensures that the execution periods of the scavenging gas supply process, the moisture adjustment process, and the oxygen concentration adjustment process of the first scavenging process are substantially encompassed within a predetermined period.

[0050] The scavenging prohibition unit 60 prohibits the second scavenging process from the start of the first scavenging process until a predetermined period of time has elapsed at the earliest. The second scavenging process is a scavenging process for the second fuel cell unit 182. The second fuel cell unit 182 is a fuel cell unit 18 other than the first fuel cell unit 181 among the plurality of fuel cell units 18. The scavenging prohibition unit 60 determines whether a predetermined period of time has elapsed since the start of the first scavenging process based on the result of the determination by the determination unit 58.

[0051] If the second scavenging process is prohibited by the scavenging prohibition unit 60, the scavenging processing unit 56 described above will not perform the second scavenging process. The scavenging prohibition unit 60 will permit the second scavenging process at the earliest after a predetermined period has elapsed. As a result, the scavenging processing unit 56 described above will perform the second scavenging process at the earliest after a predetermined period has elapsed. Therefore, according to this embodiment, there is a time difference of at least a predetermined period between the start timing of the first scavenging process and the start timing of the second scavenging process.

[0052] Figure 2 is a flowchart of a control method according to one embodiment.

[0053] The control device 16 (computer) can execute the scavenging control method shown in Figure 2 based on the program. As shown in Figure 2, the scavenging control method includes a temperature acquisition step S1, a condition determination step S2, a first scavenging process start step S3, a scavenging prohibition step S4, a determination step S5, a scavenging permission step S6, and a second scavenging process start step S7.

[0054] In the temperature acquisition step S1, the temperature acquisition unit 54 acquires the temperature of each of the multiple fuel cell units 18. In the condition determination step S2, the scavenging unit 56 determines whether or not predetermined processing start conditions are met.

[0055] If the predetermined processing start conditions are not met, the scavenging control method terminates. If the predetermined processing start conditions are met, the first scavenging process start step S3 is started.

[0056] In the first scavenging process initiation step S3, the scavenging processing unit 56 starts the first scavenging process. The first fuel cell unit 181, which is the target of the first scavenging process, may be identified based on the results obtained in the temperature acquisition step S1.

[0057] In the scavenging prohibition step S4, the scavenging prohibition unit 60 prohibits the second scavenging process. In the determination step S5, the determination unit 58 determines whether a predetermined period of time has elapsed since the start of the first scavenging process.

[0058] If a predetermined period has not elapsed since the start of the first scavenging process, the determination step S5 is repeated. If a predetermined period has elapsed since the start of the first scavenging process, the scavenging permission step S6 is started.

[0059] In the scavenging permission step S6, the scavenging prohibition unit 60 authorizes the second scavenging process. This triggers the execution of the second scavenging process start step S7. In the second scavenging process start step S7, the scavenging processing unit 56 starts the second scavenging process.

[0060] Figure 3A is a graph illustrating the time-series change in the rotational speed of the first pump unit 241. Figure 3B is a graph illustrating the time-series change in the rotational speed of the second pump unit 242. The second pump unit 242 is the same pump unit 24 used for the second scavenging process.

[0061] Figure 3A shows the first time point t1, the second time point t2, the third time point t3, and the fourth time point t4. The first scavenging process is performed during the period from the first time point t1 to the fourth time point t4. The scavenging gas supply process of the first scavenging process is performed during the period from the first time point t1 to the second time point t2. The moisture adjustment process of the first scavenging process is performed during the period from the second time point t2 to the third time point t3. The oxygen concentration adjustment process of the first scavenging process is performed during the period from the third time point t3 to the fourth time point t4.

[0062] The higher the rotational speed of the pump unit 24, the greater the NV (Noise Variability) generated by the scavenging process performed by driving the pump unit 24. If multiple pump units 24 are driven simultaneously at relatively high rotational speeds for the scavenging process, there is a risk that the fuel cell system 12 as a whole will generate relatively high NV. Furthermore, this relatively high NV may cause discomfort to the user of the fuel cell system 12 (vehicle 10).

