Fuel cell system

Abstract

To provide a fuel cell system capable of suppressing deterioration of circulation efficiency of fuel off-gas of an ejector even when upstream pressure of the ejector is low.SOLUTION: The fuel cell system 1 includes the upstream pressure sensor P1 configured to measure the pressure of the hydrogen gas upstream of the ejectors 64, the downstream pressure sensor P2 configured to measure the pressure of the mixture gas of the hydrogen gas and the hydrogen off-gas downstream of the ejectors 64, and the control unit 12 configured to control the injector 63, and the control unit 12 performs the first control of controlling the injector 63 such that the measurement value of the downstream pressure sensor P2 becomes the first target downstream pressure calculated by multiplying the measurement value of the upstream pressure sensor P1 by 0.528.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity when supplied with a fuel gas and an oxidant gas. [Background technology]

[0002] Patent Document 1 discloses a fuel cell system having a fuel cell that receives a supply of fuel gas from a fuel gas system and a supply of oxidant gas from an oxidant gas system to generate electricity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-185247 Summary of the Invention [Problem to be solved by the invention]

[0004] In a fuel cell system, fuel off-gas discharged from a fuel cell is circulated to the fuel cell by an ejector. However, in an operating environment where the upstream pressure of the ejector is low, a sufficient pressure difference cannot be secured between the upstream and downstream of the ejector, and the efficiency of circulating the fuel off-gas through the ejector may decrease.

[0005] Here, in order to prevent a decrease in the circulation efficiency of the fuel off-gas when the upstream pressure is low, it is conceivable to circulate the fuel off-gas to the fuel cell using a pump (i.e., a gas circulation pump) instead of an ejector, as in the fuel cell system disclosed in Patent Document 1. However, pumps are expensive, which increases the manufacturing cost of the fuel cell system, and the addition of a pump could increase the size of the fuel cell system.

[0006] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that can suppress a decrease in the circulation efficiency of the fuel off-gas of the ejector even when the upstream pressure of the ejector is low. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, one aspect of the present disclosure provides a fuel cell system having a fuel cell, a fuel gas supply passage that supplies fuel gas to the fuel cell, a fuel off-gas discharge passage that discharges fuel off-gas discharged from the fuel cell to the outside, a fuel off-gas circulation passage that circulates at least a portion of the fuel off-gas from the fuel off-gas discharge passage to the fuel gas supply passage, a fuel supply device that is disposed in the fuel gas supply passage and supplies the fuel gas, and an ejector that is disposed downstream of the fuel supply device in the fuel gas supply passage and mixes and discharges the fuel gas supplied by the fuel supply device and the fuel off-gas circulated by the fuel off-gas circulation passage, the fuel cell system further comprising: a first pressure sensor that measures a pressure upstream of the ejector; a second pressure sensor that measures a pressure downstream of the ejector; and a control unit that controls the fuel supply device, wherein the control unit performs first control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a first target pressure value calculated by multiplying the measurement value of the first pressure sensor by a value equal to or less than a critical pressure ratio.

[0008] According to this aspect, a sufficient pressure difference between the upstream and downstream of the ejector can be ensured, allowing the fuel gas to flow at the sonic speed within the ejector, thereby preventing a decrease in the circulation efficiency of the fuel off-gas in the ejector even when the upstream pressure of the ejector is low.

[0009] In the above aspect, it is preferable that an atmospheric pressure sensor for measuring atmospheric pressure is provided, and the first target pressure value is set to be equal to or higher than the atmospheric pressure measured by the atmospheric pressure sensor.

[0010] According to this aspect, the downstream pressure of the ejector does not fall below atmospheric pressure, which prevents the catalyst of the fuel cell from being deteriorated by air (i.e., oxygen) drawn into the fuel cell when the downstream pressure of the ejector falls below atmospheric pressure.

[0011] In the above aspect, it is preferable that the control unit performs second control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value higher than the first target pressure value, and repeatedly performs a process of performing the first control for a first predetermined time and a process of performing the second control for a second predetermined time.