[0063] In this respect, according to this embodiment, the control device 16 is equipped with a scavenging prohibition unit 60. The scavenging prohibition unit 60 prohibits the second scavenging process until at least a predetermined period has elapsed after the start of the first scavenging process. As a result, as shown by comparing Figure 3A and Figure 3B, the predetermined period during which the first pump unit 241 is driven at a relatively high rotational speed does not overlap with the execution period of the second scavenging process. In the example of Figures 3A and 3B, the predetermined period includes the first time point t1 to the second time point t2. The second scavenging process is performed during the period from the second time point t2 to the fifth time point t5 in Figure 3B. The required time for the scavenging gas supply process, the required time for the moisture adjustment process, and the required time for the oxygen concentration adjustment process are conveniently unified in the example of Figures 3A and 3B, but they may be different.

[0064] Figure 4 is a graph illustrating the time-series change in NV level generated by the entire fuel cell system 12. The NV level (vertical axis) indicates the magnitude of the NV mentioned above. The unit of the NV level is, for example, decibels.

[0065] Multiple NV levels (NVA to NVC, NVx) are shown in Figure 4.

[0066] NVA is the NV level generated by the pump unit 24 during the scavenging gas supply process. In the example shown in Figure 4, the maximum value of the NV level during the period from the first time point t1 to the second time point t2 reaches NVA. The period from the first time point t1 to the second time point t2 is the period (predetermined period) during which the scavenging gas supply process of the first scavenging process is performed.

[0067] NVB is the sum of NVb1 and NVb2 (NVB = NVb1 + NVb2). NVb1 is the level of NV generated by the first pump unit 241 during the moisture adjustment process of the first scavenging process (after a predetermined period of time). NVb2 is the level of NV generated by the second pump unit 242 during the scavenging gas supply process of the second scavenging process, which is started after a predetermined period of time. In the example in Figure 4, the maximum value of the NV level during the period from the second time point t2 to the third time point t3 reaches NVB.

[0068] NVb2 and NVA are both NV values ​​in the scavenging gas supply process. Based on this, NVb2 and NVA shown in Figure 4 are approximately the same (NVb2 ≈ NVA). Also, as mentioned above, the rotational speed of the pump unit 24 in the moisture adjustment process is smaller than the rotational speed of the pump unit 24 in the scavenging gas supply process. Therefore, NVb1 is smaller than both NVA and NVB (NVb1 < NVA; NVb1 < NVB).

[0069] NVC is the sum of NVc1 and NVc2 (NVC = NVc1 + NVc2). NVc1 is the level of NV generated by the first pump unit 241 during the oxygen concentration adjustment process of the first scavenging process. NVc2 is the level of NV generated by the second pump unit 242 during the moisture adjustment process of the second scavenging process. In the example in Figure 4, the maximum value of the NV level during the period from the third time point t3 to the fourth time point t4 reaches NVC.

[0070] NVb1 and NVc2 are both NV values ​​in the moisture adjustment process. Based on this, NVb1 and NVc2 shown in Figure 4 are approximately the same (NVb1 ≈ NVc2). Also, as mentioned above, the rotational speed of the pump unit 24 in the oxygen concentration adjustment process is smaller than the rotational speed of the pump unit 24 in the moisture adjustment process. Therefore, NVc1 is smaller than both NVb1 and NVc2 (NVc1 < NVb1; NVc1 < NVc2).

[0071] NVx is shown for comparison with NVA to NVC. NVx is the NV level when the scavenging gas supply process of the first scavenging process and the scavenging gas supply process of the second scavenging process are started simultaneously. NVx corresponds to the sum of NVA and NVb2 (NVx = NVA + NVb2). For example, if the scavenging gas supply process of the first scavenging process and the scavenging gas supply process of the second scavenging process are started simultaneously, the maximum value of the NV level during the period from the first time point t1 to the second time point t2 reaches NVx (see also the dashed line in Figure 4).