[0012] According to this aspect, even when the upstream pressure of the ejector is low, it is possible to suppress a decrease in the circulation efficiency of the fuel off-gas of the ejector, and it is possible to avoid a shortage of fuel gas (more specifically, a mixture of fuel gas and fuel off-gas) supplied to the fuel cell.

[0013] In the above aspect, it is preferable that the control unit performs second control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value higher than the first target pressure value, alternates between the first control and the second control at predetermined time intervals, and controls the fuel supply device so that the measurement value of the second pressure sensor changes continuously over time within the predetermined time interval.

[0014] According to this aspect, even when the upstream pressure of the ejector is low, it is possible to suppress a decrease in the circulation efficiency of the fuel off-gas of the ejector, and to avoid a shortage of the fuel gas (more specifically, a mixed gas of fuel gas and fuel off-gas) supplied to the fuel cell. Furthermore, when switching between the first control and the second control, fluctuations in the amount of fuel gas supplied to the fuel cell are suppressed, thereby stabilizing the power generation efficiency of the fuel cell.

[0015] In the above aspect, it is preferable that the control unit performs second control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value higher than the first target pressure value until a predetermined time has elapsed since the fuel cell was started.

[0016] According to this aspect, when a fuel cell that has been in a power generation stopped state starts generating power, the fuel gas supply passage downstream of the ejector can efficiently discharge accumulated air and nitrogen and supply fuel gas, thereby improving the power generation efficiency of the fuel cell when it starts up.

[0017] In the above aspect, it is preferable that the fuel off-gas discharge passage has an exhaust drain valve that opens and closes the fuel off-gas discharge passage, and when there is a request to open the exhaust drain valve, the control unit performs second control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value that is higher than the first target pressure value.

[0018] According to this aspect, opening the exhaust / drainage valve causes fuel off-gas to be discharged from the fuel cell to the outside, but fuel gas (more specifically, a mixture of fuel gas and fuel off-gas) can be supplied to the fuel cell to compensate for this discharge, thereby preventing a decrease in the power generation efficiency of the fuel cell when the exhaust / drainage valve is open. [Effects of the Invention]

[0019] According to the fuel cell system of the present disclosure, even when the upstream pressure of the ejector is low, it is possible to prevent a decrease in the circulation efficiency of the fuel off-gas in the ejector. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention; [Figure 2] FIG. 3 is a flowchart showing the content of control performed in the first embodiment. [Figure 3] FIG. 10 is a diagram showing the state of fluid flow in an orifice. [Figure 4] FIG. 10 is a diagram showing the relationship between the pressure ratio between the upstream pressure and the downstream pressure at the orifice and the mass flow rate. [Figure 5]FIG. 10 is a flowchart showing the contents of control performed in the second embodiment. [Figure 6] FIG. 10 is a diagram showing an example of a time chart of measured values ​​of a downstream pressure sensor in the second embodiment. [Figure 7] FIG. 11 is a flowchart showing the contents of control performed in the third embodiment. [Figure 8] FIG. 11 is a diagram showing an example of a time chart of measured values ​​of a downstream pressure sensor in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of a fuel cell system according to the present disclosure will be described. In the following description, "upstream" means upstream of the flow of a fluid (i.e., hydrogen gas, hydrogen off-gas, air, air off-gas, etc.), and "downstream" means downstream of the flow of a fluid.

[0022] (Configuration of fuel cell system) First, the configuration of a fuel cell system 1 of this embodiment will be described. As shown in Fig. 1, the fuel cell system 1 has an FC stack 11. The fuel cell system 1 also has a hydrogen system 21, an air system 22, and a cooling system 23. The FC stack 11 is an example of the "fuel cell" of this disclosure.

[0023] The FC stack 11 generates power by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen gas, and the oxidant gas is air. That is, the FC stack 11 generates power by receiving a supply of hydrogen gas from a hydrogen system 21 and a supply of air from an air system 22. The power generated by the FC stack 11 is then supplied to a battery, motor, or the like (not shown).

[0024] The hydrogen system 21 is provided on the anode side of the FC stack 11. The hydrogen system 21 includes a hydrogen gas supply passage 31, a hydrogen off-gas discharge passage 32, a hydrogen gas filling passage 33, and a hydrogen off-gas circulation passage .

[0025] The hydrogen gas supply passage 31 is an example of a "fuel gas supply passage" in the present disclosure. The hydrogen off-gas discharge passage 32 is an example of a "fuel off-gas discharge passage" in the present disclosure. The hydrogen off-gas circulation passage 34 is an example of a "fuel off-gas circulation passage" in the present disclosure.

[0026] The hydrogen gas supply passage 31 is a passage for supplying hydrogen gas from a hydrogen tank 41 in which hydrogen gas is stored to the FC stack 11. The hydrogen off-gas discharge passage 32 is a passage for discharging hydrogen gas (i.e., hydrogen off-gas) discharged from the FC stack 11 to the outside. Note that the hydrogen off-gas is an example of the "fuel off-gas" in this disclosure.

[0027] The hydrogen gas filling passage 33 is a passage for filling hydrogen gas into the hydrogen tank 41 from the filling port 51. The hydrogen off-gas circulation passage 34 is a passage that connects the hydrogen off-gas discharge passage 32 (more specifically, the gas-liquid separator 71) and the ejector 64, and is a passage for circulating at least a portion of the hydrogen off-gas from the hydrogen off-gas discharge passage 32 to the ejector 64 in the hydrogen gas supply passage 31.

[0028] The hydrogen system 21 also includes a valve 61, a pressure reducing valve 62, an injector 63, and an ejector 64 in the hydrogen gas supply passage 31, in this order from the hydrogen tank 41 side.

[0029] Valve 61 is a valve that switches between supplying and blocking hydrogen gas from hydrogen tank 41 to hydrogen gas supply passage 31. Pressure reducing valve 62 is a pressure regulating valve for reducing the pressure of hydrogen gas. Injector 63 is a device for supplying hydrogen gas guided from hydrogen tank 41 to FC stack 11 (more specifically, for injecting it toward ejector 64). Note that injector 63 is an example of a "fuel supply device" in this disclosure.

[0030] The ejector 64 is disposed at a position downstream of the injector 63 in the hydrogen gas supply passage 31. The ejector 64 utilizes the pressure difference upstream and downstream of the ejector 64 to cause the hydrogen gas injected from the injector 63 to flow and generate negative pressure, thereby circulating the hydrogen off-gas sucked from the hydrogen off-gas circulation passage 34, and mixing the hydrogen gas injected by the injector 63 with the hydrogen off-gas circulated by the hydrogen off-gas circulation passage 34 and discharging the resulting mixture toward the FC stack 11 downstream.

[0031] The hydrogen system 21 also includes, in order from the FC stack 11 side, a gas-liquid separator 71 and an exhaust / drain valve 72 in the hydrogen off-gas discharge passage 32. The gas-liquid separator 71 is a device that separates moisture from the hydrogen off-gas. The exhaust / drain valve 72 is a valve that switches between discharging and blocking the hydrogen off-gas and moisture from the gas-liquid separator 71. In other words, the exhaust / drain valve 72 is a valve that is disposed in the hydrogen off-gas discharge passage 32 and opens and closes the hydrogen off-gas discharge passage 32 to control the discharge of hydrogen off-gas to the outside.

[0032] In this embodiment, an upstream pressure sensor P1 and a downstream pressure sensor P2 are provided in the hydrogen gas supply passage 31. The upstream pressure sensor P1 measures the pressure of hydrogen gas upstream of the ejector 64 (more specifically, upstream of the injector 63). The downstream pressure sensor P2 measures the pressure of hydrogen gas downstream of the ejector 64 (more specifically, the mixed gas of hydrogen gas and hydrogen off-gas). The upstream pressure sensor P1 is an example of the "first pressure sensor" of the present disclosure. The downstream pressure sensor P2 is an example of the "second pressure sensor" of the present disclosure.

[0033] On the other hand, the air system 22 is provided on the cathode side of the FC stack 11. This air system 22 includes an air supply passage 81 and an air off-gas discharge passage 82. The air supply passage 81 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11. The air off-gas discharge passage 82 is a passage for discharging air (i.e., air off-gas) discharged from the FC stack 11.