[0072] As shown in Figure 4, according to this embodiment, NVA to NVC can be kept smaller than NVx. In other words, according to this embodiment, the control device 16 can suppress the maximum value of the NV level generated from the fuel cell system 12 by the scavenging process. As a result, the control device 16 can suppress and mitigate the discomfort that the NV generated by the scavenging process causes to the user of the fuel cell system 12.

[0073] As described above, the predetermined period includes the execution period of the scavenging gas supply process of the first scavenging process, but may also include the execution period of the moisture adjustment process of the first scavenging process. In this case as well, the predetermined period during which the first pump unit 241 is driven at a relatively high rotational speed does not overlap with the execution period of the second scavenging process. Therefore, the control device 16 can suppress and mitigate any discomfort caused by the NV generated by the scavenging process to the user of the fuel cell system 12. In this case, the scavenging gas supply process of the second scavenging process and the oxygen concentration adjustment process of the first scavenging process may be executed in parallel. The rotational speed of the first pump unit 241 in the oxygen concentration adjustment process of the first scavenging process is smaller than the rotational speed of the first pump unit 241 in the moisture adjustment process of the first scavenging process. Therefore, the NV level generated when the scavenging gas supply process of the second scavenging process and the oxygen concentration adjustment process of the first scavenging process are performed in parallel is smaller than the NV level generated when the scavenging gas supply process of the second scavenging process and the moisture adjustment process of the first scavenging process are performed in parallel. In other words, the control device 16 can further suppress the maximum value (maximum value) of the NV level generated from the fuel cell system 12 by the scavenging process. As a result, the control device 16 can further suppress and mitigate the discomfort that the NV generated by the scavenging process causes to the user of the fuel cell system 12.

[0074] As described above, the predetermined period may further include the execution period for the oxygen concentration adjustment treatment of the first scavenging treatment. In this case as well, the predetermined period during which the first pump unit 241 is driven at a relatively high rotational speed and the execution period for the second scavenging treatment do not overlap. Moreover, in this case, the second scavenging treatment is performed after the first scavenging treatment is completed. Therefore, the NV generated by the first pump unit 241 during the first scavenging treatment and the NV generated by the second pump unit 242 during the second scavenging treatment do not overlap. In other words, the maximum value of the NV level generated from the fuel cell system 12 by the scavenging treatment is further suppressed.

[0075] The control device 16 includes a temperature acquisition unit 54. When multiple fuel cell units 18 are shut down and the temperature of at least one of the multiple fuel cell units 18 is below a predetermined temperature, the scavenging unit 56 may perform a plurality of scavenging processes, including a first scavenging process. When the temperature of the fuel cell unit 18 is relatively low, the risk of moisture freezing inside the fuel cell unit 18 (cathode gas flow path) increases. The control device 16 can suppress the occurrence of moisture freezing by performing a scavenging process when the temperature of at least one of the multiple fuel cell units 18 is below a predetermined temperature.

[0076] The scavenging unit 56 preferably identifies the fuel cell unit 18 with the lowest temperature among the multiple fuel cell units 18 as the first fuel cell unit 181. The fuel cell unit 18 with the lowest temperature among the multiple fuel cell units 18 is the fuel cell unit 18 with the highest risk of moisture freezing occurring. The control device 16 (scavenging unit 56) can preferentially perform the scavenging process on the fuel cell unit 18 with the highest risk of moisture freezing as the first scavenging process.

[0077] The predetermined period may be the period during which the first pump unit 241 is driven so that its rotational speed is equal to or greater than a predetermined rotational speed threshold. In this case as well, the predetermined period during which the first pump unit 241 is driven at a relatively high rotational speed and the execution period of the second scavenging process do not overlap. Therefore, the control device 16 can further suppress and mitigate the discomfort that NV generated by the scavenging process causes to the user of the fuel cell system 12.

[0078] One embodiment may be modified as follows. In the following modifications, explanations that overlap with the embodiment will be omitted as appropriate. Also, in the figures used in the following modifications, components identical to those described in the embodiment will be denoted by the same reference numerals.