[0034] The air system 22 also includes an air compressor 91 and a supply-side air valve 92 in the air supply passage 81. The air compressor 91 is a device that supplies air to the FC stack 11. The supply-side air valve 92 is a valve that switches between supplying and cutting off air from the air supply passage 81 to the FC stack 11.

[0035] Furthermore, the air system 22 has a discharge-side air valve 101 disposed in the air-offgas discharge passage 82. The discharge-side air valve 101 is a valve that switches between discharging and blocking the air-offgas from the FC stack 11 to the air-offgas discharge passage 82.

[0036] The cooling system 23 is a system that cools the FC stack 11, and includes a cooling water passage 111 and a cooling fan 112. The cooling water passage 111 is a passage through which cooling water flows. The cooling fan 112 is a device that cools the cooling water flowing through the cooling water passage 111.

[0037] The fuel cell system 1 further includes a control unit 12. The control unit 12 is a device having, for example, an arithmetic processing unit such as a CPU, a storage unit such as a ROM for storing control programs and control data processed by the CPU and a RAM used as various work areas for control processing, and an input / output interface unit. The control unit 12 performs various controls of the fuel cell system 1 according to the control programs stored in the storage unit.

[0038] In this embodiment, the control unit 12 controls various components of the fuel cell system 1, such as the valve 61, the injector 63, the gas-liquid separator 71, the exhaust drain valve 72, the air compressor 91, the supply side air valve 92, the discharge side air valve 101, and the cooling fan 112.

[0039] The control unit 12 also acquires information on the measurement value of the upstream pressure of the ejector 64 (specifically, the upstream pressure of the injector 63) from the upstream pressure sensor P1, and information on the measurement value of the downstream pressure of the ejector 64 from the downstream pressure sensor P2.

[0040] In this embodiment, the fuel cell system 1 also has an atmospheric pressure sensor PA that measures the atmospheric pressure inside the fuel cell system 1. The control unit 12 then obtains information about the measured value of the atmospheric pressure inside the fuel cell system 1 from the atmospheric pressure sensor PA.

[0041] (Fuel cell system operation) In the fuel cell system 1 configured as described above, the hydrogen gas supplied from the hydrogen gas supply passage 31 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as hydrogen off-gas via the hydrogen off-gas discharge passage 32 to the outside of the fuel cell system 1. In addition, the air supplied from the air supply passage 81 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas via the air off-gas discharge passage 82 to the outside of the fuel cell system 1.

[0042] (Measures to be taken when the upstream pressure of the ejector is low) In an operating environment where the pressure upstream of the ejector 64 is low (for example, when the fuel cell system 1 is used as a small generator), it may not be possible to ensure a sufficient pressure difference between the upstream and downstream of the ejector 64, which may result in a decrease in the circulation efficiency of the hydrogen off-gas of the ejector 64 (hereinafter simply referred to as "circulation efficiency of hydrogen off-gas"). Here, it is conceivable to circulate the hydrogen off-gas using a pump (not shown) instead of the ejector 64, but in this case, the pump is expensive, which may increase the manufacturing cost of the fuel cell system 1, and the addition of the pump may increase the size of the fuel cell system 1.

[0043] Therefore, in this embodiment, the hydrogen off-gas is circulated using an inexpensive ejector 64, and measures are taken to prevent a decrease in the circulation efficiency of the hydrogen off-gas even when the upstream pressure of the ejector 64 is low.

[0044] <First Example> First, a description will be given of Example 1. In this example, the control unit 12 performs the control shown in FIG.

[0045] As shown in Figure 2, first, the control unit 12 determines whether a predetermined time (e.g., 10 seconds) has elapsed since the FC stack 11 started up (i.e., since the FC stack 11, which had been in a stopped power generation state, started generating power), or whether there is a request to open the exhaust drain valve 72 (step S1).

[0046] Then, if a predetermined time has elapsed since the start-up of the FC stack 11 and there is no request to open the exhaust drain valve 72 (step S1: NO), the control unit 12 sets the value obtained by multiplying the measurement value of the upstream pressure sensor P1 by 0.528 as the first target downstream pressure, which is the target value for the downstream pressure of the ejector 64 (step S2). However, at this time, the first target downstream pressure is set to be equal to or greater than the measurement value of the atmospheric pressure measured by the atmospheric pressure sensor PA. The first target downstream pressure is an example of the "first target pressure value" in this disclosure.