[0079] (Modification 1) The number of power generation systems 14 provided in the fuel cell system 12 is not limited to two (Figure 1). Three or more power generation systems 14 may be provided in the fuel cell system 12. In this case, the control device 16 will make the start timing of the scavenging process different for at least two of the three or more fuel cell units 18. This allows the control device 16 to suppress and mitigate any discomfort caused to the user of the fuel cell system 12 by the NV generated by the scavenging process.

[0080] The control device 16 may set different start timings for the scavenging process for each of the three or more fuel cell units 18. This allows the control device 16 to further suppress and mitigate any discomfort caused by NV generated by the scavenging process to the user of the fuel cell system 12.

[0081] (Modification 2) Multiple electronic devices (computers) that can communicate with each other may be provided as substantially a single control device 16. For example, multiple ECUs provided in a vehicle 10 may realize substantially a single control device 16.

[0082] (Combinations of multiple variations) The above-mentioned variations may be combined as appropriate, within the bounds of consistency.

[0083] With regard to the embodiments described above, the following additional information is disclosed.

[0084] (Note 1) The control device (16) according to the present disclosure is a control device for a fuel cell system (12) having a plurality of fuel cell units (18) and a plurality of pump units (24) capable of supplying scavenging gas to each of the plurality of fuel cell units, and comprises: a scavenging processing unit (56) that controls a first pump unit (241) which is a pump unit corresponding to a first fuel cell unit (181) among the plurality of fuel cell units when the plurality of fuel cell units are not generating power, to execute a first scavenging process which is a scavenging process for the first fuel cell unit; a determination unit (58) that determines whether a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition unit (60) that prohibits the second scavenging process which is a scavenging process for a second fuel cell unit (182) among the plurality of fuel cell units until at least the predetermined period has elapsed since the start of the first scavenging process. As a result, the control device can suppress and mitigate the discomfort caused by NV generated by the scavenging process to the user of the fuel cell system.

[0085] (Note 2) The control device described in Note 1, wherein the first scavenging process includes a scavenging gas supply process in which the scavenging gas is supplied to the cathode of the first fuel cell unit, and the predetermined period may include the execution period of the scavenging gas supply process.

[0086] (Note 3) The control device described in Note 2, wherein the first scavenging treatment further includes a moisture adjustment treatment that reduces the moisture contained in the first fuel cell by generating electricity after the scavenging gas supply treatment, and the predetermined period further includes the period for performing the moisture adjustment treatment.

[0087] (Note 4) The control device described in Note 3, wherein the first scavenging treatment further includes an oxygen concentration adjustment treatment that adjusts the oxygen concentration of the cathode by reacting the oxygen remaining in the cathode with hydrogen after the moisture adjustment treatment, and the predetermined period further includes the period for performing the oxygen concentration adjustment treatment.

[0088] (Note 5) In the control device described in any one of Notes 1 to 4, the scavenging unit may start the first scavenging process when the plurality of fuel cell units have stopped generating power and the temperature of at least one of the plurality of fuel cell units is below a predetermined temperature threshold. This allows the control device to suppress the occurrence of moisture freezing inside the fuel cell unit.

[0089] (Note 6) In the control device described in Note 5, the scavenging unit may identify the fuel cell unit with the lowest temperature among the plurality of fuel cell units as the first fuel cell unit. This allows the control device to preferentially perform scavenging on the fuel cell unit with the highest risk of moisture freezing as the first scavenging process.

[0090] (Note 7) The control device described in any one of Notes 1 to 6, wherein the predetermined period is the period during which the first pump unit is driven so that the rotational speed of the first pump unit is equal to or greater than a predetermined rotational speed threshold. This allows the control device to further suppress and mitigate the discomfort caused to the user of the fuel cell system by the NV generated by the scavenging process.

[0091] (Note 8) The fuel cell system (12) relating to this disclosure comprises a control device described in any one of Notes 1 to 7, the plurality of fuel cell units, and the plurality of pump units.