[0047] In the flow of fluid passing through the orifice OR shown in Fig. 3, when the pressure ratio Pb / Pa is 0.528 (i.e., the critical pressure ratio) or less, the fluid becomes a choked flow and the flow velocity becomes the speed of sound, as shown in Fig. 4. In Figs. 3 and 4, Pa represents the upstream pressure of the orifice OR, Pb represents the downstream pressure of the orifice OR, and Qm represents the mass flow rate.

[0048] Therefore, in this embodiment, the control unit 12 calculates the first target downstream pressure of the ejector 64 by multiplying the measurement value of the upstream pressure sensor P1 by 0.528.

[0049] Then, as shown in FIG. 2, the control unit 12 performs a first control to control the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes the first target downstream pressure (step S3).

[0050] In this way, in this embodiment, the control unit 12 performs a first control to control the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes the first target downstream pressure calculated by multiplying the measurement value of the upstream pressure sensor P1 by 0.528 (i.e., the critical pressure ratio).

[0051] As a result, even when the measurement value of the upstream pressure sensor P1 is low, i.e., when the upstream pressure of the ejector 64 is low, by setting the pressure ratio between the upstream pressure and the downstream pressure of the ejector 64 to 0.528, a sufficient pressure difference is ensured between the upstream and downstream of the ejector 64, and hydrogen gas can flow at the speed of sound within the ejector 64.

[0052] For example, even if the fuel cell system 1 is used as a small generator and the maximum upstream pressure of the ejector 64 is limited to 200 kPaA, by setting the downstream pressure of the ejector 64 to 105.6 kPaA (i.e., 0.528 times the upstream pressure of the ejector 64) and setting the pressure ratio between the upstream pressure and the downstream pressure of the ejector 64 to 0.528, a sufficient pressure difference can be secured between the upstream and downstream of the ejector 64, allowing hydrogen gas to flow at the speed of sound within the ejector 64.

[0053] Therefore, even when the upstream pressure of the ejector 64 is low, negative pressure can be generated by causing the hydrogen gas injected from the injector 63 to flow at the speed of sound. This allows the hydrogen off-gas sucked from the hydrogen off-gas circulation passage 34 to be circulated to the ejector 64, and the hydrogen gas injected by the injector 63 and the hydrogen off-gas circulated by the hydrogen off-gas circulation passage 34 can be mixed and discharged toward the FC stack 11 downstream.

[0054] In this embodiment, the first target downstream pressure is set to be equal to or higher than the atmospheric pressure measured by the atmospheric pressure sensor PA.

[0055] This prevents the downstream pressure of the ejector 64 from falling below atmospheric pressure, thereby preventing the catalyst in the FC stack 11 from deteriorating due to air (i.e., oxygen) being sucked into the FC stack 11 when the downstream pressure of the ejector 64 falls below atmospheric pressure.

[0056] Here, as shown in FIG. 4, not only when the pressure ratio Pb / Pa is 0.528 (i.e., the critical pressure ratio), but also when the pressure ratio Pb / Pa is 0.528 or less, the fluid flow becomes a choked flow and the flow velocity becomes the speed of sound.

[0057] Therefore, in this embodiment, the first target downstream pressure may be a value calculated by multiplying the measurement value of the upstream pressure sensor P1 by a value equal to or less than 0.528. That is, the control unit 12 may perform a first control to control the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes the first target downstream pressure calculated by multiplying the measurement value of the upstream pressure sensor P1 by a value equal to or less than 0.528.

[0058] Returning to the explanation of FIG. 2, in step S1, if a predetermined time has not yet elapsed since the start-up of the FC stack 11 and / or there is a request to open the exhaust drain valve 72 (step S1: YES), the control unit 12 sets a predetermined pressure (e.g., 60 to 80 kPaG) as the second target downstream pressure of the ejector 64 (step S4). The second target downstream pressure is a pressure value higher than the first target downstream pressure, for example, a pressure value 12 to 16 times the first target downstream pressure. The second target downstream pressure is an example of the "second target pressure value" in this disclosure.

[0059] Next, the control unit 12 performs a second control to control the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes the second target downstream pressure (step S3).

[0060] In this way, in this embodiment, a second control is performed to control the FC stack 11 so that the measurement value of the downstream pressure sensor P2 becomes a second target downstream pressure that is higher than the first target downstream pressure until a predetermined time has elapsed since the FC stack 11 was started.

[0061] As a result, when power generation by the FC stack 11 starts, it is possible to efficiently discharge air and nitrogen accumulated in the portion of the hydrogen gas supply passage 31 downstream of the ejector 64, and supply hydrogen gas, thereby improving the power generation efficiency of the FC stack 11 when power generation by the FC stack 11 starts.

[0062] Furthermore, in this embodiment, even when there is a request to open the exhaust drain valve 72, a second control is performed to control the FC stack 11 so that the measurement value of the downstream pressure sensor P2 becomes the second target downstream pressure.

[0063] In this way, by opening the exhaust and drainage valve 72, hydrogen off-gas is discharged from the FC stack 11 to the outside, but to compensate for this discharge, hydrogen gas (more specifically, a mixed gas of hydrogen gas and hydrogen off-gas) can be supplied to the FC stack 11. Therefore, when the exhaust and drainage valve 72 is open, a decrease in the power generation efficiency of the FC stack 11 can be suppressed.

[0064] <Second Example> Next, a second embodiment will be described, focusing on the differences from the first embodiment, and omitting a description of the commonalities with the first embodiment.

[0065] In this embodiment, as shown in Figure 5, if a predetermined time has elapsed since the FC stack 11 was started and there is no request to open the exhaust drain valve 72 (step S11: NO), the control unit 12 sets the measurement value of the upstream pressure sensor P1 multiplied by 0.528 as the first target downstream pressure of the ejector 64 (e.g., 5 kPaG), and sets a predetermined pressure (e.g., 60 to 80 kPaG) as the second target downstream pressure of the ejector 64 (step S12).

[0066] Then, as shown in FIG. 6, the control unit 12 repeatedly performs a process of performing a first control for a first predetermined time (e.g., 5 seconds) to control the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a first target downstream pressure (e.g., 5 kPaG), and a process of performing a second control for a second predetermined time (e.g., 1 second) to control the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a second target downstream pressure (e.g., 60 to 80 kPaG) (step S13).

[0067] In this manner, in this embodiment, the control unit 12 repeatedly performs a process of performing the first control for a first predetermined time and a process of performing the second control for a second predetermined time.

[0068] In this way, by performing a first control that controls the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a first target downstream pressure (e.g., 5 kPaG), it is possible to suppress a decrease in the circulation efficiency of the hydrogen off-gas even when the upstream pressure of the ejector 64 is low. Also, by performing a second control that controls the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a second target downstream pressure (e.g., 60 to 80 kPaG), it is possible to avoid a shortage of hydrogen gas supplied to the FC stack 11.

[0069] <Third Example> Next, a third embodiment will be described, but differences from the first and second embodiments will be described, and a description of commonalities with the first and second embodiments will be omitted.

[0070] 7 and 8, the control unit 12 performs a first control for controlling the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a first target downstream pressure, and a second control for controlling the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a second target downstream pressure, every predetermined time (for example, 5 seconds). Then, within this predetermined time (i.e., within the predetermined time required to switch between the first control and the second control), the control unit 12 performs a control such that the measurement value of the downstream pressure sensor P2 is continuously swept (i.e., continuously changed (up and down)) over time (step S23).

[0071] In this way, in this embodiment, the control unit 12 alternately performs the first control and the second control at predetermined time intervals, and controls the injection amount of the injector 63 so that the measurement value of the downstream pressure sensor P2 changes continuously over time within the predetermined time.

[0072] In this way, by performing the first control, it is possible to suppress a decrease in the circulation efficiency of hydrogen off-gas even when the upstream pressure of the ejector 64 is low, and by performing the second control, it is possible to avoid a shortage of hydrogen gas supplied to the FC stack 11.