[0092] (Note 9) The control method according to the present disclosure is a control method for a fuel cell system (12) having a plurality of fuel cell units (18) and a plurality of pump units (24) capable of supplying scavenging gas to each of the plurality of fuel cell units, comprising: a first scavenging process start step (S3) in which, when the plurality of fuel cell units are not generating power, a first pump unit (241) which is a pump unit corresponding to a first fuel cell unit (181) among the plurality of fuel cell units is controlled to start a first scavenging process which is a scavenging process for the first fuel cell unit; a determination step (S5) in which a determination is made whether or not a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition step (S4) in which a second scavenging process which is a scavenging process for a second fuel cell unit (182) among the plurality of fuel cell units is prohibited until at least the predetermined period has elapsed since the start of the first scavenging process.

[0093] Furthermore, the present invention may take various configurations without departing from the gist of this disclosure, and is not limited to the disclosure described above.

[0094] 12...Fuel cell system 16...Control device 18...Fuel cell unit 24...Pump unit 56...Scavenging processing unit 58...Determination unit 60...Scavenging prohibition unit 181...First fuel cell unit 182...Second fuel cell unit 241...First pump unit

Claims

1. A control device (16) for a fuel cell system (12) having a plurality of fuel cell units (18) and a plurality of pump units (24) capable of supplying scavenging gas to each of the plurality of fuel cell units, comprising: a scavenging processing unit (56) that controls a first pump unit (241) which corresponds to a first fuel cell unit (181) among the plurality of fuel cell units when the plurality of fuel cell units are not generating power, to perform a first scavenging process which is a scavenging process for the first fuel cell unit; a determination unit (58) that determines whether a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition unit (60) that prohibits the second scavenging process which is a scavenging process for a second fuel cell unit (182) among the plurality of fuel cell units until at least the predetermined period has elapsed since the start of the first scavenging process.

2. A control device according to claim 1, wherein the first scavenging process includes a scavenging gas supply process in which the scavenging gas is supplied to the cathode of the first fuel cell unit, and the predetermined period includes the execution period of the scavenging gas supply process.

3. A control device according to claim 2, wherein the first scavenging process further includes a moisture adjustment process that reduces the moisture contained in the first fuel cell by generating electricity after the scavenging gas supply process, and the predetermined period further includes a period for performing the moisture adjustment process.

4. A control device according to claim 3, wherein the first scavenging treatment further includes an oxygen concentration adjustment treatment that adjusts the oxygen concentration of the cathode by reacting the oxygen remaining in the cathode with hydrogen after the moisture adjustment treatment, and the predetermined period further includes a period for performing the oxygen concentration adjustment treatment.

5. A control device according to any one of claims 1 to 4, wherein the scavenging unit starts the first scavenging process when the plurality of fuel cell units stop generating power and the temperature of at least one of the plurality of fuel cell units is below a predetermined temperature threshold.

6. A control device according to claim 5, wherein the scavenging unit identifies the fuel cell unit with the lowest temperature among the plurality of fuel cell units as the first fuel cell unit.

7. A control device according to any one of claims 1 to 4, wherein the predetermined period is a period during which the first pump unit is driven so that the rotational speed of the first pump unit is equal to or greater than a predetermined rotational speed threshold.

8. A fuel cell system comprising: a control device according to any one of claims 1 to 4; the plurality of fuel cell units; and the plurality of pump units.

9. A control method for a fuel cell system (12) having a plurality of fuel cell units (18) and a plurality of pump units (24) capable of supplying scavenging gas to each of the plurality of fuel cell units, comprising: a first scavenging process start step (S3) in which, when the plurality of fuel cell units are not generating power, a first pump unit (241) which is a pump unit corresponding to a first fuel cell unit (181) among the plurality of fuel cell units is controlled to start a first scavenging process which is a scavenging process for the first fuel cell unit; a determination step (S5) in which a predetermined period has elapsed since the start of the first scavenging process; and a scavenging prohibition step (S4) in which a second scavenging process which is a scavenging process for a second fuel cell unit (182) among the plurality of fuel cell units is prohibited until at least the predetermined period has elapsed since the start of the first scavenging process.

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