[0073] Furthermore, when switching between the first control and the second control, fluctuations in the amount of hydrogen gas supplied to the FC stack 11 are suppressed, so the power generation efficiency of the FC stack 11 is stabilized.

[0074] It should be noted that the above-described embodiments are merely examples and do not limit the present disclosure in any way. It goes without saying that various improvements and modifications are possible within the scope of the gist of the present disclosure.

[0075] For example, in the third embodiment, the length of the predetermined time when switching from the first control to the second control may be different from the length of the predetermined time when switching from the second control to the first control. Furthermore, when the measurement value of the downstream pressure sensor P2 is continuously swept over time, it is not necessary to change the measurement value of the downstream pressure sensor P2 linearly (in a straight line) over time.

[0076] Furthermore, the fuel cell system 1 of this embodiment may be a so-called DCDC converter-less system in which no DCDC converter is arranged between the FC stack 11 and the battery (not shown). In this case, when the fuel cell system 1 is in an intermittent stop state (low current mode) in which power generation by the FC stack 11 is suppressed, the control unit 12 may perform a first control to control the injector 63 so that the measurement value of the downstream pressure sensor P2 becomes a first target downstream pressure calculated by multiplying the measurement value of the upstream pressure sensor P1 by a value equal to or less than the critical pressure ratio. [Explanation of symbols]

[0077] 1. Fuel cell system 11 FC stack 12 Control Unit 21 Hydrogen Systems 22 Air Systems 23 Cooling system 31 Hydrogen gas supply passage 32 Hydrogen off-gas exhaust passage 34 Hydrogen off-gas circulation passage 63 Injector 64 Ejector 72 Exhaust drain valve P1 Upstream pressure sensor P2 downstream pressure sensor PA atmospheric pressure sensor

Claims

1. A fuel cell; a fuel gas supply passage for supplying a fuel gas to the fuel cell; a fuel off-gas discharge passage for discharging fuel off-gas discharged from the fuel cell to the outside; a fuel off-gas circulation passage that circulates at least a portion of the fuel off-gas from the fuel off-gas discharge passage to the fuel gas supply passage; a fuel supply device disposed in the fuel gas supply passage and supplying the fuel gas; an ejector that is disposed downstream of the fuel supply device in the fuel gas supply passage and that mixes the fuel gas supplied by the fuel supply device and the fuel off-gas circulated through the fuel off-gas circulation passage and discharges the mixture; In a fuel cell system having a first pressure sensor that measures a pressure upstream of the ejector; a second pressure sensor measuring the pressure downstream of the ejector; a control unit that controls the fuel supply device, the control unit performs first control to control the fuel supply device so that the measurement value of the second pressure sensor becomes a first target pressure value calculated by multiplying the measurement value of the first pressure sensor by a value equal to or less than a critical pressure ratio; A fuel cell system characterized by:

2. 2. The fuel cell system of claim 1, an atmospheric pressure sensor for measuring atmospheric pressure; The first target pressure value is set to be equal to or higher than the atmospheric pressure measured by the atmospheric pressure sensor; A fuel cell system characterized by:

3. 3. The fuel cell system according to claim 1, The control unit performing second control of controlling the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value that is higher than the first target pressure value; repeating a process of performing the first control for a first predetermined time and a process of performing the second control for a second predetermined time; A fuel cell system characterized by:

4. 3. The fuel cell system according to claim 1, The control unit performing second control of controlling the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value that is higher than the first target pressure value; controlling the fuel supply device so that the first control and the second control are alternately performed at predetermined time intervals and the measurement value of the second pressure sensor changes continuously with the passage of time within the predetermined time; A fuel cell system characterized by:

5. 3. The fuel cell system according to claim 1, The control unit performing second control of controlling the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value higher than the first target pressure value until a predetermined time has elapsed since the start of the fuel cell; A fuel cell system characterized by:

6. 3. The fuel cell system according to claim 1, an exhaust drain valve that opens and closes the fuel off-gas discharge passage; The control unit performing second control of controlling the fuel supply device so that the measurement value of the second pressure sensor becomes a second target pressure value higher than the first target pressure value when there is a request to open the exhaust drain valve; A fuel cell system characterized by:

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